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Home , 2020 SW, Bruce Jakosky, Climate of Mars, Flag of Mars, Human mission to Mars, Mars Exploration Program

Mars, the Nearest Habitable World – A Comprehensive Program for Future Exploration

Report by the NASA Mars Architecture Strategy Working Group (MASWG)

November 2020

Front Cover: Artist Concepts Top (Artist concepts, left to right): Early Mars1; Molecules in Space2; and Rover on Mars1; Exo- System1. Bottom: Pillinger Point, Crater, as imaged by the rover1. Credits: 1NASA; 2Discovery Magazine

Citation: Mars Architecture Strategy Working Group (MASWG), Jakosky, B. M., et al. (2020). Mars, the Nearest Habitable World—A Comprehensive Program for Future Mars Exploration.

MASWG Members • Jakosky, University of Colorado (chair) • Richard Zurek, Office, JPL (co-chair) • Shane Byrne, • Wendy Calvin, University of Nevada, Reno • Shannon Curry, University of , Berkeley • , California Institute of • Jennifer Eigenbrode, NASA/ Flight Center • Tori Hoehler, NASA/ • Briony Horgan, • Hubbard, Stanford University • Tom McCollom, University of Colorado • John Mustard, • Nathaniel Putzig, Planetary Institute • Michelle Rucker, NASA/JSC • Michael Wolff, Space Science Institute • Robin Wordsworth, Harvard University

Ex Officio • Michael Meyer, NASA Headquarters

ii Mars, the Nearest Habitable World October 2020 MASWG Table of Contents

Mars, the Nearest Habitable World – A Comprehensive Program for Future Mars Exploration

Table of Contents EXECUTIVE SUMMARY ...... 1 I. INTRODUCTION ...... 5 II. MARS: A COMPELLING TARGET FOR SCIENCE AND EXPLORATION ...... 9 II.A Overarching Themes ...... 9 II.B Mars presents outstanding access to environments fundamental to the search for past and/or present signs of ...... 10 II.C Mars offers an unparalleled opportunity to study and habitability as an evolving, system- level phenomenon...... 12 II.D Mars is the best place in the system to study the first billion years of the evolution of a habitable ...... 14 II.E Outstanding opportunities for elucidating the climate and prebiotic and possible biological history of Mars informs our understanding of the evolution of ...... 17 II.F Mars is a compelling destination for human-exploration and science- exploration synergism...... 19 II.G International and Commercial Players ...... 21 III. FINDINGS ...... 22 IV. PROGRAMMATIC RATIONALE AND FUTURE OPPORTUNITIES ...... 32 IV.A Why a Mars Program is Necessary ...... 32 IV.B Small for Mars: A Programmatic Opportunity ...... 34 IV.C How to Involve Commercial and International Partners ...... 36 V. RECOMMENDATIONS ...... 41 V.A High-level Recommendations ...... 41 V.B MASWG Recommendations for a Successful Future ...... 43 VI. A MARS PROGRAM ARCHITECTURE FOR 2020–2035 ...... 48 VI.A Mission Classes for Mars Exploration...... 49 VI.B Program Architecture: Perspectives and Possibilities—Mission Arcs ...... 50 VI.C Program Scope and Affordability ...... 59 VII. IMPLEMENTING A MARS EXPLORATION PROGRAM ...... 62 APPENDICES ...... 64 Appendix A MASWG Meetings and Activities ...... 65 Appendix B Science Contamination Control and Considerations for the Future Mars Exploration Program ...... 66 Appendix C Small- Costs in the Context of Mars Exploration ...... 68 Appendix D References ...... 69 Appendix E List ...... 78 Appendix F Acknowledgments ...... 80

iii Mars, the Nearest Habitable World October 2020 MASWG

Hubble Space of Mars, obtained in 1999. The bright and dark areas on Mars are visible, along with the summertime north cap at the top of the image. are visible and prominent over the and looking to the planet's limb. (Credit: Science Institute and NASA)

iv Mars, the Nearest Habitable World October 2020 MASWG Executive Summary

Executive Summary

Mars exploration today is at a critical junc- detailed local measurements at representative ture. A series of successful orbital and landed sites across the planet. Also, fundamental spacecraft missions have revealed a planet questions about Mars will remain related to its with: potential for life; the geological history of the • A variety of environments that could be or planet; the history of its climate and the driving could have been habitable to microbes, forces behind these changes; the evolution of • An early, more -like climate that geologic processes and the interior composi- tion and structure; and more recent atmos- changed dramatically over time, pheric, polar, surface, and interior processes. • A geologically recent of ice ages, and Answering these questions will require new • A dynamic planet that still changes today. flight missions in addition to those needed for These missions have also provided a first MSR. look at the processes by which the planet has We have carried out a detailed analysis of evolved, addressing fundamental questions of the science and mission needs for exploring planetary evolution and providing a valuable Mars, and we have surveyed the emerging ca- end-member in the comparative study of terres- pabilities in order to provide a new vision of trial both inside our solar system and what the Mars Exploration Program should be beyond. The program of orbital reconnaissance during this era. Our activity was driven by a and ever more capable landed missions has recommendation from the mid-decadal evalua- taken the program to the point that it can under- tion carried out by the National Academies of take the challenge of returning—for the first , , and Medicine time—carefully chosen samples from the Mar- (NASEM) of NASA’s on implement- tian surface for intensive study by the full ca- ing the recommendations of Visions and Voy- pabilities of laboratories here on Earth. The ages. As part of its response, NASA chartered rover is on its way to this Mars Architecture Strategy Working Crater, where it will explore an ancient deltaic Group (MASWG) to assess the future of Mars environment and collect samples for possible exploration in addition to the current efforts to future return. NASA, in partnership with the complete MSR. (ESA), is developing In a rapidly changing environment of tech- follow-on missions for bringing those samples nical innovation, there are new opportunities to to Earth during the coming decade, as en- pursue the science, even while the challenges dorsed by the Visions and Voyages Planetary of retrieving samples from Mars are being met. Sciences Decadal Survey (National Research However, as in the past, it will take a focused Council [NRC], 2011). program that: As important as Mars Sample Return • Prioritizes the most important science, uti- (MSR) is—and it will result in a major step for- lizing new missions across a range of mis- ward for —examination of sion size classes and science objectives that material from a single site will not tell us eve- build on one another to meet the program rything that we need to know about Mars. objectives; Mars, like Earth, has a rich, complex history, with different locations capturing snapshots of • Leverages the development of new technical its path in space and time. The history of one capabilities (e.g., small spacecraft); and site must be integrated with a global context • Works with different NASA directorates provided by both global observations and and international and commercial partners

1 Mars, the Nearest Habitable World October 2020 MASWG Executive Summary in new—and possibly radically different— Spacecraft class ($100–300M in full life-cycle ways. cost) to Discovery- or New Frontiers-class (up Mars exploration is an immense challenge, to $1.25B). As proof of concept, we developed worthy of a program that has a history of meet- four series of missions (which we call “mission ing similar challenges. arcs”), each of which pursues a logical progres- We recommend a program that will inves- sion of missions in several different size classes tigate key areas of solar-system science, fo- by building scientifically and technically on cused on examining Mars as the closest poten- each successive mission and its anticipated re- tially habitable planet to the Earth. Mars pre- sults. Within these mission arcs, the progress sents: is often from initial investigation with smaller missions to detailed exploration of compelling • Outstanding access to environments funda- science objectives with more capable missions. mental to the search for past and/or present These arcs are examples of what the Mars Ex- signs of life; ploration Program could pursue, in consulta- • An unparalleled opportunity to study cli- tion with the Mars science community. mate and habitability as an evolving, sys- The significant role to be played by small tem-level phenomenon, with Mars and spacecraft derives from their high potential for Earth apparently having passed through carrying out significant Mars science, with the similar stages as they evolved to their pre- added excitement of being able to have a sent states; launch at nearly every opportunity every two • The best place in the solar system to study years. More capable missions (Discovery, the first billion years of the evolution of a New Frontiers, Flagships after MSR) will be habitable terrestrial planet; needed to address the most challenging objec- • Outstanding opportunities to inform our un- tives and discoveries. Implementation of the derstanding of the evolution of exoplanets missions in several of these science mission by investigating its climate and prebiotic arcs at the cadence proposed could be done for and possible biological history; and an estimated $300M/year through the first dec- • A compelling destination for human explo- ade and $500M/year beyond that (all in ration and science exploration synergism. FY20$); implementation of two of the arcs While every solar-system body has its own would cost about half this amount. Funding story to tell, Mars is unique in that it retains to- technology development and extended mis- a resilient physical record of change over sions would require an additional estimated most of its history—predominantly in the $150M/year. Pursuing four mission arcs ap- and atmosphere for the early history and in the pears to be affordable and would result in a ice and the present-day environment for more broad, truly compelling and exciting Mars Ex- recent times. Those records are accessible by ploration Program, while implementing fewer measurement, at first from and then arcs would still allow progress in addressing on the surface and in the atmosphere. Results fundamental questions about Mars. Clearly, from a continuing Mars Exploration Program the speed and depth of the science return will will be both invaluable and necessary for inter- depend on the number of arcs and, therefore, on preting data from MSR, for understanding the the funding invested in this program. formation and evolution of our solar system, In addition, we are on the verge of initiating and for understanding the history of planets serious planning for human missions to Mars, discovered outside of our solar system. with flights by NASA in the 2030s and perhaps Fundamental scientific exploration can be earlier by commercial entities. A reinvigorated carried out with missions ranging from Small Mars program must be initiated now in order to

2 Mars, the Nearest Habitable World October 2020 MASWG Executive Summary

support this planning and to be prepared for • MSR should proceed as currently planned, such missions. A robust Mars Exploration Pro- as it will produce a major step forward in our gram with new missions and payloads is neces- understanding of Mars, as envisioned by Vi- sary to provide sufficient knowledge about the sions and Voyages. environment to allow us to carry out • NASA should support missions that ad- human missions safely and would provide a dress fundamental science objectives at level of detail in our understanding of Mars to Mars in addition to MSR, using the full support planning the scientific exploration to range of technically viable mission classes. be carried out by human missions. During the MSR era, the emphasis should be The Mars Exploration Program that we are on achieving other high-priority science ob- recommending can best be implemented as a jectives, while developing the separate program within the Planetary Science needed going forward. Division. The justification for having a sepa- • To the extent possible, missions and instru- rate, dedicated program falls into three areas— ments should be openly competed; where scientific, programmatic, and exploration: specific investigations are desired, objec- • Scientific: Mars provides the opportunity to tives can be defined and then opened to explore the full range of processes and prop- competition. erties on terrestrial planets under different • For this next phase of Mars exploration, boundary conditions from Earth. Mars’ en- NASA should retain a programmatically tire history is preserved in an accessible rock distinct Mars Exploration Program. NASA record that includes the first billion years. should institute mission or budget lines that Mars also has key similarities with Earth can allow Mars-specific missions, from that allow us to understand the processes small spacecraft through New Frontiers- that operated, with enough differences to class missions, to be strategically integrated truly test our models and our understanding. into a program, with specific missions cho- • Programmatic: Mars is accessible enough sen and implemented as appropriate for the that multiple missions can be flown to ex- science to be achieved. plore the different components of the Mars • A robust Mars exploration program will re- environment, including substantial access to quire affordable access to multiple places on the surface. Past experience has shown that surface and affordable long- the Martian environmental system is com- lived orbiters. NASA should invest early to plex; understanding interactions between expedite the rapidly evolving small space- the different components, from the deep in- craft technologies and procedures to achieve terior to the upper atmosphere, requires mul- these capabilities at lower costs than past tiple missions that are well coordinated with missions and work with international and each other. commercial partners to achieve their deliv- • Exploration: Mars is NASA’s stated long- ery to Mars. term destination for human exploration. This Mars Exploration Program will ad- Precursor spacecraft missions are required dress fundamental questions of planetary sci- in advance of human missions so that we ence and build on the new capabilities to do so, can be ready for human missions to Mars. assuming a new steady funding line, at costs that are affordable while still maintaining a di- Within this reinvigorated Mars Exploration verse portfolio across the solar system. NASA Program, we make the following high-level can provide the leadership and programmatic recommendations: organization to work with the Mars community

3 Mars, the Nearest Habitable World October 2020 MASWG Executive Summary to choose and develop the right integrated se- These are the challenges that can be met by quences of missions that can address the com- the Mars Exploration Program to pursue com- pelling science; that can leverage the new tech- pelling science at Mars during an era of MSR nologies to make it happen; and that can con- and beyond. duct long-term planning to develop the needed partnerships both within the agency and with the ever-growing number of international space agencies, while developing new pathways for commercial partner involvement.

Burns Cliff, Crater, as imaged by the Opportunity rover. Some of the deposits on the walls show features indicative of having been deposited in standing bodies of water. (Credit: NASA/JPL)

4 Mars, the Nearest Habitable World October 2020 MASWG I. Introduction

Mars, the Nearest Habitable World – A Comprehensive Program for Future Mars Exploration I. Introduction

The allure of exploring Mars goes back history of the planet and how what happened more than a hundred years to the time of the there relates to other planets both in our solar astronomers Giovanni Schiaparelli and Perci- system and beyond have deepened. These val . They popularized both the scien- questions include (but are not limited to): tific exploration of the Mars surface and atmos- • Was there ever , and could any phere and the search for evidence of life. In still exist today at the surface or in the sub- that era, it was widely accepted that Mars could surface? have intelligent life, even to the point that Ni- • What was the ancient climate that once kola Tesla thought at one time in the early hosted surface rivers and lakes like, what 1900s that he was detecting signals from controlled it, and where did the CO2 and beings on Mars. With the advent of the explo- H O from the early environment go? ration of the solar system by spacecraft, became the second planet to be visited by • What geological processes have operated NASA spacecraft. Each spacecraft that has through time, and how have the interactions gone to Mars has carried a different set of ex- between the surface, interior, atmosphere, periments designed to measure different as- and external processes (including impacts pects of the planet, and each set of measure- and the ’s behavior) shaped the evolu- ments has made fundamental discoveries about tion of the planet? the red planet and contributed to our • What is the structure and composition of the knowledge that in many ways is second only to interior? the Earth in our detailed understanding. • How do the present-day climate and polar However, Mars exploration today is at a caps behave, what controls their behavior, critical juncture. A series of successful mis- and how have they responded on various sions into orbit and to its surface have revealed timescales to the changing tilt of the polar a planet that once hosted a variety of habitable axis? environments, an early more Earth-like climate • Why are the Mars surface, atmosphere, and that changed dramatically over time, a geolog- interior so different from those of Earth and ically recent epoch of ice ages, and a dynamic ? And what does this portend for the planet that still changes today. These missions study of exoplanets? have also provided a first look at the processes Finally, Mars is the only terrestrial planet by which that all happened, addressing funda- beyond the Earth- system that humans mental questions of planetary evolution and are likely to visit in the foreseeable future. That providing a valuable contrast in the compara- raises two additional questions: tive study of terrestrial planets. • What knowledge is needed in advance for Today, the high scientific and exploration humans to be able to explore Mars? value of Mars exploration have made it a major • How can human explorers in orbit or on the thrust of the robotic exploration of our solar best address fundamental system. As we have learned more and discov- science questions? ered the rich historical archive preserved at Mars, our fundamental questions about the

5 Mars, the Nearest Habitable World October 2020 MASWG I. Introduction These questions about Mars are fundamen- scientific issues can be resolved by the analysis tal to understanding the history of the planet of returned samples. Questions about the na- and the implications of either a discovery of life ture of the present-day climate and its evolution or a demonstration that life was not present. and about global-scale processes and properties That so many basic questions exist even after need to be addressed in order to have a broad all of the spacecraft missions to the planet picture of the context and implications of the should not be surprising. As we know from our sample analysis—understanding the global pic- own planet, after the initial surveys, the ques- ture of Mars’ behavior is necessary in order to tions become more detailed as to how and why, put the sample-analysis results into the broader as well as what. Mars, like Earth, is a complex context of Mars as a planet. Additionally, as on planet, and at an elementary level, we really do Earth, a single location does not record all im- not yet understand how planets work or why portant evolutionary junctures of a planet’s ge- Mars and the other terrestrial planets (including ologic history. Earth) evolved as they did. This next 10–15 years is a period in which The program of orbital reconnaissance and MSR is being implemented. It also is a period of deployment of ever-more capable missions when the human exploration programs will to its surface has brought the program to where begin looking beyond current activities in order it can undertake the challenges of returning— to establish human presence on Mars. It is a for the first time—carefully chosen samples time when the very of exploration in from the surface back to Earth for intensive deep space is rapidly changing, as new interna- study by the full capabilities of laboratories tional partners and commercial entities bring here. Perseverance is on its way to its Jezero new approaches, perspectives, and capabilities Crater landing site, where it will explore an an- to the endeavor. What should the future of the cient deltaic environment and collect and pre- Mars Exploration Program be during this era? pare samples for future return. In partnership Our objective here is to examine the broad with ESA, NASA is developing missions to set of scientific questions about Mars and its re- bring those samples back to Earth, as endorsed lationship to the solar system and to exoplane- by the previous Planetary Sciences Decadal tary systems, and to put forward the rationale Survey (NRC, 2011). That effort is itself a dec- for carrying out a Mars Exploration Program in ade-long activity, involving development and addition to MSR. We examine the scientific flight of multiple spacecraft elements. questions that need to be addressed, the range The scientific goals for Mars are to under- of mission concepts that can address them, and stand its evolution and its environment and to how they might fit into a program of robotic look for evidence of past life that might be re- . tained in the rock record. The scientific results This MASWG arose out of the mid-decadal from past missions, from analysis of evaluation by the NASEM of the 2012 Decadal from Mars, and from Earth-based telescopic Strategy for Planetary Sciences (NRC, 2011). observations point unequivocally to sample re- The charter for the mid-decadal evaluation turn as being the next important step that will (NASEM, 2018) included a request from allow us to address many of the major scientific NASA to evaluate the status and progress of the questions about Mars. Mars Exploration Program. That evaluation in- As important as MSR is—and it will result cluded the following recommendation: in a major step forward for planetary science— examination of a single site on a diverse plane- “Recommendation: NASA should develop a tary landscape with a complex history will not comprehensive Mars Exploration Program tell us all that we need to know. Also, not all (MEP) architecture, strategic plan,

6 Mars, the Nearest Habitable World October 2020 MASWG I. Introduction management structure, partnerships (including goals outlined in Vision & Voyages and up- commercial partnerships), and budget that ad- dated in the MEPAG Goals Document. dress the science goals for Mars exploration • Define a mission candidate portfolio to outlined in Vision and Voyages. The architec- guide future MEP planning including, but ture and strategic plan should maximize syn- not necessarily restricted to, missions in the ergy among existing and future domestic and competed small spacecraft, Discovery and international missions, ensure a healthy and New Frontiers categories [classes], which comprehensive technology pipeline at the ar- may also be considered by the upcoming chitectural (versus individual mission) level, Planetary Decadal Survey (2023–2032). and ensure sustenance of foundational infra- • Define strategic mission candidates, tech- structure (telecommunications, imaging for nologies, infrastructure, and partnerships site certification, etc.). This approach of man- (international and commercial) able to ad- aging the MEP as a program, rather than just dress compelling science in the specified as a series of missions, enables science optimi- time horizon, showing their programmatic zation at the architectural level. This activity linkage.” should include assurance that appropriate NASA/MEP management structure and inter- The objective of MASWG is to build on the national partnerships are in place to enable science priorities and mission concepts in the Mars sample return.” (p.6) Mars Exploration Program Analysis Group (MEPAG) goals and objectives document In response, NASA chartered MASWG to (MEPAG, 2020) and in the decadal strategy make specific recommendations on the devel- (NRC, 2011). It was not intended to either up- opment of a science program and mission ar- date or replace those science priorities. In par- chitecture that would address high-priority sci- allel with our committee work, the MEPAG ence objectives in addition to those that would goals and objectives were being updated, and be addressed by the MSR mission campaign; MASWG benefited from briefings on the na- these are the initial steps in developing the full ture of those updates. Our report was com- response to the questions from the mid-decadal pleted in time to be provided as input into the review. The key components of the MASWG new decadal strategy analysis now in progress. charter are: In a rapidly changing environment of tech- “In response, NASA is forming a group of nical innovation, there are new opportunities to 12–15 scientists [plus engineers and manag- pursue that science, even while the challenges ers] to develop such a Mars exploration strate- of retrieving samples from Mars are being met. gic plan. The same Midterm Review endorsed However, as in the past, it will take a focused MEP’s current efforts to ‘continue planning program that 1) prioritizes the most important and begin implementation of its proposed... ar- science, utilizing a range of missions (“mission chitecture to return samples from the Mars arcs”) that build on one another to meet the pro- 2020 mission...’ Given that priority, the tasks gram objectives; 2) leverages the development to be addressed by this panel are: of new technical capabilities (e.g., small space- craft); and 3) works with different NASA di- • Determine what could and should be done rectorates and international and commercial beyond (i.e., in addition to or after) the Mars partners in new—and possibly radically differ- Sample Return campaign. ent—ways. It is an immense challenge, worthy • Survey the compelling science addressable of a program that has met challenges of a simi- by various classes of missions during the pe- lar scope previously. MASWG believes that it riod 2020–2035, building on the science can be done.

7 Mars, the Nearest Habitable World October 2020 MASWG I. Introduction In what follows, the case that compelling sion architecture are then presented to show science can and should be achieved at Mars in how programmatic progress on high-priority addition to MSR is developed, and key science science can be made during and after the pre- questions are highlighted. While every solar sent era of MSR. system body likely has its story to tell, Mars is Membership within MASWG was intended unique in that it provides a resilient physical to be broad across science disciplines, degree record of that change over time—in the rock for of seniority/experience within their careers, the ancient climate and in the ice for more re- and demographic diversity. While broad rep- cent geologic times. Those records are acces- resentation of the science disciplines was seen sible by measurements, at first from orbit and as necessary, there was no attempt to include then in situ on the surface. Possibilities for ob- “one from every discipline,” as we strove to taining the necessary data are discussed in the demonstrate proofs of concept for program- context of a program, enabled by new develop- matic mission architectures and not to act as a ments in spacecraft capabilities, including the science definition team for any specific queue maturing technology of small spacecraft. of missions. Meetings and activities of Some example proof-of-concept “arcs” of mis- MASWG are described in Appendix A.

This artist's concept illustrates the promise that the relatively pristine and accessible rock records of Mars—unique in the solar system—may tell the story of a planet's evolution from origin of life to its possible existence today.

8 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target

II. Mars: A Compelling Target for Solar System Science and Exploration

II.A Overarching Themes However, habitability is a time-dependent con- dition, dependent on climate and shaped by life Mars has a uniquely accessible archive of itself, if it occurs. When we talk about Martian the long-term evolution of a habitable planet. habitability, we mean the conditions that affect This record spans almost the entire range of habitability, how they’ve changed through ages of surfaces on the terrestrial planets in our time, and the processes that have controlled solar system, with materials that may retain a them. Did the window for life’s emergence record of the full range of processes that can close too quickly on Mars, or did it not close at occur. This provides a remarkable opportunity all, with life even today in refugia not yet ex- to study the interplay between processes and plored? the means by which the primary characteristics To deal with this complexity, we’ve di- of a planet have controlled them. The well-ex- vided the full range of science at Mars into five posed and well-preserved 4-billion-year-plus themes for discussion, recognizing that the record of physical and chemical planetary pro- crossover or interplay between areas is just as cesses is unique in the solar system because of important as the discrete areas themselves. its high degree of preservation, accessibility, These five themes are as follows: and importance to understanding . This record includes planetary • Mars presents outstanding access to envi- formation, impact bombardment, interior and ronments fundamental to the search for past crustal processes, atmospheric and climate evo- and/or present signs of life. lution, and potentially the origin and evolution • Mars offers an unparalleled opportunity to of life on another planet. The high degree of study climate and habitability as an evolv- preservation of materials at all ages allows ing, system-level phenomenon. these processes and their interaction to be • The best place in our solar system to study tracked throughout time, and should provide a the first billion years of evolution of a ter- record that can be interrogated to understand restrial, habitable planet is Mars. the evolution of habitability by microbes and • Outstanding opportunities for elucidating get a definitive answer as to whether life ever the climate and prebiotic and possible bio- existed on Mars. logical history of Mars informs our under- Habitability of a planetary environment de- standing of the evolution of exoplanets. pends on many factors. These include geologic • Mars is a compelling destination for human- supply of water and the building blocks of life, exploration and science-exploration syner- atmospheric control of climate and surface liq- gism. uid water, and the Sun’s influence on atmos- These are summarized in Figure II-1, and pheric evolution. We know that Mars, early in each is discussed in turn below. The Martian its history, had the necessary elements for life environmental system is a complex, intercon- and had liquid water on its surface and in the nected system, such that progress in one area near subsurface (Grotzinger et al., 2015). It ultimately requires progress in multiple areas. also appears that today, much of the surface is The processes occurring on modern Mars have hostile to life as we know it, and so the Mars operated in the past, while responding to differ- Exploration Program has sought to exploit the ent conditions (e.g., atmospheric composition preserved physical record to find evidence of and ) and forcing functions (e.g., life that may have arisen early on the planet.

9 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target

Figure II-1. Summary of the overarching themes for the scientific exploration of Mars as put forward in this report.

insolation at the or a faint young Sun). Mars preserves a record of early and di- For example, the water cycle—the phase, dis- verse environmental conditions that is not pre- tribution, and recycling of water—is important sent on Earth due to surface and crustal pro- to life and alters the surface and climate. It is cesses that have erased much of the first billion intimately connected to other cycles of CO2 years of our planet’s history. As a result, we and of dust. Measurements addressing ques- largely lack observational constraints on tions in one area benefit from measurements the environments, conditions, and processes designed to answer questions in another area. that prevailed during the critical time of life’s More often than not, the answer to a fundamen- emergence on Earth. The relatively intact rec- tal question (such as whether life was present) ord of environmental conditions during this pe- requires integrating different types of measure- riod on Mars is thus a unique resource for un- ments (biological, geological, meteorological) derstanding the emergence of life in the inner to arrive at an accurate understanding. solar system.

II.B Mars presents outstanding Mars was habitable—was it ever inhabited? access to environments fundamental to the search for From what we know today, Earth and Mars past and/or present signs of life. likely passed through similar phases of early habitability. If life is or was ever present on The question, “Are we alone?” is by no Mars, the early Mars rock record offers the po- means exclusive to science. Central to our tential to advance our understanding of life’s sense of place in the universe, it is as much hu- origins in the specific context of the environ- manistic as scientific; however, it is in the rig- ments from which it emerged. Similarly, the orous methodology of planetary science and as- absence of life on Mars would yield an equally tronomy that an answer can be pursued, and we valuable opportunity to explore a record of are now capable of doing so. Similarly, this early chemical evolution that failed to give rise fundamental question is by no means exclusive to and to understand that failure within to Mars or even solar-system science, but mul- the environmental context. Either alternative tiple factors make Mars a premier venue in will serve to greatly improve our understanding which to investigate it.

10 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target of our own origin—how, and how commonly, contribute to prebiotic chemical evolution and life emerges in an Earth-like setting. More gen- support the transition from abiotic to biologi- erally, as a rocky planet within its traditional cal. Absent such knowledge, environmental di- stellar habitable zone, Mars serves as an im- versity and broad similarity to a setting in portant and accessible second example of the which we know life can emerge become key type of that will be targeted in a tel- considerations in targeting a search for evi- escopic search for life. dence of life beyond Earth. Importantly, the The search for evidence of life on Mars is extensive body of work that has sought to doc- both motivated and supported by spacecraft ob- ument evidence of life in ancient Earthly envi- servations that have provided extensive envi- ronments that are similar to those on Mars in- ronmental characterization and that inform our forms both the methodology with which to con- understanding of where and how to most pro- duct such a search on Mars and the ability to ductively conduct that search. Extensive ob- interpret what we observe. servation of diverse surface environments, at The Visions and Voyages Decadal Survey scales from microscopic to global, has revealed assigned high priority to the identification of the presence of conditions that could have sup- ancient and modern habitable environments ported life during Mars’ early history and also and the investigation of whether life emerged preserved evidence of life over geologic time or now exists in those environments (NRC, scales (Arvidson et al., 2008; Eigenbrode et al., 2011). The systematic characterization of 2018; Grotzinger et al., 2015; Hassler et al., Mars has revealed both ancient and potentially 2014; Murchie et al., 2009; Stoker et al., 2010). modern habitable environments, and we are Recent work has now identified a variety of now indeed poised to pursue a well-informed possible “refugia”—caves, deep subsurface, search for evidence of life there. subsurface ice, salt deposits, or some combina- A sequence of missions has now com- tion of conditions thereof—that could preserve menced that represents the beginning, and not modern records of life (alive within the most the end, of a quest to understand whether and recent 10 Ma or now dormant) and that could how life took hold on Mars and persists into the potentially host extant life (Carrier et al., 2020). present. NASA’s Perseverance The ability to access these largely unexplored rover mission is the next step in the search for domains in situ is rapidly evolving (e.g., evidence of ancient life, with the capability to for extreme terrain, deep electromagnetic [EM] detect macroscopic features associated with sounding from landers, and extended drilling) microbial communities, such as , and the debate is about where is (are) the best in exhumed sediments. Return to Earth of sam- place(s) to look (Hays et al., 2017; Onstott et ples cached by Perseverance as part of an in- al., 2019). ternational MSR program will enable the most detailed and comprehensive analysis yet of or- Can Mars ever tell us about the conditions ganic composition and textural features in care- sufficient for the origin of life? fully chosen surface samples. Prior to that, ESA’s 2022 ExoMars rover mission will search The diversity of environments that are and for organic molecular signatures of life in very were present on Mars, and their likely similar- early () -rich sediments by drill- ity to those on early Earth, is an important fac- ing to a depth of 2 m at which the damaging tor in the search for life. We lack a detailed effects of ionizing should be mini- understanding about the bearing of environ- mized. mental conditions on life’s emergence, and of These missions have the potential to be pro- the specific processes and settings that foundly enabling to a new chapter of in situ

11 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target Mars exploration whether or not they reveal ev- Mars’ rock and volatile record allow us to study idence of life. Uncovering substantive evi- interactions among interior, atmospheric, and dence of life on Mars would motivate subse- impact drivers of climate and habitability, and quent efforts to understand its emergence in the their evolution over time. The present climate context of the host environment and its similar- is observable directly, whereas the record of ities and dissimilarities relative to life on Earth, past climate is stored in the volatile deposits of and to determine whether it has persisted to the the polar caps, the crustal rock record, and evo- present in accessible refugia. The latter objec- lutionary signatures present in today’s atmos- tive, to seek evidence of recent or extant life, phere. This ancient record has been largely lost will almost certainly require in situ investiga- or altered on Earth, so the Martian surface pro- tion. Uncovering “hints” of life would surely vides a unique view into the early history of the motivate further sampling to seek definitive ev- solar system. idence, and finding no evidence of life would raise a series of sequel questions to be ad- The Ancient Climate: Whether or warm, dressed in situ: Does the Martian record pre- how did early Mars get so wet? Solving this serve evidence of abiotic or stalled prebiotic mystery is key to understanding planetary chemical evolution? Have environmental fac- and their evolution. tors created a potential for false negative re- sults? Could another of Mars’ diverse environ- Mars’ earliest period of evolution is partic- ments, rather than the one sampled, contain ev- ularly enigmatic. There is robust evidence for idence of life? Or is there something in the habitable surface conditions in Mars’ early his- Mars environment that precluded an origin of tory, yet its orbit and the lower luminosity of life? the young Sun suggest that the surface should Ours could be the generation that discovers have been permanently frozen. This “faint evidence of life beyond Earth. Advancement young Sun” problem for Mars is one of the ma- in planetary science and exploration technol- jor outstanding questions in planetary science, ogy have left us poised to do so as never before. with implications for Earth, Venus, and extra- The accessibility of known diverse habitable solar planets. Significant progress has been environments on Mars makes it a premier made towards solving this problem over the venue in which to seek such evidence, and ex- last few decades, and it is now thought that the isting technology or that which can plausibly solution most likely lies in some combination be developed in the next decade allows us to do of an enhanced greenhouse effect from a so. thicker early atmosphere along with local and/or transient factors. Nonetheless, major II.C Mars offers an unparalleled questions remain about the size and composi- opportunity to study climate and tion of the early Martian atmosphere, the sur- habitability as an evolving, face conditions, and the early volatile inven- system-level phenomenon. tory, including whether or not Mars ever pos- sessed an extensive northern The Martian climate has evolved dramati- (Wordsworth, 2016) and what the role was of cally through time, from an early phase with the loss of Mars’ atmosphere to space (Jakosky abundant liquid water to today’s cold and dry et al., 2018). For many planets in our solar sys- surface. As discussed previously, Mars shows tem, including Earth, only scraps of evidence us that habitability is a time-dependent phe- remain about conditions 3–4 billion years ago, nomenon governed by interacting processes but Mars’ excellent surface preservation from that occur over a range of spatial and temporal this time period means that there is still a scales. The longevity and accessibility of

12 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target treasure trove of information from this habita- lack of large standing bodies of water and the ble time period waiting to be fully accessed and associated complexity in the hydrological cy- studied. cle. Nonetheless, the CO2 volatile cycle, dust Middle Mars: Understanding the factors cycle, and water cycle all play significant cli- controlling ice ages on recent Mars. matic roles, and many aspects of their behavior on both short and longer timescales remain Mars’ climate evolution since this early pe- poorly understood (Haberle et al., 2017). Char- riod is also unique in the solar system and has acterization of the dust cycle is an example of great potential to teach us about environmental another area that is important both from a fun- processes that are analogous to, but still very damental science perspective and for effective different from, those on Earth. Because of its mission planning. Understanding all these pro- orbit and lack of the stabilizing influence of a cesses on Mars adds to our knowledge of cli- large moon, Mars’ (its axial obliquity) mate science as a general discipline by exten- evolves chaotically on timescales of millions of sion outside a purely Earth-like regime. years and greater. Consequently, seasonal inso- The distribution of habitable environments lation patterns vary widely over geologic time, on Mars has changed over time along with the which has led to repeated migration of both evolving climate. Exploration of Mars over the CO2 and water ice deposits across the planet’s last several decades has established that the key surface. As a result, volatile deposits both at the ingredients for life as we know it (liquid water, poles and at lower record a history of a suite of life-essential elements, and a source Mars’ changing climate. Characterization of of metabolic energy) were likely present at nu- the extent and nature of these deposits across merous, diverse locations across early Mars the surface is a major scientific goal (Diniega (see Figure II-2) (Hays et al., 2017; Onstott et & , 2020) that has significant implica- al., 2019). These widespread environments tions for in situ resource utilization (ISRU) by may retain evidence of conditions in the early future human missions, and possibly for astro- solar system at the time when life emerged on biological objectives. Understanding the evolu- Earth and may even harbor vestiges of Martian tion of volcanism, glacial processes, and sub- life forms. Over time, the onset of cold, dry surface hydrology from the Noachian (~4 bil- conditions has placed severe limitations on lion years ago) to the present day is also of fun- possible habitable environments on the planet’s damental importance from a comparative plan- surface, but conditions suitable for life may etology perspective. have persisted to modern times in the subsur- face (Stamenković et al., 2019). Modern Mars: Current processes are key to A deeper understanding of the biological the past. potential of Mars requires more detailed char- acterization of the habitable environments and Mars’ present-day climate also continues to how they changed over time, as well as deter- hold many mysteries and poses both challenges mination of the underlying causes that brought and opportunities for surface exploration. Pre- about these changes. The findings can lead to sent-day Martian meteorology is in some ways new insights about the distribution of life, both simpler than that of Earth, in part because of the within our solar system and beyond.

13 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target

Figure II-2. Example of a habitable, and possibly once inhabited, environment on early Mars. The left image shows digitate silica deposits formed by a hot spring in crater, Mars, that was explored by the rover. The image on the right shows similar structures formed in a terrestrial hot spring in Chile. The terrestrial deposits contain abundant indicating that biological organisms were present when they were formed and may have played a fundamental role in their formation. The similarities between the deposits raise the intriguing possibility that may have been involved in the formation of the Martian deposits as observed for the terrestrial example. Image modified from Ruff and Farmer (2016). Cratering chronology and superposition rela- II.D Mars is the best place in the solar tionships show that >50% of the Martian sur- system to study the first billion face is >3.5 Gyr old (Tanaka et al., 2014), en- years of the evolution of a compassing pre-Noachian, Noachian, and habitable terrestrial planet. Early eras. Sediments in Crater suggest an age of 4.21±0.35 Gyr for the sur- Many fundamental questions about the rounding watershed (Farley et al., 2014), crys- origin and early persist due to talline igneous lithologies in Martian - the paucity of unaltered ancient materials. In ites are dated as old as 4.1 Gyr (or older), and contrast, Mars presents outstanding access to the oldest age in the breccia NWA well-preserved ancient terrains that record the 7034 is 4.4 Gyr (Cartwright et al., 2014). These end of planetary formation, the early geophys- data show that Noachian-aged rocks encom- ical and geological history, the early evolution pass this critical early period of planetary evo- of an atmosphere, and chemical evolution pos- lution of a habitable planet, erased from Earth sibly leading to an origin or existence of life. and not accessible on Venus. The crust of Mars is likely the only such rela- tively unaltered physical record in our entire Studying Mars will revolutionize our solar system, as rocks of a similar age are not understanding of the coupled early geological, known to be accessible on Venus, and ancient geophysical, and atmospheric evolution of terrains on the Moon and do not pro- Earth-like worlds. vide the same into atmospheric evolu- tion, water, and habitability. Geomorphology, geochemistry, and miner- Mars contains the best-preserved rock rec- alogy from Noachian terrains show that the an- ord from the early period of planet evolution. cient well-preserved record is diverse.

14 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target Unaltered crystalline igneous rocks that record Mars provides a fundamental test for our magmatic events in the , crust, and sur- models of accretion, differentiation, core for- face are widely distributed in fault scarps, im- mation, magnetic-field generation, and volatile pacts (walls, ejecta, and central peaks) and vol- evolution. However, the basic 3D architecture canic flows (e.g., Mustard et al. [2005]). Impact of the planet, including internal layering, thick- and volcanically induced hydrothermal sys- ness of the crust, nature of the core and compo- tems as well as groundwater aquifers are wide- sition of the mantle, and tectonic history, is still spread. While well-known sedimentary depos- poorly understood (e.g., Plesa et al. [2018]), its in locations like Mawrth Valles (Poulet et even with the new constraints from InSight al., 2020) and Jezero Crater (Goudge et al., (e.g., Banerdt et al. [2020]). These parameters 2015) are testimony to active sedimentary sys- define the key dimensions for the origin and tems from the Noachian era, there are numer- fate of terrestrial planets, as the structure and ous other systems in Noachian terrains. Multi- dynamics of the interior are fundamental con- ple observations suggest that sedimentary pro- trols on the evolution of Mars, surface condi- cesses were active in the early Noachian, in- tions, and the release of water and atmospheric cluding evidence for extensive erosion and gases. Mars also retains a record of early solar deposition starting by the early Noachian system bombardment that is distinct from that (Irwin et al., 2013) and intriguing gigantic lay- on the Moon (e.g., Moser et al. [2019]) that, if ered breccia blocks in Isidis Basin ejecta quantitative dates for major impact events and (Mustard et al., 2009). a better estimate of impactor flux at Mars can This extensive sedimentary and aqueous be obtained, would provide critical independ- record also likely preserves key chem- ent constraints on early solar system history. ical records of the origin and evolution of the A major outstanding question for the first Martian atmosphere. The nature, duration, and billion years of Mars that illustrates the inter- composition of primary and secondary atmos- connectivity of key knowledge gaps is, “How pheres on terrestrial planets are poorly con- and when did phyllosilicate-bearing Noachian strained, and the record on Mars may provide crust become so extensively altered?” Scarps; important constraints on what Earth’s and other impact central peaks, walls, and ejecta; and ex- planets’ atmospheres looked like prior to the humed landscapes in Noachian crust are perva- influence of processes like and sively altered, but Hesperian rocks are much photosynthesis (Lammer et al., 2018). In addi- less likely to be altered (Bibring et al., 2006). tion, Mars provides valuable insights into Hypotheses include low-grade metamorphism, which properties of the atmosphere or planet diagenesis, or hydrothermal alteration enable an early warm climate and habitability. (Ehlmann et al., 2011); surface/near-surface The faint young Sun paradox presents chal- weathering (Carter et al., 2015); alteration by lenges for models of both early Earth and Mars impact-generated hydrothermal systems (Wordsworth, 2016), but reconciling these (Osinski et al., 2013); and alteration by an early models with geologic indicators for at least supercritical steam atmosphere ( et al., some periods of warm climates has led to novel 2017). These observations are important for hypotheses for warming mechanisms (e.g., understanding models of water and climate his- Halevy and Head III [2014]; Ramirez et al. tory, so when and how this alteration occurred [2014]; Haberle et al. [2019]). is fundamental for determining the first billion years of Mars’ evolution.

15 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target

Thousands of locations with water-formed on Mars, identified with CRISM, OMEGA, and THEMIS, record the history of water-rock reaction over the first billion years and beyond (Ehlmann & Edwards, 2014). The Martian geologic record will provide distribution), and we do not have robust con- critical insight into which factors in planetary straints for the conditions under which they evolution lead to sustained habitable formed (climate, water properties, and diagen- environments and possibly the origin of life. esis). Because of these knowledge gaps about Mars is currently the only planet where the Mars and the lack of a detailed record from the surface is known to have made the transition early Earth, we do not yet have a model for from habitable (by microorganisms) to appar- which factors in planetary evolution control the ently uninhabitable, but the driving mecha- habitability of terrestrial planets in the solar nisms for environmental change on Mars are system and beyond. Studying early environ- still poorly understood. Evidence has accumu- ments on Mars will enable us to move past the lated for a wide variety of ancient habitable simple concept of the habitable zone to a more aqueous environments on Mars, including per- robust understanding of the habitability of sistent lakes, extensive fluvial networks, wide- Earth-like planets over time (Ehlmann et al., spread surface weathering, and hydrothermal 2016). In addition, the depth and breadth of the systems (e.g., Grotzinger et al. [2015]; Ruff et Martian geologic record means that it is possi- al. [2020]; Arvidson et al. [2014]). We also ble that Mars preserves evidence of prebiotic now know that subsurface fluids were common synthesis and the origin of life. on Mars (e.g., aquifers, diagenetic fluids, and fracture-hosted deep groundwaters) (Ehlmann We haven’t yet visited the oldest terrains on et al., 2011) and that these subsurface environ- Mars in situ, and many critical data sets have ments may have provided a stable refuge for not yet been collected. life (Michalski et al., 2013). However, we still do not understand how these surface and sub- The Mars 2020 Perseverance rover will surface environments evolved over Mars his- visit ancient fluviolacustrine sediments in tory (their timing, persistence, and Jezero Crater that may date from the first

16 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target billion years of Mars history (e.g., Goudge et number of planets, more detailed information al. [2015]) and may get the opportunity to visit has been obtained, including atmospheric com- ancient crustal exposures and impact basin de- position and structure. In some posits. ExoMars will also visit one example of cases, the presence of atmospheric clouds and ancient altered Noachian crust (Vago et al., hazes has also been inferred (Madhusudhan et 2017). However, these missions are just begin- al., 2016). ning to scratch the surface of the deep record The best characterized exoplanets so far are preserved on Mars. In addition, several key in the hot- to sub- class. All of global datasets are insufficient to address im- these are planets about 10 times more massive portant questions. In particular, the geophysical than Earth or more and possess -rich properties of the Martian crust (, mag- atmospheres. Recently, atmospheric observa- netic field, etc.) are much less well-constrained tions have begun to push down toward the than bodies like the Moon and can provide im- rocky planet regime (e.g., Diamond-Lowe et al. portant insights into the early evolution of [2018]; Kreidberg et al. [2019]), and the next Mars. decade will see a significant expansion of ob- servations in this size class. Close-in, hotter II.E Outstanding opportunities for rocky planets around red dwarf stars (M stars) elucidating the climate and will initially be the most observable cases prebiotic and possible biological (Morley et al., 2017), and surface properties history of Mars informs our (temperature, , presence of liquid wa- understanding of the evolution of ter) are likely to remain hard to retrieve, at least exoplanets. in the intermediate future (Loftus et al., 2019; Robinson et al., 2010). The rapid growth in the study of exoplanets over the last two decades has affected many as- Although exact Mars-analogue exoplanets pects of solar system planetary science, and remain out of reach for now, the broader Mars research is no exception. Over 4,000 ex- intellectual links between Mars and exoplanet oplanets have now been discovered. For most science are profound. exoplanets, the only information we have is the host star type and the planet’s orbital distance, One particularly relevant is atmos- radius, and/or mass. However, observational pheric loss to space. Modeling suggests that the techniques are improving continually, and for a high rates of and XUV

Mars and Earth alongside artist’s impressions of three exoplanets recently discovered in the same system by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission. Processes operating at Mars that affect its climate history also may be acting on exoplanets. (Credit: NASA)

17 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target irradiation around M stars may be effective at that is available for detailed study in our solar stripping rocky-planet atmospheres in these system. Specific process-driven questions re- systems, but many aspects of the fundamental garding, for example, the efficiency of bound- dynamics, radiative transfer, and chemistry of ary layer heat transport at low atmospheric loss processes remain highly un- (Wordsworth, 2015) can be studied in situ at certain. Detailed observations of the Martian Mars to constrain models of planets orbiting upper atmosphere provide a vital testbed for many light-years away from our own Sun. general models of loss processes that are also applied to exoplanets (Jakosky et al., 2018). Mars: A solar system analogue for exoplanet Because of the predicted efficiency of at- evolution. mospheric loss for rocky exoplanets around M stars, it is also hypothesized that many such A final example is the long-standing debate planets may have small surface water invento- on the relative roles of orbital distance from the ries compared to Earth (e.g., Tian and Ida host star and planetary mass in determining [2015]). Here, again, Mars is an important solar habitability. Mars has evolved from being a system analogue, given that it has a small H2O planet with habitable surface conditions in the inventory, but (unlike, say, Venus) it still un- distant past to a mainly inhospitable state to- dergoes a water sublimation-condensation cy- day. This transition has been driven by a com- cle with surface ice migration, has radiatively bination of factors, and there is debate about the active water clouds, and exhibits coupling with extent to which Mars’ distant orbit (which the dust and CO2 cycles. Many of the unique makes warm surface conditions hard to aspects of the modern Martian water cycle achieve) versus its small size (which likely compared to Earth are likely to be of relevance caused early shutdown of plate tectonics, if it to understanding arid exoplanets. occurred at all, and enhanced loss of the atmos- Mars also provides an important window phere to space) was more important (Ehlmann into the links between atmospheric escape and et al., 2016). In the future, intercomparison of planetary chemical evolution. The redox state Mars with a range of exoplanets will allow us of the Martian surface seems to have evolved to bind solar system insights to new observa- significantly through time (Hurowitz et al., tions and build a general understanding of 2017; Lanza et al., 2016; Wadhwa, 2001), rocky planets on the edge of habitability. likely in large part due to the changing balance Further example analogues beyond those between hydrogen loss to space and supply of given here are likely to emerge in the coming volatiles to the atmosphere through , years as exoplanet science develops. Compre- impactor delivery, and other processes. This hensive study of fundamental processes on evolution has major implications for the possi- Mars can provide a strong foundation for un- ble development of life and for definitions of derstanding the complex pathways of evolution atmospheric biosignatures on exoplanets. for planets where detailed observations will not Also, highly relevant to exoplanets is “at- be possible for a very long time. In all cases, mospheric collapse,” the phenomenon whereby Mars can serve as the natural laboratory or the atmosphere of an exoplanet condenses out proxy for these numerous worlds, thereby ena- on the surface due to extreme pole-equator or bling our understanding of the fundamental day-night temperature differences (Joshi et al., physical, chemical, geophysical, geological, 1997). Having CO2-ice poles in dynamic equi- and potentially biological processes that may librium with its CO2-dominated atmosphere, occur there. Mars is a prime example of this phenomenon

18 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target II.F Mars is a compelling destination human Mars program by assisting in risk miti- for human-exploration and gation for crewed systems. For example, dust- science-exploration synergism. storm data collected by the Opportunity rover has been instrumental in sizing human-scale After the Moon, Mars is the next most ac- surface power system concepts (Rucker et al., cessible and, from a human perspective, the 2016), which in turn will allow tighter contin- most hospitable destination in our solar system. gency margins, reducing mass and cost. The Although Mars has long been a “horizon” goal Mars In-Situ Resource Utilization Ex- for NASA and, to date, human Mars explora- periment (MOXIE) on the Perseverance rover tion has been limited to a series of architecture will manufacture oxygen from dioxide, studies, current national policy explicitly calls demonstrating in situ utilization of Martian re- for eventual human missions to Mars (Review sources. Science can also contribute to and aid of US Human Plans Committee et in identifying candidate human landing sites al., 2009; , 1969). In lieu of a formal and hazard avoidance. Preparation for human Mars+ program, human cislunar exploration exploration will utilize new scientific data for programs, such as the International Space Sta- short-term mission needs (such as site charac- tion (ISS) and , lay the groundwork for terization) and for longer-term exploration an eventual . Many of (such as resource availability mapping and the technologies, industrial infrastructure, dust-storm behavior). flight systems, processes, and operations devel- oped for cislunar exploration will be directly or New science investigations, such as under- indirectly extensible to Mars. We identify sev- standing the dust cycle and the formation of eral areas in which there could be substantial low- ice deposits, can support planning synergy between the human and robotic Mars of human exploration activities, and the power programs. and communications infrastructure needed to support humans at Mars can significantly im- Potential for Significant Collaborative Value prove data return for years to come. And as the most recent decadal survey (NRC, 2011) notes, Between Human and Robotic Mars Programs “Although humans are not required for the re- turn of samples from the Moon, , or Human and robotic exploration of Mars are highly synergistic with each other. The robotic Mars, if humans are going to visit these bodies, collecting and returning high-quality samples program can characterize aspects of the envi- ronment, knowledge of which is necessary for are among the most scientifically important carrying out an eventual human mission; iden- things they can do.” tify in situ resources that can support human Humans can more efficiently identify sci- missions; and develop the scientific back- ence of opportunity; conduct detailed in situ or ground that will inform human missions and laboratory analyses (e.g., geochronology, life provide the intellectual underpinnings for the detection); and operate complex machinery human scientific exploration of Mars. The hu- such as large drills. The enhanced mobility of- man program, in turn, provides the immediacy fered by human missions will expand science for carrying out a robust and vigorous robotic opportunities to previously inaccessible re- program now; allows us to identify areas that gions of Mars. Human missions will return in- require additional information and insights; valuable sample suites for study on Earth, and and, when carried out, will do incredibly valu- human-exploration assets will enable increased able science. data return bandwidth for long-term science use. Technology demonstrations on robotic Scientific robotic exploration of Mars has benefitted—and will continue to benefit—a spacecraft, such as those carried on the Mars

19 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target 2020 Perseverance rover, are of enormous exploration and science overlap, they are not value to human mission planners, whose mis- always identical in detail (e.g., in situ resource sion concepts can benefit from the subsequent utilization wants to know how shallow the top maturation of these technologies. of the ice is; science wants to know how deep the bottom is and why the ice is there). Good Robotic-Human Program Collaboration communication between the programs is Requires Prioritizing Filling in Science Gaps needed, even when the objectives are overlap- ping. One role of the robotic Mars exploration The build-up of infrastructure to support program over the next decade is to fill in our exploration by humans based on the Martian Martian science knowledge gaps and, as with surface will benefit science data return as well cislunar exploration, pave the way for eventual and robotic science missions can add to the human Mars missions. As noted in the most re- communications and atmospheric monitoring cent decadal survey (NRC, 2011), robotic and activities. Just as on Earth, and climate human exploration of space should be synergis- observations and models will have applications tic as both approaches drive the development of to human activities on Mars and in its atmos- new technologies to accomplish objectives at phere. new destinations. The most recent MEPAG science goals Planetary Protection Challenges of Human document (MEPAG, 2020) contains substantial Mars Missions overlap between scientific and human explora- tion goals for Mars. These topics highlight fun- Human exploration of Mars is not without damental knowledge gaps that span the range its significant challenges. One such challenge from atmospheric processes to crustal geophys- is the definition and implementation of appro- ics and satellite properties. However, ambigu- priate Planetary Protection (PP) requirements. ity with respect to specific human-mission ar- Although current low-Earth orbit/cislunar hu- chitecture has prevented prioritization of these man exploration programs advance many oper- knowledge gaps to optimize return for both sci- ations needed for a human Mars program, PP ence and human exploration. An eventual hu- requirements for Mars are likely to be signifi- man Mars mission will likely have multiple ob- cantly different from those implemented for the jectives (e.g., , resource extrac- Moon; this is especially the case given the more tion, exploration, science) that will impact key stringent planetary protection-classification factors like landing site selection, exploration category for all of Mars than for any place on strategies, and habitat design, so understanding the Moon. Techniques used to sterilize robotic the relative priority of each will help optimize missions cannot be used on humans or their robotic science decisions in ways that also sup- food, for instance. port an eventual human mission. Important NASA recently reiterated its commitment work is ongoing now via the Subsurface Water to mitigating both forward and backward con- Ice Mapping (SWIM) activity (Morgan et al., tamination related to human missions in NASA in press; Putzig et al., 2020) to identify the Interim Directive (NID) 8715.129. The NID es- probable locations of near-surface ice deposits tablished a path forward wherein knowledge that may help to provide water and fuel for hu- gained from the ISS, Gateway, lunar surface man missions. Future missions will have to operations, and robotic missions to Mars will “prove out” the existence of the resources to be be leveraged to prevent harmful forward and utilized. Even when objectives for human backward biological contamination.

20 Mars, the Nearest Habitable World October 2020 MASWG II. Mars: A Compelling Target II.G International and Commercial Commercial entities, such as Space Explo- Players ration Technologies Corp., or SpaceX, have also announced intentions to take humans to Mars has become a destination for several Mars and to offer transportation of cargo to the international space agencies, including ESA Red Planet similar to their contractual role for ( [MEX], ExoMars Trace Gas Or- the ISS. A model for this is NASA’s Artemis biter [TGO], and the ExoMars Rover and Sur- Program, which envisions that both it and its face Platform that has been delayed until commercial partners will play critical roles in 2022); the Japanese Exploration the transportation of robotic craft and of astro- Agency (JAXA: , Martian nauts to/from the lunar surface and the stations eXploration/MMX); the Indian to be established there. As noted earlier (Sec- Organisation (ISRO: Mars Mis- tion II.F), with the experience gained at the sion/MOM); the United Arab Emirates Space Moon, Mars would be the next destination for Agency (UAE SA: humans to explore in situ. Many of these plans [EMM]); and the National Space Ad- for the Moon are not yet beyond the aspiration ministration (CNSA: Tianwen-1), in addition stage, but procedures are being developed, to NASA and the Russian State money is being spent, and hardware is being Corporation for Space Activities. In July 2020 built for a 2022 launch. The lunar program has alone, three missions were launched to Mars: been organized and participants selected. To- EMM (Hope), Tianwen-1, and Mars 2020 gether, with independent commercial activities, (Perseverance). there is much to be learned about this new way The opportunities for collaboration and op- of doing business. One should not forget that timization of activity with respect to Mars are Mars poses different challenges than the Moon, clear. Sharing data for the scientific under- but also its own opportunities for enabling hu- standing of Mars and for planning future mis- man exploration and perhaps established pres- sions would be beneficial to all, as would en- ence on another world. suring that the proper infrastructure is in place to return the data acquired and to mitigate risk for all. However, this will require work.

Artist’s impression of two visions for the early Martian climate: a warm and wet planet with on the left, and a cold and icy planet with more limited liquid water on the right. Modern research suggests early Mars may have transitioned between these states, perhaps repeatedly, in its first billion years, although many questions about the nature of the early climate remain to be answered by future missions. (Credit: Harvard )

21 Mars, the Nearest Habitable World October 2020 MASWG III. Findings

III. Findings

MASWG findings are conclusions about Finding 1: Scientific objectives at Mars. the Mars program based on the inputs we’ve re- Many of the most compelling scientific ceived and the combined experience and par- objectives needed to address planetary ques- ticipation in the Mars program by the MASWG tions (including for exoplanets) can be most members. The findings summarize our current effectively achieved at Mars, and a coherent understanding of the science of Mars, the ac- Mars program is required to make the best cessibility of Mars for both human and robotic progress on those objectives. exploration, the role of MSR, the sizes of Rationale: As described in Section II, ex- spacecraft missions necessary to carry out sci- ploration of Mars allows significant insights ence and exploration, the specific potential util- into planetary formation, impact bombardment, ity of small spacecraft, the role of commercial interior and crustal processes, atmospheric and enterprises or commercial-government partner- climate evolution, and potentially the origin ships, the value of international collaboration and evolution of life on a habitable planet. in the science and missions, and the relation- Having the entire 4 billion-year-plus history of ship between the human and robotic explora- Mars accessible in different locations allows tion programs. determination of how these processes have op- On this last point, MASWG had considera- erated and how they’ve interacted with each ble difficulty in defining terms that relate to the other through time. While other objects in our distinction between human and robotic explo- solar system contain a record of many of these ration. This terminology is inadequate because processes, Mars is the only one that has access the science, mission objectives, and implemen- to the full range of processes throughout its en- tation do not divide easily. The division is not tire history. Any understanding of how they’ve unique, whether we categorize by “human ex- operated elsewhere in the solar system will, of ploration” versus “robotic exploration,” by necessity, have to come back to comparison “human missions” versus “science missions,” with how they’ve operated on both Earth and or by missions carried out by the Human Ex- Mars in order to enhance our understanding of ploration and Operations Mission Directorate planetary evolution. (HEOMD) at NASA versus those within the Mars also provides the strongest insights Science Mission Directorate (SMD), and there available into the evolution of key aspects of are gray areas between every categorization. exoplanets. Earth, Venus, and Mars span the Here, we’re going to use “human program” or range of planet size and show the effects in dif- “human exploration” to mean spacecraft mis- ferent combinations of solar insolation (i.e., sions that carry humans to Mars as a core activ- distance from Sun), size, volatile inventory and ity or that directly support them, and “robotic interactions with an atmosphere, and presence program” or “robotic exploration” to mean or absence of a . In particular, a missions that utilize non-crewed spacecraft that major question about exoplanets is the evolu- carry out scientific investigation of Mars. tion of their atmospheres and potential habita- Awareness of the synergies and gray areas bility. Mars’ interactions with the Sun and the highlights the need to more clearly define the solar have driven significant loss of vola- HEOMD and SMD roles in their complemen- tiles and change in climate, and the processes tary efforts. Doing so would further enable an responsible for this at Mars are being explored SMD-based Mars program to coordinate ef- in order to understand the ramifications for forts with the HEOMD that build on the strate- planets around other stars. gies and strengths of a Mars program.

22 Mars, the Nearest Habitable World October 2020 MASWG III. Findings Understanding all of the different compo- inform our understanding of the long-term loss nents of the Mars environment cannot be done of atmospheric gas to space and the evolution with a single spacecraft mission—each mission of Mars’ climate. The coupling between the at- sent to date, making different but complemen- mosphere and the polar caps similarly informs tary measurements, has revealed major new our view of how the climate processes have op- perspectives of Mars and has made fundamen- erated on various timescales over the last 10 tal discoveries about the planet. Even though Ma, of how those processes extend to longer we are asking more sophisticated questions that timescales, and of how the polar caps may re- will require more detailed measurements, we tain a record of on Mars. do not expect that this period of discovery is The seasonal cycles combine to produce over. Addressing the fundamental questions changes that are observable on the surface to- about Mars will require a series of missions that day. These include formation, changes in, and explore the upper atmosphere, lower atmos- removal of dust streaks on the surface; the phere, surface, polar caps, and interior of the movement of sand dunes; and changes observ- planet. These areas are not unconnected to able in the polar caps both in the CO2 deposits each other, however. The missions addressing and the exposed layers. All of the processes we these components will need to be complemen- observe today, operating at timescales from tary to each other, both to ensure that they don’t minutes to centuries, affect our understanding duplicate measurements and also to ensure that, of the behavior of the entire system throughout together, they span the range of needed obser- Mars’ history. vations. Missions will need to be coordinated Evidence for additional processes that are with each other in a way that ensures that the likely to be operating today is seen in the gul- connections between different areas are ex- lies (which are small enough that it is unlikely ploited rather than falling through the cracks. that they could be ancient features that have This can be done most effectively within the survived to the present) and the recurring slope construct of an overall program of Mars explo- lineae (which are observed to form and evolve ration rather than as a series of unconnected throughout a Mars year). Whether these relate one-off missions. A more detailed rationale is to the transient or intermittent presence of liq- given in Section IV.A. uid water at or very near to the surface, and their relationship to deliquescent minerals that Finding 2: Mars as a dynamic planet. can allow liquid water to be stable in small Two decades of exploring Mars from or- quantities at the present, for example, is not bit and on the surface have revealed a cur- clear and requires further elucidation. rently dynamic planet with a diversity of an- The incredible ancient and modern rock cient environments, many with the neces- and volatile record preserved at Mars provides sary conditions for habitability and contain- an unparalleled opportunity to understand the ing clues to their evolutionary history. origin and history of the solar system and the Rationale: Mars today is a dynamic planet. potential for life beyond Earth. That extensive As we explore in more detail, we are finding and diverse rock record is exposed and accessi- that the atmosphere has a complex seasonal and ble on the surface today. The rock and atmos- interannual interplay between the atmospheric pheric record can tell us about the history of cli- circulation, the CO2 cycle, the dust cycle, and mate change and the coupling between geolog- the water cycle. The lower atmosphere that ical, atmospheric, and potentially biological contains the major effects of these cycles con- processes. The global analyses from orbit and nects to the upper atmosphere, where observa- the local analyses carried out by landers and tions of the processes that are ongoing today rovers tell us that Mars has all of the ingredients

23 Mars, the Nearest Habitable World October 2020 MASWG III. Findings necessary to support life and that the chemical atmosphere-surface-subsurface interfaces and environment has been conducive to the pres- at the exobase—is needed to have a complete ence of life—that Mars has been habitable by understanding and to be sure that our models of microbes throughout a large fraction of its life, processes are adequate such that extrapolation and that it’s a reasonable question to ask into past environments (e.g., a faint young Sun, whether life actually has been present. a different atmospheric composition) will illu- The Martian subsurface, with its clues to minate fundamental questions of planetary the formation of the planetary crust and interior change. and as a possible refuge of extant life, is largely unexplored. The basic division into a crust, Finding 3: Complete and accessible record. mantle, and core is poorly determined at pre- For both science and exploration by hu- sent; understanding the differences from Earth mans, Mars has the compelling advantages and Venus will be important for determining of being the most easily accessible planet by the factors that control formation and evolution both robotic and human missions and re- of terrestrial planets. The complex geology ob- taining a record of its geological, climate, served by rovers at the surface tells us that the and perhaps biological history throughout processes responsible for forming the surface time. have been as complex as on the Earth. While Rationale: Among the compelling charac- measurements tell us about surface ice and ice teristics of Mars as a target for science and hu- within the top few meters of the surface at in- man exploration, the most striking are the lon- termediate and high latitudes, we do not know gevity and apparent completeness of the geo- how deep the ice layer extends or whether there logic record exposed at the surface or in the is a liquid water-rich layer beneath it in the near-surface. This record spans the evolution crust. If such a layer is present, it could be the of this habitable planet from its origin through refugium in which life could exist even up a period of sustained surface habitability to its through the present. detection is still current geologically active but uninhabitable in dispute, yet gases measured at the sur- surface and potentially habitable subsurface. face may be our best window into subsurface The record locked into the geologic deposits on habitability and the possibility of extant life. the surface is accessible by orbital and landed The existing understanding of Mars’ di- spacecraft. With continued technological de- verse environments and the capability to ob- velopment, remote access to the third dimen- serve interconnected processes at multiple tem- sion, the subsurface, is imminent. It is easily the poral and spatial scales leaves Mars uniquely best place in the solar system to study the first suited for a systems-science approach. Mars is billion years of the evolution of a habitable ter- presently the only place beyond Earth that can restrial planet. This record has been severely be viewed through this lens. A program will be degraded on Earth and has been erased or is not required to coordinate the observing strategies accessible on Venus, and the ancient terrains and campaigns required to realize the full po- preserved on the Moon and Mercury provide tential that Mars offers in this regard. While little insight into atmospheric evolution, water, we have characterized many aspects of the at- and habitability. mosphere and surface, detailed examination of The beauty of Mars’ accessible record is the processes is very much needed if we are to that it encompasses fundamental planetary understand how and why changes have oc- transitions, from the time when the surface be- curred over time. That detailed study of pro- came geologically stable (pre-Noachian), to a cesses—of transport, of photochemistry, of planet that supports liquid water on the surface volatile transformation, of exchange at the (Noachian), through an intense period of global

24 Mars, the Nearest Habitable World October 2020 MASWG III. Findings volcanism and declining habitability (Hespe- this objective is currently underway, initiated rian), to a planet dominated by cold and dry by the launch of the Perseverance rover on July surface conditions (). While Mars 30, 2020, and continuing with preparations for was once undeniably habitable by microbes at retrieval of Perseverance’s cached samples for the surface, that is no longer the case (except return to Earth. Perseverance will land in possibly in isolated or intermittent locations), Jezero Crater on Mars in February 2021, a land- and this record of multiple transitions is acces- ing site that was carefully selected through a sible to robotic and human explorers. Our un- multi-year effort that included input from a derstanding of the presents im- large community of planetary scientists utiliz- portant issues. While the modern cold and dry ing orbital remote sensing and landed experi- Mars climate can be modeled with some cer- ence. tainty, making the planet’s climate warm Jezero Crater was selected as the landing enough to support sustained liquid water at the site for Perseverance owing to its high poten- surface 4 billion years ago when the Sun’s out- tial for scientific return. A key feature of put was 25% smaller is problematic. Yet the Jezero is that it hosts water-transported geologic evidence from orbiters, landers, and deposits which may retain evidence of ancient meteorites is unequivocal. The keys to unlock- Martian life or its organic precursors. In addi- ing this mystery are available in the accessible tion, the landing site provides opportunities to geologic record through the physical-chemical examine a diversity of materials that will in- records of its early history (rock and sedi- form a substantially deeper understanding of ments), of the recent geologic past (ice and Mars geologic and climate history. Analysis of dust), and of the long-term evolution of its at- these materials will provide new constraints on mosphere (gases and their isotopes), some of the potential for life in the solar system, the his- which are no longer accessible even on Earth. tory of impact and magmatic processes, the The of Mars and Earth make Mars timing and duration of liquid water on the Mar- readily accessible to robotic and human explor- tian surface, environmental conditions during ers from Earth on a regular basis when the plan- alteration and diagenesis of Martian rocks, and ets align properly in their orbits. This occurs many other areas. every ~26 months, with travel times between Return of samples from Mars to Earth will the two planets of 6–9 months. These charac- provide an unprecedented opportunity for de- teristics make it possible to construct sequences tailed examination of materials from another of missions that build off the results and planet and will doubtlessly lead to significantly achievements of past and ongoing missions to improved understanding of both Mars and the achieve a compelling architecture of explora- solar system in general (Mustard et al., 2013). tion. The ability to study the materials in terrestrial laboratories using state-of-the-art instrumenta- Finding 4: Completion of Mars Sample tion with multiple complementary methodolo- Return. gies will allow for acquisition of information The MSR program will produce a major far beyond what would be possible with landed step forward in planetary science and should spacecraft. Among the many potential out- be completed as planned. comes are a detailed characterization of the Rationale: The Visions and Voyages Plan- composition and distribution of organic com- etary Sciences Decadal Survey for 2013–2022 pounds and other potential biosignatures, identified sample return from Mars as the high- highly accurate age dating of geologic events, est priority Flagship mission for the advance- and fine-scale measurements of chemical ele- ment of planetary sciences. Implementation of ments, , and isotopes that will lead

25 Mars, the Nearest Habitable World October 2020 MASWG III. Findings to highly refined interpretations of geologic (e.g., MSR). The point is that a program can be processes. most effective when the mission class is Whatever the results tell us about the geo- matched to the science objective, while remem- logical and biological history of Mars, it will bering that a few small missions might answer represent a leap forward in our understanding the science need traditionally addressed by a of our nearest neighbor planet. We reaffirm the large mission and might do so more cost-effec- value of completing MSR as an extremely high tively. To realize this potential (Section IV.B), priority for Mars exploration and planetary sci- timely investment in the technological ad- ences. vancement will be needed (e.g., Finding 7). Figure III-1 shows the mapping of mission Finding 5: Utilize all mission size classes. class to some of the key measurements identi- A Mars program can most effectively ad- fied above (with SSc, DSc, NFc, and FLG de- dress the full range of key science objectives noting Small Spacecraft, Discovery, New Fron- by appropriately utilizing missions in all size tiers, and Flagship class, respectively). Where classes, in addition to MSR. The key is to several classes are indicated as addressing the match the mission class to the science objec- key measurement, this is often a case of follow- tive. ing up on an initial discovery by utilizing Successful NASA Mars missions have in- greater capabilities (e.g., more coverage, better cluded Flagships (Viking, ), New resolution, increased sensitivity, or a refined Frontiers Class (Mars Exploration Rovers approach). Again, the key is to make the right [MER], Mars Reconnaissance Orbiter [MRO]), choice of mission class for the objective, par- Discovery/Mars /smaller directed mis- ticularly in an integrated program where mis- sions (, Mars Odyssey Orbiter sions can build on one another (e.g., finding the [ODY], [PHX], Mars Atmosphere and right site for a landed investigation). Volatile EvolutioN [MAVEN], InSight), and small spacecraft ( [MarCO]). Finding 6: Small-spacecraft technology. The range of capabilities flown was required to Rapidly evolving small-spacecraft tech- address the mission science objectives, which nologies could enable measurements that required orbital remote sensing and landed pay- address many key science objectives at loads, some with mobility. Fundamental sci- Mars. This class of missions could become ence can be done with missions that span costs an important component of robotic explora- from Small Spacecraft class ($100M–300M in tion of Mars by enabling a higher cadence of full life-cycle cost) to Discovery- or New Fron- scientific discovery at affordable cost. tiers-class (up to $1.25B). A robust Mars Ex- Rationale: The last decade has seen grow- ploration Program also should utilize missions ing capabilities of small spacecraft in Earth or- of all size classes, tailored to the challenge of bit and beyond for commercial, defense, and the objectives. An exciting new development Principal Investigator (PI)-led scientific mis- is the rapid advance in small-spacecraft tech- sions. The term “small spacecraft” encom- nologies and in miniaturization of instruments, passes a range of concepts but is commonly already in play for Earth orbit, raising the pos- considered to be spacecraft having a mass of sibility that high-priority science can be less than about 500 kg. Small spacecraft can in- achieved at more affordable cost (see the next clude instrumentation within impactors (e.g., finding and Section IV.B). Clearly, small Mars landed mission ballast mass), spacecraft cannot address all of the major sci- deployed by a spacecraft at the destina- ence questions (Section V), so the larger or tion, small that launch as rideshare more expensive missions have their role to play secondary payloads and independently proceed

26 Mars, the Nearest Habitable World October 2020 MASWG III. Findings

Figure III-1. Traceability match from science goal mission element to Small Spacecraft (SSc), Discovery (DSc), New Frontiers (NFc), and Flagship (FLG) class missions. The numbers in the M-Arc column refer to the mission “arcs” (sequences of mission types) defined and described in Section VI.B. to the destination, or independently launched spacecraft during sample return is provided in spacecraft that take advantage of emerging Section IV.B. small launch capabilities. Finding 7: Affordable access to the surface. We will use the term Small-Spacecraft A critical scientific need for Mars explo- class (SSc) to mean spacecraft having a full ration is affordable access to multiple places life-cycle cost in the range of ~$100M–300M. on the Martian surface with adequate pay- SSc using present-day technology/capabilities load/mobility to make the measurements could make high-priority scientific measure- that would revolutionize our understanding ments from orbit (e.g., for study of atmosphere of the Mars system. processes and climate). They could also pro- Rationale: The Mars program has reached vide a platform for other types of science meas- a point where many of the most pressing meas- urements (e.g., network landers for , urements for key science topics can only be ad- subsurface ice detection, or boundary layer dressed in situ (see Figure III-1). These include processes) utilizing technologies that could be (see Sections II.E and VI) ancient environmen- developed in the next 5–10 years. Small-space- tal diversity (cm-scale petrology and stratigra- craft capabilities relative to cost, requirements, phy), modern climate variability (cm-scale and performance need to be addressed pro- analysis at the polar caps), biogeochemical cy- grammatically to realize their full potential. cles (isotopic measurements of volatiles in Existing challenges to implementing Mars rocks), solar system chronology (in situ iso- small spacecraft science missions include early topes), and life detection (in situ organics) identification of rideshare launch opportunities (e.g., Ehlmann et al. [2016]). Our growing as well as enhanced technological capabilities knowledge from orbiters has pinpointed key lo- in the specific areas of propulsion, communica- cations that in several instances (e.g., ancient tion, and entry descent and landing. More detail environments exploration, geochronology) on the programmatic opportunity of small

27 Mars, the Nearest Habitable World October 2020 MASWG III. Findings require either precision landing or extended private entity bears a reasonable fraction of mobility. the investment risk, do not yet exist. A suc- In the post-Viking era, Mars landed mission cessful Mars-focused, CLPS-like program costs have escalated at each launch oppor- might serve as a programmatic to al- tunity. While the MER missions (Spirit and low—at reduced cost but perhaps increased Opportunity) were executed at close to New risk—development of technologies for fu- Frontiers class (~$1.1B for two rovers in ture exploration as well as delivery of sci- FY20$), roving or drilling are now perceived ence payloads. as and costed as being Flagship-level engineer- Rationale: As outlined in presentations to ing challenges. Mars surface access cannot the Decadal Midterm Committee and to presently be accomplished in the Discovery- MASWG, NASA is open to innovative ideas class cost cap without significant reuse of hard- and partnerships. However, purely commercial ware (as with the PHX mission) or a fully non- or public-private partnerships for deep space NASA contributed payload (InSight), and com- are relatively rare, and none for Mars has yet petition rules now preclude more than 30% for- succeeded. NASA’s 2014 Request for Infor- eign payload contributions. Consequently, mation (RFI) for Mars Communications has even traditional Mars landers may no longer be not borne fruit. A particularly provocative ex- possible in Discovery. The loss of capability to ample was given during the MASWG open conduct landed science within competed mis- fact-finding sessions, where we received a sion classes contrasts with the criticality of presentation from a SpaceX representative, landed science for our understanding of the who asserted that the SpaceX might be Mars system. investments able to transport cargo to Mars as early as 2022 in reducing the cost for access to the Mars sur- and humans by 2024. Despite the exceptional face would be a game changer for the quality success of the and Dragon and diversity of science possible at SSc-, Dis- launches, sending a Starship to Mars within covery-, and New Frontiers-class missions at two years appears to be an aspirational goal for Mars. a process that may take a few attempts to get it Lower cost, repeatable technology for sur- right. Even so, leveraging commercial ap- face landing and mobility at Mars to enable proaches at Mars that are extensions of industry high-priority in situ science is crucial for the capabilities being developed for other purposes Mars program, allowing the program to address in space may be promising ways to engage the diversity of the surface record of geology partners in the technology developments and climate, unravel processes driving the evo- needed for Mars orbiters and landers. lution of habitability, and search for life. There The programmatic core of the CLPS pro- may be an opportunity to leverage technolo- gram is an IDIQ (Indefinite Delivery, Indefi- gies, work with commercial providers, or use nite Quantity), competitively awarded, fixed- contracting approaches derived from the Com- price contracting process. As described in Sec- mercial Lunar Payload Services (CLPS) pro- tion II and in numerous studies that preceded gram in facilitating lower cost access to the this one, there is an abundance of science both Martian surface (see Section IV.C). beyond and complementary to MSR that should be conducted in order to fully under- Finding 8: Commercial activities and stand Mars. The challenge is to keep the cost potential partnerships. constrained while maximizing the potential for Purely commercial or commercial-gov- mission success. Given the expansion in the ernment partnerships for exploring or sup- number of space entrepreneurs, the current suc- porting the exploration of Mars, where the cess of CRS (Cargo Resupply Services, via the

28 Mars, the Nearest Habitable World October 2020 MASWG III. Findings ) and various low- include the , ESA, Japan, India, Earth orbit (LEO) and , China, and the United Arab Emirates. (GEO) ventures, examining the possibility for With this interest, the potential exists for col- such an initiative appears to be very timely and laboration and coordination as a way of in- reasonable, perhaps via an RFI or workshop creasing the amount of science that can be done process. An important element of this study and decreasing the cost to individual countries. would be to identify a business case that would The continued exploration of Mars is ex- provide the impetus for entrepreneurs to invest. pected to involve more complex and capable Might specific hardware developed for the platforms but also constellations of smaller, Moon be well-suited to Martian environments? simpler spacecraft. The anticipated greater An additional consideration is whether the ca- costs of such endeavors added up over all mis- dence to Mars required to be commercially vi- sions, particularly within the framework of a able is sufficient and whether interleaving with dedicated Mars Exploration Program, will re- similar requirements for lunar or ex- quire a continued framework of international ploration is sufficiently synergistic. More detail cooperation. A prime example of this need on these issues is provided in Section IV.C. may be found with the MSR mission itself, in which both NASA and ESA are providing ma- Finding 9: International collaboration. jor components of the missions. However, ef- There is tremendous value in developing forts should also continue along the lines of the collaborations between the many different coordination and collaboration activities dis- governments and entities interested in Mars cussed above, particularly given the expanded exploration. opportunities envisioned by other findings and Rationale: The exploration of Mars over recommendations found in this report (cf. po- the past two decades has involved many exam- tential Mission Arcs in Section VI). A particu- ples that highlight the benefit of collaboration lar need to enable small spacecraft at Mars and of coordination of activities between inter- would be for the program to identify as early as national partners. Such joint efforts encom- possible rideshare (launch) opportunities pass a range from the simple, but highly bene- among all public/private providers and to de- ficial, planning of observations to facilitate op- lineate requirements and timing, including the portunities for extended observational cover- release of mass margin for secondary payloads age and communication relay, to the contribu- by international and commercial entities, and to tion of instruments and personnel. Examples retain flexibility against changes in the primary of the former include overflights and commu- mission that would affect rideshare opportuni- nication passes between NASA-landed assets ties. and ESA’s TGO, while recent examples of the latter involve NASA-funded U.S. investigators Finding 10: Connections with the human for TGO and European instrument contribu- Mars program. tions to the InSight mission. While these ac- The scientific and the human explora- tivities have traditionally been guided by the tions of Mars are inextricably intertwined. principle of “no exchange of funds,” the scien- Addressing science objectives will be an in- tific return from these international collabora- tegral part of upcoming human exploration, tions has been of tremendous value to all part- and preparing for future human exploration ners. provides one of the rationales behind having As noted in Section II.G, there are an in- a vigorous robotic Mars scientific explora- creasing number of international players in tion program today. Mars exploration. Participating entities now

29 Mars, the Nearest Habitable World October 2020 MASWG III. Findings Rationale: There is potential for significant efforts to define gaps in our understanding of value in collaboration between the human and the Mars environment that would be of high robotic science Mars programs. The scientific value to fill prior to committing to architecture and the human exploration of Mars are inextri- or design for human missions. It’s not clear cably intertwined. Addressing science objec- which knowledge gaps must have better defini- tives will be an part of upcoming hu- tion prior to human missions, which are “nice- man exploration, and preparing for future hu- to-haves,” and which do not need to be ad- man exploration provides one of the rationales dressed. Such a prioritization is necessary in behind having a vigorous Mars scientific ex- order to define an orderly suite of missions or ploration program today. Measurements that instruments that can address them. support planning for robotic exploration also Forward and backward PP challenges of can support the scientific exploration by hu- human Mars missions are anticipated to drive mans on Mars, and vice versa. Such measure- additional science needs. With humans in- ments include, but are not limited to, the need volved, it’s not possible to keep contamination to understand current environmental conditions entirely out of the Martian environment. prior to sending humans, the search for acces- NASA’s current PP requirements were not de- sible resources that can be utilized by humans, signed to deal with the difficulties of human and the definition of scientific questions ame- missions. With the goal of PP being to support nable to exploration by human missions. Dis- the science, requirements have to be realistic coveries are being made today that are signifi- enough to not preclude human exploration at cantly changing our understanding of the Mar- the surface yet not compromise the science sig- tian environment and resource availability and nificantly. We understand that NASA is in the thereby impacting our ability to carry out hu- process of defining PP requirements for the era man missions. We expect such discoveries to of human exploration. Here, we note that these continue in the foreseeable future, requiring in- are significant issues that must be addressed in teraction between the exploration directorates a timely manner. We have the expectation that for science and for human activities PP for both human and robotic missions will The potential for significant value requires evolve substantially over the coming decade. a better prioritization of science knowledge Detailed discussion of the PP issues is provided gaps relevant to human Mars exploration. in Appendix B. There has been insufficient interaction to date between the human and the robotic Mars explo- ration programs. This appears to be hampering

30 Mars, the Nearest Habitable World October 2020 MASWG III. Findings

The Perseverance rover in the clean room at the Jet Propulsion Laboratory, Pasadena, CA. The rover is now on its way to Mars, where it will land on , 2021. The rover carries a as a technical demonstration, a device (MOXIE) to demonstrate the feasibility of producing oxygen from the atmosphere as a possible in situ resource capability for human explorers on Mars, and a suite of science instruments for in situ science and the preparation of samples drilled from the Martian surface for possible return to Earth. (Credit: NASA/JPL)

31 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities

IV. Programmatic Rationale and Future Opportunities

the development of rover technology and oper- IV.A Why a Mars Program is ations. The first was the Necessary rover aboard the Mars Pathfinder, one of the The question of why a Mars program is first Discovery missions. Sojourner was necessary to support the continued exploration roughly the size of a oven and of Mars splits into two parallel questions: what demonstrated the ability to traverse over the are the functions of a separately identified pro- surface; the science value of using it was small. gram that can provide support for Mars explo- However, it led directly to the development and ration beyond individual missions, and why is operations of the MER Spirit and Opportunity. having a program necessary to support the ex- These were larger, were well instrumented, and ploration? We considered each of these. had operations involving substantial traverses and detailed exploration of multiple geological Functions and characteristics of a Mars pro- sites. Following that, the Mars Science Labor- gram. atory (MSL) Curiosity rover was larger still, with a more sophisticated payload and a longer The value of having a separate program to planned life; traverses were planned and car- support Mars missions is its ability to carry out ried out, were more complex, visited more functions that lie outside of an individual mis- sites, and carried out more detailed scientific sion and that affect more than one mission. analysis at each site. Each rover was more so- Currently, a Mars Program Office exists at phisticated and more complex than those pre- NASA’s Jet Propulsion Laboratory (JPL) that ceding it and had more involved operations al- oversees the various components of the pro- lowing significant scientific results to be ob- gram. The key functions of a program are tained. Without the ability to develop the listed in Table IV-1. rover, sampling, and operations capabilities on One example that shows the value of a pro- successive missions outside of the develop- gram in supporting Mars exploration deals with ment of an individual mission, we would not Table IV-1. Functions of a Mars Exploration Program.

• Allows coordination and continuity between missions to achieve science objectives beyond what a single mission or even a series of one-off missions could accomplish • Provides feed-forward between missions on both science and technology, including use of small spacecraft as proof of concept for innovative approaches or measurements • Allows development of infrastructure that can serve multiple missions (e.g., communications relay from orbit, landing-site characterization and certification using high-resolution imag- ing) • Allows effective negotiation and coordination with international and commercial partners to take advantage of the tremendous interest in exploring Mars • Allows focused development of required spacecraft and instrument technology in advance of mission selection (e.g., Mars Ascent Vehicle [MAV] development for MSR, PP concepts or implementations) • Allows coordination between SMD and HEOMD to ensure strong connections between the human and robotic programs for Mars

32 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities have been able to implement these missions in of objects. For Mars, the justification for hav- a timely manner. ing a program falls into three areas—scientific, A second example involves the use of Elec- programmatic, and exploration: tra communications relay on Mars orbit- • Scientific: Mars provides the opportunity to ers to provide communications between explore the full range of processes and prop- landers and rovers on the surface and Earth. erties on terrestrial planets under different Without such communications relays, the capa- boundary conditions from Earth, including bility to return data from the surface would be interactions between geological, geophysi- more than an order of magnitude smaller and cal, climate/atmosphere, , and the science return from surface missions would potential biological processes. The science be significantly reduced. The Mars Explora- spans a much wider range of topics (and re- tion Program office at JPL provides coordina- quires a wider range of measurements) than tion in the procurement and integration of the can be accomplished by any single space- equipment on the orbiters and in the craft or mission. Two aspects of Mars that planning of complex relay operations that cur- uniquely allow exploration of the full range rently span four orbiters and two surface plat- of scientific questions that, in fact, span the forms. terrestrial planets are that: A third example, in the area of advance − Mars’ entire history is preserved in an ac- planning, involves the coordination between cessible rock record that includes the first NASA and the space agencies of other coun- billion years, and tries or commercial entities. This, for example, − Mars has key similarities with the Earth is central to the coordination of hardware de- to allow us to understand the processes velopment and mission operations in collabo- that operated, with enough differences to ration with ESA on the MSR suite of missions. truly test our models and our understand- There are other examples showing the ing. value of having a program, including advance • Programmatic: Mars is accessible enough planning of new missions, development and that multiple missions can be flown to ex- oversight of PP protocols and implementation, plore the different components of the Mars public outreach that is coordinated across pro- environment and their interactions with each jects, development of hardware for future mis- other, including substantial access to the sions (such as the MAV or the Mars helicop- surface. Having a Mars program allows us ter). These are all best carried out in a coordi- to carry out a mission that is focused on one nated way rather than left to development by aspect of the Mars system, knowing that individual missions. other aspects will be addressed in comple- mentary ways on other missions. Past expe- Why is a program necessary to carry out these rience has shown that the Martian environ- functions? mental system is complex and that the dif- ferent components interact with each other; A program is necessary when one is en- understanding these interactions, from the gaged in a series of missions that require: 1) de- deep interior to the upper atmosphere, re- velopment of technological capabilities that re- quires multiple missions that are well coor- quire long lead time for future missions, and/or dinated with each other. 2) coordination between missions, either in op- • Exploration: Mars is NASA’s stated long- erations or on science results that require inte- term destination for human exploration. gration across missions. A program can be de- Precursor spacecraft missions are required veloped for exploration of any object or series in advance of human missions so that we

33 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities can be ready for human missions to Mars, by what we have defined as SSc missions, us- both with appropriate scientific background ing an estimated cost range of $100M–300M and with an adequate understanding of the (see Section III, Finding 5, Section VI.A and Martian environment. Appendix C). From orbit, these include charac- terization of atmospheric circulation and IV.B Small Spacecraft for Mars: A transport processes over multiple Mars years, Programmatic Opportunity low-altitude magnetic and gravity-field map- The ongoing rapid development of small- ping, and high-resolution of the spacecraft capabilities (e.g., as described at ancient record of environmental transitions. SmallSat/CubeSat Fleet Missions Database More ambitiously, SSc landers, either deployed [https://s3vi.ndc.nasa.gov/cubesat/] or Small- from larger landers or as standalone small Sat/CubeSat Fleet Missions Graphic landers (once developed), could perform in situ [https://s3vi.ndc.nasa.gov/cubesatfleet/] for geophysics and ice-depth measurements or CubeSat missions) has the potential to provide characterize surface-atmosphere boundary- a new means of exploring Mars with more af- layer interactions that cannot be measured from fordable and more frequent flights of payloads orbit. With lower cost and shorter development for scientific measurements and support of hu- times, SSc can be launched at a higher cadence man exploration needs. Many science objec- than traditional larger missions and can re- tives will still need to be addressed by the more spond more rapidly to new discoveries. To capable Discovery-, New Frontiers-, and Flag- fully leverage these advantages, SSc must be ship-class missions (Section III, Finding 5). planned and implemented through a distinct Even so, extensive use of small spacecraft at Mars program. Competed, PI-led science op- Mars is particularly appealing during an other- portunities will allow the best concepts to be wise MSR-focused decade; such use could add developed and prioritized at selection. The cre- a component to the Mars Exploration Program ativity of the community in developing ideas that achieves high-priority science with fre- and mission concepts that can accomplish com- quent launches at an affordable cost, while pelling science within the structure of small- opening the way for commercial participation. spacecraft missions should not be underesti- mated. The Small Innovative Missions for Plane- tary Exploration (SIMPLEx) mission flight Past SSc at Mars have had mixed success. program and Planetary Science Deep Space In 2018, MarCO successfully demonstrated SmallSat Studies (PSDS3) mission concept CubeSat capability in deep space with two in- study program aim to demonstrate multiple dependent Mars flybys that relayed communi- compelling small spacecraft missions into the cations during the InSight spacecraft entry, de- Mars system at development costs of less than scent, and landing. In 1999, two ~$100M. As an example, the SIMPLEx Heli- microprobes attempted to land as penetrators ophysics mission EscaPADE (in Phase A/B at released from the Mars Polar prior to the times that MASWG was meeting) will ; neither the two probes nor make measurements to understand the interac- the carrier lander were heard from after the tion of the Mars with the solar point of separation. While there are small Mars wind and is being developed within a $55M mission in development (e.g., EscaPADE), cost cap (not including ) (Lillis there is one now on its way to Mars: the re- et al., 2020). Our synthesis of the 55 concept cently launched EMM, in the higher end of the studies submitted by the Mars community (see small spacecraft range defined here, carries a Appendix A) identified several scientific prior- capable payload to observe the Mars lower and ities at Mars that can be addressed effectively upper atmosphere once it enters a novel, quasi-

34 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities areostationary orbit. Its success would be an small missions. Taking advantage of launches early demonstration for NASA and other space from multiple nations planning direct-to-Mars agencies of the viability of the small mission or Mars- missions in the next decade re- approach to achieving compelling science at quires programmatic coordination to identify Mars. the potential specific opportunities or similar The ability to sustain a flight program of families of opportunities, delineate the require- multiple SSc missions requires that an appro- ments and the timing surrounding the confir- priate risk posture be used to ensure a reasona- mation of release of mass margin for secondary ble probability of success for the portfolio as a payloads, determine payload primary inter- whole. This will ensure that the program be re- faces, and coordinate release of this infor- silient to single mission failures. Issues that mation to SSc proposers/providers. With would need to be addressed include: emerging new commercial small-launch capa- • Possible elimination of dual-string systems bilities at moderate cost, there may also be greater opportunities for sending spacecraft to • Tailoring of risk posture with judicious re- Mars from LEO/GEO launches. laxation of some oversight requirements; for example, by conducting mis- Key enabling SSc technology challenges sions as tailored Class D as per NPR 8705.4 are communications, propulsion, and entry- and 7120.5E (as with SIMPLEx and some landing systems, the first two of which are un- dergoing rapid development now. Maintenance Earth Ventures missions) of a communications network at Mars also • Further development of enabling technolo- would be a key SSc enabler. Facilitating infor- gies mation sharing on propulsion capabilities and The viability and cost tradeoffs of Class D needs will facilitate SSc mission design. For or single-string missions for planetary missions small spacecraft landers, there are several (including cost trade-offs) would need to be de- promising, early-stage emerging concepts, but termined separately for each mission’s objec- more work is needed to understand cost-capa- tives; for example, longer-lived small space- bility tradeoffs between velocity at landing, craft could be traded against a series of small precision targeting of a landing site, and mobil- spacecraft to capture climate variability over ity after landing. multiple Mars years, with each approach hav- The Mars program needs to develop SSc ing different requirements. The CLPS program potential by matching spacecraft class and ca- today is pioneering an approach of having pri- pabilities to the mission objectives within a rea- vate companies propose their own designs and sonable risk/cost profile. This could be done having more mission-assurance autonomy (see programmatically by choosing missions in the Section IV.C). Both approaches have potential appropriate size class while integrating them merit for Mars. into coherent program lines that can achieve Key to reducing risk and costs for SSc is the major science objectives. Several example early identification of rideshare opportunities, Mission Arcs are provided in Section VI, each strategic investment in specific technologies, containing between 1 and 5 SSc missions over and examination of planetary protection issues a 15-year period. Such a vigorous contribution and costs (see Appendix B). All Mars and to the Mars Exploration Program would be en- Mars-flyby missions should be evaluated for abled by supportive programmatic actions. rideshare opportunities (including secondary MASWG believes that the current SIMPLEx spacecraft and balance mass) because they cost cap is too low to support a robust Martian would allow the lowest delta-v (and therefore small-spacecraft campaign, but costs in the lowest mass fraction in propellent) option for range of $100M–300M per mission would be

35 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities more appropriate (see Section VI and Appen- sensing satellites and 2) large constellations of dix C). LEO communications spacecraft intended to provide worldwide internet access. The compa- IV.C How to Involve Commercial and nies and investors in these cases vary from International Partners small groups to major entities. However, emerging business enterprise sectors typically Commercial Partnerships: always have a high percentage of new starts and failures. Recently, there have been multiple new en- Currently, deep-space entrepreneurship is trants to the commercial space sector. Often much less common. The best, and so far only, characterized as “new space” or “entrepreneur- example of a current NASA-funded deep-space ial space,” the most visible examples are the initiative with commercial partners is CLPS. NASA-sponsored Cargo Resupply Services The CLPS program is a task order-based IDIQ (CRS) and Commercial Crew Program (CCP) contract for payload delivery services to the for transportation to the ISS, replacing the Moon’s surface, covering payload integration Shuttle. These initiatives began as an experi- and operations, launch from Earth, and landing ment in fixed-price contracting using NASA’s on the Moon. The CLPS contracts presently funded (SAA) authority have a combined maximum contract value of and were known as the Commercial Orbital $2.6B through November 2028. Selected com- Transportation Services (COTS) program. Suc- panies are allowed to bid on specific task or- cessful bidders had to demonstrate substantial ders, which NASA has so far released at a ca- corporate investment. The final selected pro- dence of one every few months. Currently, the viders for CRS contracts ($2B each) were only instance of a purely commercial deep- SpaceX and Orbital Sciences. To date, SpaceX space project of which we are aware is the ap- has provided 16 successful flights and Orbital parent long-term commitment of human travel 10; each company has had one serious mishap to Mars by SpaceX and its founder . in the program. CCP selectees are and In February 2018, SpaceX—using its own SpaceX. These contracts are worth ~$4B for funds—launched the first use of the Falcon Boeing and $2.6B for SpaceX. As of this writ- Heavy, carrying Musk’s personal Tesla road- ing, SpaceX has successfully completed the ster into a Mars-crossing . first CCP flight to and return from the ISS with SpaceX has also embarked on an ambitious a two-person crew. Boeing is planning to plan to develop the so-called Starship, a super- launch its mission in the future. As a measure heavy launch vehicle capable of transporting of the success of this overall approach, a Con- passengers and cargo to Mars. (The Starship is gressionally mandated study of the designed to lift 150 tons to LEO.) development concluded that with a NASA in- In order to continue fostering commercial vestment of <$500M, the Agency has obtained partnerships, we suggest: a new reliable launch vehicle where the devel- opment cost would have been ~$4B under gov- NASA and the Mars community should con- ernment business as usual. tinue to monitor the possibilities and opportu- nities and consider the expansion of shared- In addition to the previous examples, there risk investment in Mars-relevant technologies are multiple entrepreneurs focused on LEO and capabilities. business opportunities. The two initiatives that appear most likely to generate a positive return Currently, purely commercial or commer- on investment (ROI) are 1) large constellations cial-government partnerships for exploring or of relatively low resolution (1–3 m) remote- supporting the exploration of Mars, where the

36 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities

SpaceX Dragon capsule in its first trip to ISS, as an example of the type of commercial-government partnership that can support rapid development. (Credit: NASA) private entity bears a reasonable fraction of the submit realistic fixed-price proposals for spe- investment risk, do not exist. Leveraging com- cific technological capabilities. The industry mercial approaches at Mars that are extensions survey must take into account differences in of industry capabilities being developed for traveling to and landing on the Moon versus the other purposes in space may be promising ways typical 7-month cruise to Mars; the ability to to engage partners in the technology develop- launch to Mars only every 26 months when the ments needed for Mars orbiters (both science- planets align; the much greater challenges of focused and communications-focused) and Entry, Descent and Landing (EDL); and the landers. more stringent Category III, Category IV, or even Category V PP requirements for Mars A successful Mars-focused CLPS-like pro- versus the typical Category I or II classification gram (perhaps Commercial Mars Payload Ser- at the Moon. Another important element of this vices [CoMPS]) could serve as a program- study would be to identify specific hardware matic vehicle to allow development of technol- developed for the Moon that may be well- ogies for future exploration as well as delivery suited to Martian environments. An additional of science payloads. consideration is the cadence to Mars required NASA and the Mars community should for CoMPS to be commercially viable and study the feasibility of adapting the CLPS pro- whether interleaving with similar requirements gram to Mars. The study should include a crit- for lunar or asteroid exploration is synergistic. ical evaluation of whether there are commercial entities that can reasonably be expected to

37 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities International Partnerships: be part of future opportunities, including those described here. There exists a long history of international con- While the failure of a single international tributions to NASA missions, as well as U.S. contribution in coordination or collaboration scientists funded by NASA participating in almost never would result in the loss of the en- missions led by other countries. The specific tire mission or failure to meet minimum suc- details of these efforts would vary, but a few cess criteria, agreements that are interdepend- principles have remained stable across the dec- ent carry a much greater burden. In NASA ades. planetary programs, such interdependence has International efforts typically fall into one been relatively rare. For example, if the ESA- of three categories: coordination, collaboration, provided probe had been lost as it en- or interdependence. Coordination between tered ’s atmosphere, that loss would have missions, where data is shared but there is no compromised the overall mission re- hardware or software interface, have occurred sults, but the Cassini orbiter would not have many times. The ESA MEX mission and been in danger. On the other hand, the German- NASA assets such as MAVEN, Odyssey, and provided propulsion system for the MRO have coordinated numerous times to fa- mission to Jupiter was absolutely critical to cilitate scientific measurements and communi- mission success. Recently, NASA and ESA cations (in addition to actual provision of hard- have publicly defined an approach for MSR ware between countries). One could imagine that is highly interdependent. If the ESA-pro- these missions, the EMM Hope, ESA’s Exo- vided fetch rover or return spacecraft fail to op- Mars, and future projects coordinating in a sim- erate, or if the U.S.-developed MAV does not ilar manner. work, the entire campaign is at risk. Collaboration, where there is typically a We suggest that those key guidelines gen- senior partner and a junior partner, is probably erally should be maintained for the following the most common form of joint effort. For per- MASWG recommendations: haps 50 years or more, there have been instru- • Acquire, maximize, and enhance the best ments developed by other countries contributed science available worldwide. to NASA missions. Radar Imager for Mars’ International cooperation enables the distri- Subsurface Exploration (RIMFAX) and Mars bution of cost and also provides an oppor- Environmental Dynamics Analyzer (MEDA), tunity to find the very best scientists and in- two instruments aboard the Mars 2020 Perse- strumentation at a university or laboratory verance rover, were contributed by interna- outside of the U.S. or NASA. As a conse- tional partners. Most of the instruments on the quence, virtually all of NASA’s Announce- NASA InSight mission were international con- ments of Opportunity (AOs) and Research tributions. Conversely, U.S. teams have been Announcements (NRAs) are open to the en- selected through competitive NASA solicita- tire world, subject to the funding rules. We tions to provide instruments on foreign space- anticipate that this bedrock principle will craft. An additional and common form of col- continue in any solicitations that emerge laboration has been the NASA provision of the from MASWG planning. Deep (DSN) to enable commu- • Establish well managed expectations of nication links with the spacecraft. Typically, budgetary savings, complexity, and out- the barter arrangement of DSN time results in comes. the selection of an instrument provided by a U.S. investigator. Such an exchange could well In the formulation period of any mission concept, there may periodically come a time

38 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities

when the projected cost including reasona- • Define a clean interface between contribu- ble reserves exceeds the available budget. At tions. this point, there are several options: descop- This guideline is required to maintain cost ing (i.e., eliminating requirements); adjust- control, stabilize requirements, and meet ing schedule; or, in some cases, attracting an schedule. The ESA-contributed Huygens international partner who can provide some probe and most foreign instruments that aspect of the mission. A clear-eyed recogni- “bolt on” are good examples of a clean in- tion of what international collaboration can terface. and cannot accomplish is necessary. • Create clarity in the management structure. • Continue “no exchange of funds.” This principle includes procedures for dis- Sovereign states must pay for their own in- pute resolution, processing data, announcing struments, science teams, and other contri- scientific results, conducting the develop- butions. This principle must include support ment engineering, and mission operations. A for any interface management. Such an ap- prime example of this principle has been the proach is usually considered to be a “barter” International . arrangement.

39 Mars, the Nearest Habitable World October 2020 MASWG IV. Programmatic Rationale and Future Opportunities

Left: An example of a deep sedimentary record exposed on Mars on the slopes of Mt. Sharp in Gale Crater, as imaged by the Curiosity rover. Right: Selected events from the geologic history of the first billion years of Mars, including magnetic field cessation, impact ages, and ages for regional units.

40 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations

V. Recommendations

MASWG recommendations are broken into on achieving other high-priority science ob- two distinct components. The first contains jectives, while developing the needed tech- five high-level recommendations about the nologies for going forward. overall nature and structure of a reinvigorated Rationale: Despite the very high science Mars Exploration Program. The second con- value of MSR, it does not address all high-pri- tains 10 additional specific recommendations ority science objectives necessary to give us a that will ensure that the resultant Mars Explo- broad understanding of the evolution of a hab- ration Program can be successful. In each case, itable planet. In order to do this, and to obtain recommendations are given and followed by the necessary knowledge on the Martian envi- elaboration and rationale, as appropriate. The ronment and the science background required structure of a program that will be responsive to support human missions in the next two dec- to these recommendations is discussed in Sec- ades, NASA needs to implement additional sci- tion VI. ence missions. High-priority science objec- tives can be met using the full range of techni- V.A High-level Recommendations cally viable mission classes, from small satel- lites up through New Frontiers-class missions Recommendation 1. and, post-MSR, including possible Flagship- Mars Sample Return should proceed as class missions. The budget necessary to carry currently planned, as it will produce a major out such missions will be discussed in Section step forward in our understanding of Mars, VI. Within funding levels that realistically as envisioned by Visions and Voyages. could be made available, both high-priority sci- Rationale: MSR was the highest priority ence objectives and technology development put forward for a flagship mission in the 2011 necessary for follow-on missions in the next NASEM planetary sciences decadal strategy, decade could be supported. with the understanding that there would be a commitment from NASA to complete the re- Recommendation 3. turn in the next decade of 2023–2032. We For this next phase of Mars exploration, strongly reaffirm that the suite of missions to NASA should retain a programmatically bring samples back should be carried out. The distinct Mars Exploration Program. NASA material in this report is not intended in any should institute mission or budget lines that way to represent an alternative scientific or pro- can allow Mars-specific missions, from small grammatic pathway to carry out sample return. spacecraft through New Frontiers-class mis- It is intended as a proposed program to be car- sions, to be strategically integrated into a ried out in parallel with sample return to ensure program, with missions chosen and imple- that we can obtain a broad and integrated un- mented as appropriate for the science to be derstanding of Mars as a planet. achieved. Rationale: The technology development Recommendation 2. required for future missions, the advance plan- NASA should support missions that ad- ning of missions and their implementation, the dress fundamental science objectives at integration of missions into a program that ad- Mars in addition to MSR, using the full dresses science objectives appropriately, and range of technically viable mission classes. the coordination of missions that allows for During the MSR era, the emphasis should be support between missions can be carried out in

41 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations a robust way only if there is a well-defined will provide the principal focus for the coordi- Mars program that can pursue a long-term vi- nation and integration of cross mission align- sion with independent authority and budget ment and planning efforts with senior staff line. When Mars missions compete against the from the mission directorates, centers, other rest of the solar system in the Discovery and support organizations, and external partners” New Frontiers Programs, they can and have (T. Zurbuchen [SMD Associate Administra- been competitive, but it is unlikely that they tor], personal communication, September 1, will be selected in a manner that is timely for 2020). supporting other missions or that the selected The existence of three separate organiza- science will be integrated with that from other tions that each appear to have some oversight missions in an optimally coherent and coordi- responsibility for different aspects of the Mars nated way. Independence here means having program, and the existence of multiple points the mission or budget lines, authority, and ac- of contact and interaction between the missions countability where planning and implementing that appear to reside within each program, a program can be done within those constraints. leave open the potential for conflicts in the To succeed, it is imperative that sufficient flex- goals and in the explicit requirements and di- ibility be built into the program so that the sci- rections for each program. This is not the first ence to be achieved first be identified and then time that these issues have arisen: In the wake the mission class appropriate for that science of the failures of and selected, rather than defining the mission class in 1999, the final report first and then fitting the science within its capa- from NASA’s Mars Program Independent As- bilities (this applies whether the action is either sessment Team (MPIAT, chaired by A. to expand scope or reduce scope). Thomas Young) stated, “The NASA Headquar- While MASWG was formulating its pre- ters–JPL interface was found to be ineffective liminary results, NASA made two announce- as the result of a failure to clearly communi- ments that affect the structure of the Mars pro- cate. Multiple interfaces at NASA Headquar- gram and bear on this recommendation. First, ters for the JPL Mars Program Manager the next two MSR flight missions were sepa- caused difficulty at both organizations. The in- rated from the rest of the Mars program, with a effective nature of the interface is judged to program director appointed who reports di- have had a negative impact on mission suc- rectly to the SMD Associate Administrator. cess.” MASWG did not have the opportunity While the roles and responsibilities of the MSR to hear directly about these changes, to discuss campaign and the current Mars Exploration their ramifications, or to propose potential al- Program are still being worked out, it is ex- ternative management structures, but we do pected that this new MSR Program will be want to identify these apparent conflicts be- highly focused, keeping the flight develop- tween management lines as a potentially signif- ments on track technically and financially. icant issue for the Mars program going for- Second, the current Mars Exploration Program ward. Director has left that position for a new position in the office of the Associate Administrator for Recommendation 4. Strategy and Plans as NASA’s Senior Advisor To the extent possible, missions and in- for Agency Architectures and Mission Align- struments should be openly competed; ment, where he “will lead an update of the where specific investigations are desired, ob- Agency’s Mars exploration planning, including jectives can be defined and then opened to further development of our investment strategy competition. and partnership opportunities… Overall, he

42 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations Rationale: The value of competing both in- V.B MASWG Recommendations for struments and missions has been demonstrated a Successful Future Mars numerous times, in terms of both the robustness Exploration Program and cost of development, and the quality and In addition to the high-level recommenda- value of the science that is returned. There are tions made in the previous subsection, we pre- multiple approaches to competing missions. sent 10 specific and detailed recommendations Mission concepts and the science to be ad- that we believe will help to ensure the success dressed can be competed fully, as was done of the revamped Mars program. These gener- with the Mars Scout Program and is being done ally follow from and elaborate on the high- in the today. Science ob- level recommendations discussed previously: jectives can be defined up front, with competi- tion for implementation, teams, and instru- ments, as is done today with the New Frontiers Recommendation 6. Program. Or competition can be carried out for The guiding principles required to drive integrated science payloads to sit on a space- the program forward should include the fol- craft provided by NASA direction and man- lowing: aged by a NASA center, as was done with the • Be responsive to scientific discoveries by Mars Exploration Rovers. Where mission sci- ongoing and new missions. ence or programmatic objectives are defined up • Address science priorities as defined by front, open competition to provide instruments the Decadal Survey and by MEPAG. or science investigations should be carried out. • Have missions build on each other both scientifically and technologically. Recommendation 5. • Compete missions or payload elements to A robust Mars Exploration Program will the extent possible within strategic direc- require affordable access to multiple places tion. on the Martian surface and affordable long- lived orbiters. NASA should invest early to • Inject a sufficient number of flight oppor- expedite the rapidly evolving small space- tunities to sustain technical capability craft technologies and procedures to achieve and to achieve steady progress on key these capabilities at lower costs than past goals; frequent missions may be essential missions. to attracting the commercial sector and international partners. Rationale: The Mars program cannot be robust in investigating the highest scientific • The choice of mission class should be de- priorities unless lower-cost approaches can be termined by the specific science objec- developed for long-lived orbiters; small space- tives. craft; and EDL for landers and rovers. Capa- Rationale: These are straightforward prin- bilities in these areas are evolving rapidly at ciples that will help ensure that the Mars pro- present, especially for small spacecraft, but an gram is integrated into a single coherent pro- investment from NASA will be required to en- gram. sure that these capabilities can be utilized in a timely manner for Mars missions.

43 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations Recommendation 7. Recommendation 9. The program should be sustained at a The program should have a protected, steady funding level, with commensurate re- adequately funded, and competed technol- sults. The size and scope of the program— ogy development program to advance in- and, therefore, the progress that it can strumentation and developments in key ar- make—will depend on the resources pro- eas (e.g., as has been done for the MAV). vided. The technology invested should be focused Rationale: Having a steady funding level and leveraged within NASA and with other will ensure that mission planning and imple- agency and commercial entities. mentation can proceed without the inefficien- Rationale: As our understanding of Mars cies that inherently result from uncertain fund- advances, we recognize a need for new meas- ing and replanning associated with changing urements and for different capabilities of plat- funding. Options for the size of the program forms. These require advance development are given in Section VI; clearly, the scientific through a separately funded program in order results that can be obtained and the rate at to ensure that capabilities are available when which they are achieved will depend on the they are needed. It is always tempting to re- funding level. duce or eliminate funding for such technology- development programs when budgets get Recommendation 8. squeezed; this puts future programs at risk, so Utilize PI-led small spacecraft and Dis- a protected program is necessary. We recog- covery-class and New-Frontiers-class mis- nize, in addition, that many of the desired capa- sions, competed in a separate Mars Explora- bilities are not unique to Mars planning nor tion Program line while addressing strategic even other targets of NASA’s planetary pro- goals. gram; some development might be carried out Rationale: There are two points here. First elsewhere either within NASA or through com- is that for a Mars Exploration Program to be vi- mercial entities. able, it must develop science missions for flight; this is the way NASA makes scientific Recommendation 10. progress. Second is that it will be most produc- With regard to technology development, tive for the program as a whole if the overall a critical need for Mars exploration is that funding can support a range of mission sizes NASA develop low-cost approaches for en- ranging from small spacecraft up through New try at all size classes, including en- Frontiers-class missions to be integrated into a try, descent, and landing. viable program architecture. This means hav- Rationale: Continued exploration of Mars ing the flexibility to accommodate missions will require access to the surface by multiple with different development timelines and fund- lander or rover vehicles. At present costs, mul- ing profiles. Note that we refer to Discovery tiple entry vehicles of MER or PHX size class and New Frontiers here only to provide a com- would be prohibitive, and there are no existing parison point that will indicate the anticipated entry vehicles for the smaller spacecraft that size/cost of missions. We are not suggesting still could carry out significant surface science. that these Mars missions compete within those It is imperative for future Mars exploration that specific programs; in fact, we are suggesting lower cost vehicles capable of delivering exactly the opposite: that missions in these dif- spacecraft that have substantial capability to ferent classes be part of a single, separate Mars the surface be developed. Entry vehicles from Exploration Program. small spacecraft up through at least MER class are necessary.

44 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations Recommendation 11. Rationale: Numerous examples exist in NASA should develop low-cost ap- which international collaboration has allowed proaches for long-lived orbiting small space- significant science to be carried out success- craft and for aerial vehicles, landers, and fully (see Section IV.C). At the same time, rovers to provide access and mobility after there are counterexamples showing the diffi- landing. culties that can arise. TGO is an example, in Rationale: Lower cost approaches to long- which NASA backed out of participation rela- lived spacecraft have not been developed but tively late in the process (after selection of sci- are necessary for affordable Mars exploration ence instruments). In engaging in international and to take advantage of rapid technology evo- collaboration, it is necessary that: 1) NASA in- lution in this area. Consideration of making volve the respective scientific communities in some of these craft long-lived does not mean the definition and execution of joint missions; imposing Flagship-class redundancy on such 2) to the extent possible, missions and instru- missions but rather developing low-cost ap- ments should be competed openly in order to proaches to risk mitigation, including through get the best science; and 3) NASA-supported simulation, appropriate levels of testing, and mission participants on non-NASA missions possibly multiple craft. (Instrument Teams, Science Team members, Participating Scientists, Interdisciplinary Sci- Recommendation 12. entists) should be supported financially at ade- quate and appropriate levels to achieve the mis- NASA and the Mars community should sion objectives. study the feasibility of adapting the CLPS program to Mars. Recommendation 14. Rationale: A successful Mars-focused Adequately fund the analysis of returned Commercial Mars Payload Services (CoMPS) mission data so results can be achieved in a could serve as a programmatic vehicle to allow, timely fashion; support extended missions as at reduced cost, development of technologies for future exploration, as well as delivery of long as they make solid scientific progress. specific science payloads. We recognize the is- Rationale: Data that are not analyzed are sues here, in that 1) the CLPS program at the data that may be lost to the scientific enterprise. Moon, though promising, has not yet been Extended missions with their increased cover- demonstrated as successful; 2) Mars provides age in space and time have added to the infor- different challenges due to its distance and at- mation available for analysis and the opportu- mosphere, and 3) there would have to be nities for interdisciplinary study. Organization enough potential flight opportunities to justify into new data products brings fresh insight to the necessary up-front investment from com- addressing fundamental questions about Mars mercial entities. Thus, the recommendation and provides valuable feedback to the observa- here is to study the feasibility of implementing tional planning still in progress. Analysis of such a program. multiple data sets brings new understanding and more realistic testing of hypotheses and of Recommendation 13. model simulations. This takes effort, both in the analysis of data and the resulting formula- NASA and the Mars community should tion and testing of new hypotheses. Even with continue to explore, negotiate, and support major advances in the handling of large data international collaborations as a means of sets and in the tools for their analysis, funded leveraging flight opportunities to achieve researchers are the means by which the ad- compelling science. vances are made.

45 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations Spacecraft missions are perpetually at risk Note that this is not a blanket push for all for having their budgets cut, and this tends to extended missions under all circumstances. impact the science activities most severely. Properly designed and implemented Senior Re- Some Mars missions have had their budgets cut views would serve as a check. even during their primary mission. Others have been funded in extended missions at a level that Recommendation 15. only allows data to be collected and archived Enhance interactions between the revi- but not analyzed. This throws the analysis bur- talized Mars Exploration Program and the den onto the Research and Analysis (R&A) Human Exploration and Operations Mis- programs and decreases the likelihood of posi- sion Directorate (HEOMD) to define needs tive feedback on the data acquisition process. It and the opportunities to address them. also limits the involvement of the very experi- Rationale: Given that one of NASA’s ment teams that best know their instruments long-term goals is to carry out human missions and the potential of the data they produce. It to Mars, it is necessary to have appropriate in- is imperative that adequate funds be provided teractions and engagement between the human to ensure the reduction and analysis of space- program and the Mars Exploration Program. craft data in a timely manner. Deferment of Creating a formal group to oversee interactions analysis can lead to loss of science opportuni- would ensure that 1) adequate, accurate, and ties (for transient phenomena) or loss of per- appropriate Mars knowledge and experience sonnel capable of carrying out data reduction are provided in support of human missions, and and analysis (through retirements or transfers 2) scientific progress will be sustained and ad- to other projects). That leads to fewer opportu- vanced by missions with humans when they do nities for new researchers to bring fresh per- fly. Robotic missions have lead times of 4–7 spectives to bear and for them to gain valuable years, and follow-up to new discoveries must flight experience. For all of these reasons, mis- accommodate the 26-month cycle of the most sions should continue to be extended after their fuel-efficient launches from Earth to Mars. primary missions and funded at adequate levels Human missions are being planned to fly some- as long as they are doing valuable science or time in the 2030s; thus, interactions need to serving valuable programmatic functions; begin now, and missions that can support both funding for extended missions must be built the scientific and programmatic objectives into budgetary planning. need to appear in long-term planning now.

46 Mars, the Nearest Habitable World October 2020 MASWG V. Recommendations

Recurring Slope Lineae (RSL) in eastern : Mars Reconnaissance Orbiter (MRO) has observed these dark narrow streaks appear and lengthen down steep slopes during warm , only to fade as surface decline seasonally. The RSL then recur in subsequent Mars years. Their nature has been much debated, with latest discussion favoring dry flows. (Credit: HiRISE / U. Arizona / JPL / NASA)

47 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035

VI. A Mars Program Architecture for 2020–2035

Mars exploration has long marched to the At the same time, and despite the successful paradigm of global reconnaissance, in situ missions to Mars by many nations, there re- analysis, and sample return originally articu- main unexplored terrains (e.g., in situ on the lated in An Exobiological Strategy for Mars polar ice caps and in the subsurface), the chal- Exploration (NASA, 1995). Orbiters have lenge of investigating the amazing diversity of searched for sites of particular interest (such as the surface environments recorded over the those with evidence for having had liquid wa- long history of Mars, and major outstanding ter) and have put them into the global context questions about the history of Mars. The cov- of the evolution of Mars. Landers and rovers erage in space and time of even the modern en- have examined specific sites in situ to test the vironment is incomplete at the level of detail understanding obtained from orbit, to explore needed to address these questions. in detail the physical and chemical evidence Here, we describe the missions that can that is present at small physical scales, and to take us, as an integrated program addressing evaluate the potential ancient habitability of the the full range of Mars science, to the next level sites by microbes. And, the MSR campaign, of understanding of Mars as a planet. We pro- initiated with the launch of Perseverance, is the vide multiple options for “mission arcs” that culmination of this effort so that carefully se- could address different areas of science within lected materials can be returned to Earth for an affordable program, while utilizing the full study by the full range of Earth-science labora- range of mission classes. tory capabilities. Collectively, these ap- proaches address all aspects of Mars science.

Left: Missions currently operating on Mars or in Mars Orbit. Right: Mars Missions launched in 2020, currently in development or conceptual design. (Credit: NASA)

48 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 VI.A Mission Classes for Mars open the way for commercial participation in Exploration providing needed services, particularly in the areas of how to get the instruments there and To realize the scientific potential for under- how to get the information back. standing Mars, a Mars Exploration Program is needed to define a range of related science ob- The cost, requirements, and performance jectives; to invest and leverage technical devel- relationships for small spacecraft focused on opments in spacecraft, propulsion, and commu- science have not yet been demonstrated in deep nications systems and scientific instrumenta- space or at Mars. The first round of planetary tion; and to define risk approaches and devel- SIMPLEx missions is still in development, and opment strategies that can achieve the needed other concepts generally have not yet flown. reductions in mass and power while providing One small-spacecraft mission that is in process required capabilities, all at an affordable cost. is the EMM Hope, currently in to Mars and scheduled to arrive in early 2021. At the A salient principle is to break the science cost for Phases A–D recently released publicly questions into discrete objectives and then to by the project manager, EMM falls within the match them with an appropriate mission size or range considered here for small-spacecraft mis- cost class. The current metric for flight mis- sions. Orbiting small spacecraft seem within sions has been Discovery-class (development reach, but the ability of class D or single-string costs capped at $500M, not including launch missions to observe over multiple Mars years is vehicle), New Frontiers-class (similar cap of uncertain. Another critical need is to have mis- $1B), and Flagship missions (> $1B). An ex- sions in this class that can land on Mars with citing new development is the growing capabil- sufficiently capable payloads. PP and contam- ities of small spacecraft (Section IV.B). ination issues will have to be addressed (see The term “small spacecraft” encompasses a Appendix B). wide range of concepts and can be defined in Many science objectives will need to be ad- terms of mass, cost, or even deployment ap- dressed by the more capable Discovery- and proach (e.g., rideshare). In this report, the em- New Frontiers-class missions. As discussed phasis is on the ability to achieve high-priority earlier, a Mars Exploration Program should science at lower cost, a combination that can strive to make best use of all mission classes vary widely depending on the science objec- by: tives and observation requirements. The ongoing rapid development of small- • Choosing missions in the appropriate size spacecraft capabilities has the potential to rev- class while integrating them into coherent olutionize Moon and Mars exploration by program lines that can achieve major sci- providing more affordable and more frequent ence objectives; flight of payloads for scientific exploration and • Set the requirements early and realistically for meeting human exploration needs. Exten- on spacecraft size, capability, and longevity; sive use of small spacecraft as part of a Mars • Match the level of oversight to the mission Exploration Program is particularly appealing complexity and the skill and experience of during an otherwise MSR-focused decade be- the team and partners; cause such use could facilitate a complemen- • Develop and/or leverage key technical capa- tary Mars Exploration Program that achieves bilities (e.g., smaller landers, long-lived high-priority science with frequent launches at small orbiters, scientific instrumentation); an affordable program cost, thereby making and substantial progress on key science questions • Assist the process for transit to Mars, in- and filling strategic knowledge gaps for mis- cluding early identification of rideshare sions with humans. That frequency may also

49 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 opportunities, and maintain the communica- flight elements of the MSR campaign are pro- tions infrastructure needed to support data jected to be in their development phases. return, as these can be drivers to mission The increased capabilities called out later in class. the mission arcs are typically driven by the sci- entific objectives and the payload, as more VI.B Program Architecture: complex measurements are needed to follow up Perspectives and Possibilities— earlier discoveries or to achieve more challeng- Mission Arcs ing science objectives (e.g., polar cap drilling). To demonstrate how a Mars Exploration The proposed mission arcs here include both Program could pursue compelling science ob- Discovery-class and New Frontiers-class mis- jectives while utilizing a suite of missions, we sions to meet the more challenging objectives, have defined four “mission arcs” or mission- and the program must have funding sufficient sequence scenarios; these are examples and do to utilize them if it is to succeed. not encompass the entire range of compelling While individual missions could be com- options. Other mission arcs are certainly pos- peted through the small spacecraft or Discov- sible, and the number and scale of arcs that can ery or New Frontiers processes, inclusion in an be pursued in parallel obviously depend on the adequately funded strategic program line available budget. A prime function of an ongo- would ensure a consistent approach with mis- ing Mars Exploration Program would be to sions building on one another (Section IV.A). work with the science community to define Note that while a mission arc typically fo- mission arcs actually to be implemented and to cuses on a single theme or high-level objective, work issues of budget and schedule, including a single mission may contribute to more than working with international and/or commercial one arc, and pursuing more than one arc in a partners. The point of the exercise here is to timely fashion can enhance the return of both. demonstrate that, although much still needs to That reflects the interdependency of processes be done technically and programmatically, im- in real environments and the value of contem- portant science can be achieved. Clearly, how- poraneous and/or complementary measure- ever, the pace of progress will depend on the ments. funding level. In Tables VI-1 through VI-4, as in Figure Tables VI-1 through VI-4 describe the four III-1, and in the discussion below, the mission mission arcs presented here as proofs of con- classes are defined by: cept. Each example identifies an area of com- • SSc denotes Small Spacecraft class. pelling science, with a brief statement of goals The life-cycle costs (including launch and then a progression or choice of missions vehicle and Phase E ops/science) are taken that would be strategically linked to achieve to be in the range of $100M–300M in FY20 those goals. While there are many possibilities, dollars (Sections III and VI.A). There was the ones cited here are meant to demonstrate considerable debate about this cost range. that such strategically linked, compelling arcs The SIMPLEx cost cap was viewed by can be defined. Often, there is a three-phase many as being too restrictive to achieve progression from utilizing smaller missions to compelling science in multiple missions build on what is known today (e.g., diverse en- across the mission arcs. That cap is ~$55M vironments) to larger missions that would without launch costs, which are included achieve ground-breaking progress. An effort is here. While one could argue that $300M is made to utilize lower-cost spacecraft early in really a low-cost Discovery-class mission, the mission arc during a period when the next those missions would be competing against grander missions. Here, we a

50 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035

mission that is matched to a particular scien- • DSc and NFc describe missions having ob- tific focus within an integrated sequence of jectives and requiring resources similar to missions. Costs may drop as technology ad- the Discovery and New Frontiers classes, re- vances, but there are challenges of landing spectively (Section VI.A). and functioning in extreme environments • FLG describes a Flagship-class mission. that still need to be met. Based on current We expect that missions at this scale would trends, some small spacecraft missions not be affordable until after the currently could be closer to the lower bound, which conceived MSR suite of missions has re- would provide more opportunities when a turned its samples to Earth, but advanced program budget line is fixed. planning could proceed.

Table VI-1. Mission Arc #1: Diverse Ancient Table VI-2. Mission Arc #2: Subsurface Structure, Environments & Habitability Composition & Possible Life Explore diversity of ancient Mars, following The subsurface of Mars is largely unex- up on the thousands of possible sites, to un- plored, and yet its structure and composition Compelling Compelling derstand early planetary evolution and the Science hold many clues to the early evolution of Science nature, timing, and geochemistry of environ- Mars. Further, it could be the refuge of an ments, habitability, and/or biological poten- early Martian . tial of Mars. Explore the subsurface of Mars for water, Goals Quantify relative timing of major climatic / chemical gradients, and signs of extant life. Goals geologic / biochemical events and transi- tions in order to understand planetary evolu- • Phase 1: Orbiter missions to 1) improve tion and biotic / prebiotic change. surface and gravity maps and 2) map ice structures and geomorphology beneath dust-covered terrains. • Phase 1: High-spatial resolution mineral- – SSC: Low-altitude magnetic survey and ogy (≤ 6 m/pixel) from orbit to find best gravity mapping. sites. – DSc/NFc: Orbiter with surface / subsur- – SSc: Mineral mapping by orbital spec- face radar imager and sounder. Syner- troscopy. gistic with ice science Arc #3. – DSc: Spectral and visual imaging from • Phase 2: Land electromagnetic sounders orbit. Synergistic with Arc #3. and active-source seismic devices at key surface locations from which to remotely • Phase 2: Surface exploration of a subset probe subsurface structure, conductivity, of these environments with small landers. and geochemical gradients. – SSc: Investigation of multiple sites us- – SSc/DSc: Dedicated to landed remote ing pinpoint landing, mobility (air, Mission Arc EM sounding and active-source seismic ground). devices; trace gas fluxes. Mission Arc – Tech enabler: Affordable access to – Tech enabler: Affordable access to dozens of sites in the SSc. multiple sites. • Phase 3: At most promising sites, drill / in- • Phase 3: In-depth characterization of the vestigate to great depths, with in situ bio- most promising sites in terms of geochem- geochemical analysis. istry, mineralogy, and biosignatures. – NFc/FLG: Probe deeper at the most – NFc: Detailed in situ imaging and spec- promising sites revealed in Phase 2. troscopy, biogeochemical sampling and – Tech enabler: More advanced instru- analysis, and age dating. mentation, active devices, and drilling nd – FLG: Life/ analysis; 2 techniques. Access to subsurface MSR? portals (e.g., caves, vents, cliffs). – NFc: Prove out potential resources for in situ resource utilization (ISRU) by hu- mans.

51 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035

Table VI-3. Mission Arc #3: Ice—Geologically Table VI-4. Mission Arc #4: Atmospheric Recent Climate Change Processes and Climate Variability Understand Martian ice ages in terms of the Record variability of the current climate from distribution and stratification of ice as it was Compelling hours to decades and the processes of emplaced / removed over the last hundred Compelling transport and photochemistry, Sun-Mars in- Science Science million years, both in the polar regions and teractions, exchange of water, dust, CO in lower latitudes. 2 and trace gases. Climate Change: Exploit the detailed record preserved in ice deposits, understand pro- Climate: Understand processes of climate cesses, and quantify relation to orbital cy- evolution, including validation and improve- Goals cles. : Seek evidence of past ment of models used to understand climate or extant life preserved in ice. Resources: Goals change over time. Strategic Knowledge: Are there deposits suitable for supporting Provide environmental data for design and human activities on Mars? implementation of robotic and human mis- sions. • Phase 1: Determine extent and stratifica- tion of near-surface ice across the planet • Phase 1: Climate Variability & Strategic from orbit. Knowledge – SSc: Polar energy balance mission. – SSc: Multiple, long-lived SSc to achieve – DSc: Synthetic aperture radar and radar global and local time coverage (e.g., sounding. Synergistic with subsurface areostationary), and long-term records Mission Arcs #1–2. OR of temperature/pressure, , and aer- – NFc: Combine radar and high-resolu- osols and water (columns and profiles). tion imaging, potentially with Tech enabler: Long-lived small spectrometers for ice discrimination and spacecraft. thermal inertia (depth to ice); aids char- – DSc: Multiple measurements on one acterization of diverse sites (Arc #1) and spacecraft, including active sensors exploration of subsurface (Arc #2). (e.g., for winds, aerosols). Support for SSc constellation. Mission Arc • Phase 2: Quantify drivers of ice emplace- Mission Arc • Phase 2: Improve understanding of cli- ment / removal. mate processes (non-polar ice); comple- – DSc: Landed imaging, shallow drilling / ment ice landed missions (Arc #3). trenching, meteorology on polar cap – DSc: Intensive 1–2 non-polar field cam- and/or layered terrains. Complementary paigns to understand onset, to low-latitude process field work (#4). and momentum exchange, and trace gas transfer. • Phase 3: Observe and analyze detailed • Phase 3: Understand boundary layer/sur- ice stratigraphy. face exchange – NFc/FLG: Landed imaging, deeper drill- – NFc: Network of landed stations to pro- ing, and meteorology on polar cap ice file boundary layer fields and measure even in the polar night. near-surface fluxes across Mars. (Measurements should be simultaneous with fields measured by small satellites.)

2 billion years. CRISM and OMEGA data VI.B.1 Mission Arc #1: Diverse Ancient combined with constraints on stratigraphy from Environments and Habitability HiRISE indicate nearly a dozen distinct, habit- A major and compelling result of the MEX able aqueous environments (e.g., Murchie et al. and MRO missions is the discovery of wide- [2009], and many subsequent studies). Based spread and ubiquitous alteration of ancient No- on stratigraphy and crater , these trace achian crust (Ehlmann & Edwards, 2014). the climatic evolution of early Mars. Yet, the Early stratigraphic sequences comprise a rich nature, duration, and drivers of major environ- and diverse record of aqueous environmental mental transitions are still unclear, as is how conditions that largely ceased after the first 1– these transitions may have affected the

52 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 habitability of surface and subsurface environ- To address these goals, Phase 1 in this mis- ments and whether these environments were sion arc is to improve on orbital mineral map- ever actually inhabited. ping of environmental transitions. This can Unlocking the geologic sequence stratigra- readily be accomplished using an SSc orbiter phy of these transitions through time is crucial with instruments that are in development for to interpreting the history of this dynamic and future launch opportunities (e.g., imaging spec- changing period on early Mars, as well as un- trometers or multispectral imagers similar to derstanding how early solar, impact, and inte- Polar Radiant Energy in the Far Exper- rior processes drive the evolution of habitable iment (PREFIRE) for Earth Ventures or Lunar rocky planets generally (Ehlmann et al., 2016). /HVM3 for SIMPLEx). Within a This requires detailed investigation of many di- DSc mission, additional instruments such as verse environments. even higher resolution imagery or improved To date, instrumented rovers have visited spectral fidelity in the long-wave infrared could only four locations, with three or more to be be included. This phase and its instrumentation added in the next several years if successful. would have synergies with mission Arc #3, These locations represent only a small fraction where spectral instruments are used to map sur- of the thousands of possible sites that have been face ice composition or determine ground ther- identified from orbit that can help define early mal inertia. planetary evolution, and the nature, timing, and Phase 2 would be the true game changer, as geochemistry of environments, habitability, it would require affordable access to multiple and biological potential of Mars. Thus, more sites on the ground in order to explore the true needs to be done from orbit, together with in diversity reflected in the enhanced orbital data situ investigations at multiple, carefully chosen (Ehlmann et al., 2016). As mission costs have sites. crept upward, access to the Martian surface is Extended coverage at better spatial resolu- currently barely affordable in New Frontiers tion is key to understanding the record retained for mobile systems, and even fixed landers in these early aqueous environments, via the need significant reuse of hardware or interna- distribution and abundance of alteration phases tional contributions to fit within Discovery. as well as their geologic implications. Current This second phase requires technology de- spatial resolution and coverage at the near-in- velopment that leads to affordable surface ac- frared of greatest interest are from cess with mobility, either by rovers or aerial OMEGA and CRISM (globally at platforms (Finding 7 in Section III and Recom- ≥ 200 m/pixel) and from CRISM (~ 18 m/pixel, mendation 5 in Section V). Multiple small plat- but only for a carefully targeted ~2% of the forms, perhaps delivered and supported by a planet). single “,” may be essential to make The improvements in spatial and spectral further progress in landed science. resolution and capability in going from the Having characterized numerous sites span- MGS Thermal Emission Spectrometer (TES) ning a range of geochemical settings, Phase 3 to the Mars Odyssey Thermal Emission Imag- would follow up with additional detailed anal- ing System (THEMIS), from MEX OMEGA to ysis in situ or deep drilling at the most promis- MRO CRISM, and from the Viking Orbiter ing site. In situ isotopic analyses and age da- cameras to the MGS Mars Orbiter Narrow-An- ting could further revolutionize our under- gle Camera (MOC) to MRO HiRISE, all have standing of the geologic timeline and staging of illustrated that such improvements lead to ma- events that are currently only constrained by jor new discoveries. and qualitative measures for visual weathering and erosion. Current

53 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 studies suggest these may require larger landed unexplored, with inferences of subsurface platforms that are presently NFc class or even structure and architecture from orbital radar larger. imagery, visual topography, and gravity We can also envision a potential second providing the most data. Only one mission, In- MSR in the mid-2030s, where the samples Sight, has been fully dedicated to exploring the from the new site would broaden what was interior seismicity and heat flow. While In- learned from samples collected in the current Sight will open up analyses to this third dimen- MSR campaign, would investigate additional sion, challenges to the progress of its thermal environments for biosignatures based on new probe and to the analysis of data from a single in situ analyses, and/or characterize / certify the seismic station will limit what can be learned. best site for future in situ exploration by astro- To go beyond global-scale geophysics will nauts on the ground. require different instrumentation. While the detection of extant subsurface life has its chal- VI.B.2 Mission Arc #2: Subsurface lenges, a place to start is to determine where Habitability and Possible Life water may be present and where there are bio- Better orbital data and innovative rover ob- logically relevant energy sources. servations at the surface have established the The goal of this arc is to “follow the water” past existence of dynamic and long-lived sub- at depth, along with trace gas fluxes from the surface aqueous systems on early Mars. There subsurface. The three-phase approach to this also is the tantalizing suggestion that liquid arc would be: 1) regional to global surveys (briny) water may exist 1.5 km below the ice from orbit, 2) distributed reconnaissance cap near the southern pole of Mars (Orosei et landers (likely with EM sounders), and 3) ro- al., 2018), raising the possibility that subsur- bust, deep drilling to different depths. face liquid water exists today, albeit at depth, Phase 1 of this mission arc consists of or- and that more ice deposits could be detected biter missions to improve maps of surface mag- with advances in sensing technology. netism and gravity and to obtain maps of ice The structure, architecture, and composi- structures and geomorphology beneath dust- tion of the Martian crust hold many clues to the covered terrains. Our best knowledge of the early evolution of Mars, and its volatile reser- magnetic field is limited to voirs record geologically young climatic varia- measurements taken on low-altitude passes of tions. In addition to achieving major scientific the Mars Global through the upper at- advances, this effort would gather fundamental mosphere during its orbit insertion and aero- information for future ISRU. braking phase, complemented by spatially lim- Lastly, telescopic, orbital, and rover obser- ited resolution data from MAVEN. vations have pointed to the possibility of the re- Gravity, currently derived from spacecraft lease of methane gas on a range of spatial and tracking using their communications systems, temporal scales. The origin and nature of such would benefit dramatically from a Gravity Re- exhalations is a prime target for subsurface ex- covery and Interior Laboratory (GRAIL)-like ploration. If life ever got started on Mars, the mission, especially if sensitivity to deep water subsurface could be the present-day refuge of could be achieved. Mapping near-surface ice an earlier Martian biosphere. The possibility of deposits, another essential step, can be accom- detecting extant life in the Martian subsurface plished with a DSc or NFc class orbiter with is a major driver of this arc. imaging and sounding radar as well as comple- Apart from radar soundings of the polar mentary visible imaging. Such a mission caps and limited areas of the mid-latitudes, the would be entirely synergistic with Mission Arc subsurface of Mars is almost completely #3 for Ice Science.

54 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 In Phase 2, reconnaissance from Phase 1, and longer-term obliquity variations (e.g., integrated with past measurements, would Smith et al. [2020]). identify key surface locations with promising Thus, this mission arc is focused on recent characteristics for probing subsurface struc- climate change as recorded in surface and sub- ture, conductivity, and geochemical gradients. surface ice deposits. It seeks to understand As we have only very limited knowledge of Martian ice ages in terms of the distribution and how orbital data translates to subsurface char- stratification of ice as it was emplaced and re- acteristics, strategic analyses of several prom- moved over the last hundred million years, both ising sites are required in order to build exper- in the polar regions and in lower latitudes. tise and knowledge to follow up with larger ef- Understanding the climate record retained forts. This phase can be accomplished with in ground-ice reservoirs requires better obser- SSc and/or DSc missions dedicated to landed vational constraints on the lateral extent and remote electromagnetic sounding, ground-pen- volume of ice, as well as the depth to the top of etrating radar, and active-source seismic de- the ice table at low latitudes where ice is ex- vices best done at multiple sites. pected to be buried under several meters of dry If orbital sensitivity to deep water or brines overburden. The recent detection of massive is not forthcoming, it may be best to focus from ice there, rather than simply pore-filling ice, the start on technology development of small challenges current thermal models that predict landers that could be deployed at several sites any near-surface ice should be geologically to measure trace-gas fluxes and to use EM young and actively retreating in the current cli- sounding to identify local subsurface water. To mate (Bramson et al., 2017). investigate the biological potential of shallow In the polar regions, while coarse internal ice, a more sophisticated DSc lander might be stratigraphy is observed in radar sounding data chosen in this phase. of the PLD, the scale of layers seen in MOC, From Phases 1 and 2, promising options HiRISE and Context Camera (CTX) imagery is will be identified for the most ambitious and much finer, and the link between radar layering costly phase of the arc. In Phase 3, the objec- and imagery layering remains unclear. Major tives are to investigate to great depths, possibly unknowns regarding the climate history rec- via drilling with in situ biogeochemical analy- orded in the PLD include the time span rec- sis. This may require a larger mission class, orded in the PLD (possibly different between NFc or FLG, to probe deeply with advanced north and south by an order of magnitude or drilling techniques and instrumentation for more), the completeness of the record, and the chemical and gas analysis. temporal resolution in individual layers. To take the next step, we need to under- VI.B.3 Mission Arc #3: Ice Mapping and stand the processes that form and remove ice Geologically Recent Climate strata in the mid-latitudes and the poles, as well Change as to quantify the relationship between that A major discovery of recent Mars missions stratigraphy and the history of obliquity cycles is the prevalence of near-surface ground ice, as (MEPAG ICE-SAG Final Report, 2019). seen, for example, in MRO SHARAD radar re- To address these goals, Phase 1 exploration turns (e.g., Bramson et al. [2015]), HiRISE im- in this mission arc is to determine the extent ages of steep cliff faces exposing thick layers and stratification of near-surface ice across the of dense ice (Dundas et al., 2018), and ice ex- planet from orbit. Depending on funding avail- posed by new impact craters (Dundas et al., ability, this phase could begin with a small or- 2014). In addition, stratigraphy in the polar lay- biter (SSc) dedicated to observing the current ered deposits (PLD) has been linked to recent polar energy balance as a means to determine

55 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 whether and where net annual deposition or net spectroscopy to map water-ice composition of erosion is occurring in the PLD. This would be the PLD exposures at higher resolution than followed by orbital radar imaging and sounding CRISM. These spectrometers also could map at higher frequencies than the current sounders, surface mineral compositions, a major goal of MEX MARSIS and MRO SHARAD. The mission Arc #1. goals of this investigation can realistically be Phase 2 is intended to quantify drivers of accomplished in a DSc mission that also would ice emplacement and removal. This involves have synergies with subsurface science goals in landed science to measure the fluxes of water, mission Arcs #1 and #2. In addition, this phase carbon dioxide, and dust as well as the seasonal can address whether there are near-surface ice and annual processes resulting in layer for- deposits suitable for supporting future human mation at the poles or transport into and out of activities. An enhanced New Frontiers class the mid-latitude regolith. Measurements would NFc mission would add thermal-infrared ob- include comprehensive meteorology that has servations to determine surface thermal inertia synergies with Mission Arc #4, or shallow related to the depth to the shallowest (< 1 m drilling or trenching in order to measure the deep) ground ice and short-wave infrared

HiRISE view of water-ice (blue in the above color-stretched image) exposed in a cliff in high southern latitudes (NASA Credit: MRO / HiRISE / U. Arizona / USGS / JPL / NASA)

56 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 fine-scale vertical structure in polar or mid-lat- VI.B.4 Mission Arc #4: Atmospheric itude ice. Processes and Climate Variability Of particular interest is the measurement of The last 20 years have seen significant ad- isotopic ratios, especially D/H, which is known vances in our knowledge of the Martian atmos- to vary seasonally in both the lower and upper phere and climate system. However, funda- atmosphere (e.g., Villanueva et al. [2015], mental gaps in our understanding remain that Clarke et al. [2019]). The relationship of its at- require additional observations to resolve. mospheric signature to polar and mid-latitude This mission arc seeks to better character- ice reservoirs would provide compelling links ize the controlling processes and the state of the between the ice stratigraphy and past climate present-day Martian climate in response to epochs (Jakosky, review in press). It is notable modern drivers. An understanding of these that, of the early failures of , processes can then be used to extrapolate into Mars Climate Orbiter, and Mars Polar Lander, the past when driving conditions and atmos- only from the last—a small mission to land on pheric composition may have been different. and trench into polar layered terrain—has the A test of that understanding is the ability to science not been recovered by subsequent mis- simulate the modern climate and its variability sions. This arc would fill that void. over a range of timescales, from hours to dec- Phase 3 of this arc builds on preceding anal- ades or longer. In that way, a knowledge of the yses with orbital observations and landed as- basic transport processes associated with aero- sessment of the detailed ice stratigraphy. This sols, volatiles, and trace gases provides a large-scale NFc or FLG mission would involve means for understanding Mars’ climate landed observation of ice stratigraphy, deeper throughout its history. Such an emphasis drilling than in the prior phase, and perhaps me- would also naturally include the basic seasonal teorology on the polar-cap ice throughout the cycles of dust, CO2, and H2O, but also photo- full annual cycle (including the frigid polar chemistry, atmospheric boundary layer ex- night) to characterize the deposition and ero- changes with the surface, Sun-Mars interac- sion of the seasonal CO2 ice layer. Such a mis- tions, and the validation and improvement of sion could truly revolutionize our understand- models used to investigate climate change over ing of the Martian climate system and habita- time. bility. Although measurements of atmospheric Water is the key to habitability on Mars, aerosols, temperature, and column water vapor and as such, ice reservoirs are an important po- have been made for several Mars years tential preserver of either extant or extinct life. (Haberle et al., 2017), atmospheric studies have Microbial life is known to exist in a wide range lacked the necessary combination of coverage, of frozen terrestrial habitats (Boetius et al., temporal, and spatial scaling needed to more 2015), so ice reservoirs are one possible refugia systematically address transport processes and if life ever got started on Mars. Broader goals climate variability. Winds and water vapor for the Mars program related to ancient habita- vertical distributions have not been measured bility and subsurface exploration (Mission extensively, and profiling of near-surface fields Arcs #1 and #2) are synergistic with the deep and exchanges with the surface are woefully ice drilling and subsurface exploration that is lacking. A compelling set of missions could the end phase of this mission arc. Technologies acquire the data needed to investigate the main to achieve this would have application to other scientific questions. icy worlds.

57 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 As with other mission arcs presented here, areostationary orbit) with current instrumenta- the collection of missions needed to make pro- tion. (The just-launched EMM Hope mission gress is organized into three phases, with the may be a start to this.) The observation goal full mission arc intended to address the follow- would be long-term global records of tempera- ing program elements: ture/pressure, winds, and both column and ver- • Orbit-based characterization of atmospheric tical profiles of aerosols and water vapor. Be- circulation and of transport processes. cause the durability of SSc is not yet proven for the Martian environment, these missions would • Transport of aerosols and their relationship to atmospheric spatial/temporal scales and benefit from a program aimed at achieving long to climate. life for small orbiters. These capabilities could be augmented with a DSc orbiter carrying an • (In-situ) surface-atmosphere boundary layer integrated payload including new remote sen- interactions (e.g., water vapor and other sors, e.g., active systems, such as lidar for trace gas measurements). winds and aerosols, submillimeter for tempera- • Acquisition of strategic knowledge, in the ture profiles, water vapor profiling, and mid- form of environmental data for design and dle-atmosphere winds even in the presence of implementation of robotic and human mis- aerosols (MEPAG NEX-SAG Report, 2015). sions. In Phase 2, landed missions would investi- In Phase 1, knowledge gaps are addressed gate exchanges of the atmospheric boundary by a set of multiple SSc, or perhaps more effi- layer with the subsurface and the deeper atmos- ciently by a combination with a DSc. Recent phere with either one or two intensive non-po- technical developments should enable small or- lar field campaigns. Emphasis is on the com- biters to provide global spatial and diurnal local plement of instruments needed to understand time coverage (e.g., with some in an the onset of dust storms, the interplay of water

The Mars atmosphere today: A large cyclonic storm is seen near the north , while the aphelion water- ice belt is prominent across the low latitudes (middle of image).

58 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035 vapor and momentum exchange, and trace-gas study but are meant to provide some idea of interactions between the surface and atmos- scope if two or more of the mission arcs were phere. The implementation could be based on to be pursued. a DSc landed platform designed to make the In Table VI-5, the following rough order- proper measurements in situ (including from of-magnitude costs were arbitrarily assigned: unobstructed masts) and through up-looking $200M for SSc, $750M for DSc, $1250M for remote sensing. A key is to operate continu- NFc. Important assumptions include: ously while making high-frequency measure- • The numbers in FY20 $M are meant to be a ments. This phase would be complementary to representative average. No attempt was measurements in Arc #3 at a polar site. made at year-by-year cost profiles and no in- Because of the tightly coupled and nonlin- flation was computed; ear nature of the Mars climate system, the big- • Costs notionally include launch vehicle / gest leap forward in our understanding of cli- rideshare and prime mission Phase E; mate processes will ultimately come from con- ducting multiple observations from landed • The numbers do not reflect possible interna- platforms across the Mars surface simultane- tional contributions or commercial partner- ously with orbital remote sensing, as is done on ships; Earth. • Flagship-class mission launches were as- In Phase 3, the mission arc therefore cul- sumed to occur after 2035; minates with a network of landed stations, with • Costs for missions extended beyond their a funding profile commensurate with a New- prime mission together with instrument and Frontiers-class mission. The collection of plat- spacecraft technology advances could add forms would be tasked with profiling boundary $150M a year or more; and layer quantities (e.g., winds, aerosols, tempera- • No costs needed to complete the MSR cam- tures) and with the measurement of near-sur- paign are included here, including costs to face dynamical fluxes in a variety of terrain analyze, curate, and archive the returned types on Mars. Ideally, the long-term SSc or- samples. bital constellation of Phase 1 would provide the The number of missions to be launched remote sensing needed to characterize the gen- may appear daunting, but reflects the progress eral circulation as it influences the region possible with small spacecraft. The Program is around each of the stations. likely to have to make choices between mission Ultimately, this network could evolve to arcs. MASWG strongly recommends that pro- provide the routine meteorological information gress be implemented on at least two arcs, in- needed to support activities by human explor- terleaving missions as appropriate. Two DSc ers operating on the surface of the planet. It missions in the next 10 years is a reasonable would do so both by providing the environmen- goal, with one or more NFc in the 15-year pe- tal data needed to design shelters, power riod envisioned here. sources and other facilities and by providing As for the large number of SSc, it should be the initial elements of a monitoring network ad- noted that, for both Arcs #1 and #4, many of the visable to support surface operations by hu- small spacecraft are envisioned to have essen- mans in an efficient and safe manner. tially the same payload to be delivered into dif- ferent orbits or at many different landing sites. VI.C Program Scope and Affordability In those cases, several may be developed and Table VI-5 shows the possible number of launched in the same opportunity. missions in each of the proof-of-concept mis- Programmatic coordination of small launch sion arcs. These are not based on any detailed opportunity acquisition or early identification

59 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035

Table VI-5. Mission numbers for the various mission arcs described in Section VI.B and Tables VI.1–4. Costs were roughly estimated assuming (on average) $200M for SSc, $750M for DSc, and $1250M for NFc mission classes. The programmatic support line is specific to these mission arcs; it does not include current R&A, extension of current missions (including Perseverance), or costs associated with handling and analysis of samples returned by the MSR campaign.

and coordination of rideshare opportunities The funding for making major progress with NASA, international, and commercial en- while the MSR campaign is proceeding is com- tities is crucial. parable to the recent non-MSR components of With regard to technology development, a the Mars Exploration Program. key function of the program would be to pursue To minimize the impact on the breadth of new developments in partnership with other planetary science that NASA seeks to do other NASA elements and/or international space than at Mars, the required funding for this part agencies. For example, there could be some of the Mars Exploration Program would need crossover when developing technologies for to be added to the Planetary Sciences Division exploring the Mars polar caps and mid-latitude budget. The balance between exploration of ice and the icy satellites of the outer planets. Mars and of the rest of the solar system clearly As stated in the assumptions above, the depends on that budget. funding for this exploration would be in addi- However, there is much that we need to tion to that needed to finish MSR. The next learn about Mars, and Mars preserves the Mars flagships are likely to be driven at least in clues of a long and fascinating history. The an- part by the scientific yield of the analysis of the swers are there, exceptionally accessible to our returned samples. robotic missions and, ultimately, to humans op- erating safely on its surface.

60 Mars, the Nearest Habitable World October 2020 MASWG VI. A Mars Program Architecture for 2020–2035

Deltaic formation in Jezero Crater, the target for the Perseverance rover landing on Mars in February 2021. This false color image indicates different minerals, some produced by the action of water (e.g., implies material). (NASA Credit: CRISM / JHUAPL / JPL)

61 Mars, the Nearest Habitable World October 2020 MASWG VII. Implementing a Mars Exploration Program

VII. Implementing a Mars Exploration Program

Compelling scientific, programmatic, and benign. Mars is the logical next destination for technological arguments exist for NASA to humans to explore beyond the Earth-Moon sys- support a vigorous and robust Mars program tem. The value of infrastructure and synergis- that operates in addition to, and in parallel with, tic observations from orbiters, landers, and rov- the Mars Sample Return (MSR) program. ers has been demonstrated, both for mission In concert with the recommendations of Vi- safety and for mission science, by the ongoing sions and Voyages, MSR should proceed, as it Mars Exploration Program. The question is is the single effort at this time most likely to how to build on past success. produce a major step forward in our under- The challenge is how to explore Mars dur- standing of Mars. The analysis of returned ing a period when MSR and exciting non-Mars samples will have major implications for sci- missions will strain the current planetary sci- ence and for both robotic and human explora- ence budget. International partnering, as is be- tion missions to be launched in the 2030s and ing done for MSR, is one means of achieving beyond. The recent launch of Perseverance, what needs to be done, through partnerships which will prepare a cache of carefully selected that can leverage costs across multiple partners. and documented samples for future return, is a Commercial entities have already helped re- giant step forward in this endeavor. To address duce launch costs, and particular companies the remaining scientific objectives requires ad- have expressed interest in providing essential ditional flight missions as part of a program. services for Mars exploration. Ongoing devel- Scientifically, Mars provides the best op- opments in lunar exploration and the growing portunity to understand the development and number of space agencies sending missions to evolution of an Earth-like planet. Most of the Mars may lead the way for future collabora- processes and properties on terrestrial planets, tions, but these will require nurturing and pos- including interactions between geological, ge- sibly new business models for the challenges ophysical, climate/atmosphere, space weather, inherent in Mars exploration. and potential biological processes, can be One new development that should be ex- viewed on Mars today or interpreted from the ploitable early on is the ongoing rapid develop- physical and chemical records of past environ- ment in small-spacecraft capabilities. Their ap- ments. Among the solar system’s planets, in- plication to remote sensing from orbit is al- cluding Earth, Mars has the best-exposed and ready under study, and a critical development best-preserved 4-billion-year physical record. would be to show their ability to bring signifi- Sample return from the Jezero Crater environs cant science to the surface at much lower cost will provide a major contribution to interpret- than at present. The use of lower-cost missions ing that record, but in situ observations at other early on would help maintain progress on im- sites across the planet and their analysis are re- portant scientific questions during the develop- quired to answer fully the major questions of ment of those flight missions needed to return climate change and possible life origin on a samples cached by Perseverance. complex body that we now know to have been More capable missions (Discovery-class, habitable; i.e., one that has the necessary ingre- New Frontiers-class and eventually Flagship- dients for life. class missions again) will be needed to address Programmatically, Mars is accessible: By the most challenging objectives and discover- comparison to other planets, trip times are ies. All would benefit from a robust communi- short, and the surface environment is relatively cations infrastructure and advanced technology

62 Mars, the Nearest Habitable World October 2020 MASWG VII. Implementing a Mars Exploration Program that could augment data return and reduce land- This program would need the independence ing costs while improving landing precision. and access to science provided through the Sci- To pull all this together will require a con- ence Mission Directorate and its Planetary Sci- tinuing Mars Exploration Program, adequately ence Division. Where this leads in terms of fu- funded and sufficiently independent so that ture organizational structure is a subject for the missions can be selected within a long-term vi- future, especially should the national program sion of the science to be accomplished and the of exploring Mars with humans on the planet programmatic goals. Such a program would come into better focus. However, it is not too work with the science community to decide the early to pursue the compelling science ques- mission arcs to be pursued, to seed the technol- tions robotically while helping to enable and ogy investment needed to pursue that science shape the best use of future human activity on affordably, to work with international and com- Mars to answer the fundamental questions mercial partners, and to work with the human about Mars and what it can tell us about the exploration program to acquire useful other terrestrial planets, including Earth, and knowledge and flight experience, while build- planets beyond our solar system. ing the infrastructure required for implement- ing missions with humans.

63 Mars, the Nearest Habitable World October 2020 MASWG Appendices

Appendices

Sunset on Mars as observed from the Spirit . (Credit: NASA)

64 Mars, the Nearest Habitable World October 2020 MASWG Appendix A

Appendix A MASWG Meetings and Activities

MASWG utilized several opportunities to breadth and depth of mission concepts that collect input from specific projects and on spe- were being considered for future proposal op- cific topics, to obtain input from the commu- portunities. This was especially important in nity, and to solicit feedback on the preliminary the area of small-spacecraft mission concepts, draft of its report. These activities are summa- as the technical capabilities in that area have rized here. been evolving dramatically over the last couple Schedule—The MASWG charter was pro- of years and new science-mission concepts vided to the committee co-chairs, along with were being developed to take advantage of formal direction to proceed, in August 2019. them. We received ~55 papers, covering Committee candidates were identified and their the entire range of mission classes and science participation solicited. A planning meeting objectives. In order to protect proprietary was held on October 21–23, 2019, at which ideas, the community was promised that these preliminary topics to be developed were dis- white papers would be held as confidential, and cussed and plans for the committee were devel- thus not shared outside of MASWG, nor dis- oped. The first formal in-person meeting was cussed as specific concepts in any public fo- held on January 28–30, 2020. Additional in- rum; these promises were kept. person meetings were planned (and scheduled) Vetting—Preliminary results from the but had to be switched to virtual meetings due MASWG deliberations were made available to the COVID-19 pandemic. Two virtual meet- for review prior to our preparing the final re- ings of the entire committee were held April port. We presented them in PowerPoint form 20–22 and May 14–15, 2020. Additional to the Directors of the Planetary Science Divi- shorter meetings of the whole committee and sion and the Mars Exploration Program at splinter meetings of sub-groups of the commit- NASA Headquarters, and had a discussion with tee were held during this time frame in order to them about the emerging findings and recom- develop and vet ideas for our report. Updates mendations. We also presented the same Pow- on the status of the committee were presented erPoint package to a virtual meeting of at meetings of MEPAG on November 13, 2019; MEPAG on June 26, 2020. Feedback and input February 28, 2020; and , 2020. were received through discussion following the Activities—MASWG heard presentations at presentation and also through written feedback its in-person and virtual meetings on the status provided through an email site. of the NASA Mars program, science goals and In addition, we solicited formal reviews of objectives for Mars exploration, status of both the PowerPoint package from seven senior operational and in-development missions, mis- members of the Mars community. Together, sion concepts, technology development and ca- they included science, engineering, Mars mis- pabilities, human-mission development, com- sion, and programmatic backgrounds. mercial opportunities, PP, and mission cost ex- A final briefing to NASA Headquarters, ercises. These presentations included updates prior to delivery of the text report, was made on on those Planetary Mission Concept Studies October 28. (relevant to Mars) that were being supported by Input from all corners was considered in NASA through a different program. putting together this final report. Of course, In addition, MASWG solicited one-page MASWG takes full responsibility for the con- “mission concept” white papers from the com- tents of the report. munity to ensure that we were aware of the full

65 Mars, the Nearest Habitable World October 2020 MASWG Appendix B

Appendix B Science Contamination Control and Planetary Protection Considerations for the Future Mars Exploration Program

A future Mars Exploration Program as en- possible back contamination of the Earth’s bi- visioned by MASWG must deal with three ma- osphere. These concerns were codified in the jor constituencies in any set of policies that ad- Treaty of 1967 and have been in- dress contamination control and the legal terpreted and applied by NASA and the Com- framework of Planetary Protection (PP). mittee on Space Research (COSPAR) for more First, as befits a program that is grounded than 50 years. In brief, PP policy and practice in basic science, are the new investigations, in- address viable organisms. Scientific investiga- struments, and technologies emerging from the tions are concerned about confounding issues mission arcs described in the MASWG docu- in a given measurement, e.g., organic contami- ment. Science-driven exploration of former nants giving false readings in a highly sensitive (and potentially still) habitable environments spectrometer. will challenge PP policy and implementation as While PP policy and implementation have well as instrument design and cleaning. evolved over the years, there has been growing The second constituency, which has concern that NASA practice may have fallen emerged recently, are the spaceflight entrepre- behind current developments in biology and neurs, most notably Elon Musk’s Space Explo- not kept pace with the entrepreneurs and new ration Technologies Corp., or SpaceX. While plans for human exploration. To update current the bulk of the SpaceX business is in LEO and NASA policies, there have been three PP stud- occasional launches of communication satel- ies conducted within the past three years: lites to , it is the publicly • NASEM 2018, Planetary Protection Policy avowed focus on Mars that distinguishes Development Process (P3D) SpaceX from other entrepreneurial companies. • NASA Planetary Protection Independent In our MASWG report, we urge some pro- Review Board (PPIRB) 2019 grammatic experimentation with a Mars ver- • NASEM 2020, comparison of P3D 2018 sion of the lunar CLPS program. If such a pro- and PPIRB gram were to exist, those commercial providers Many issues were raised by the three stud- would be required to address a variety of con- ies, and for a complete understanding, one tamination issues. should consult the original documents. How- Third, to the surface of ever, for the purposes of MASWG, a few areas Mars, an old concept and an en- stand out as being worthy of special attention: gineering dream that dates at least to the 1948 In the PPIRB document, it was suggested writings (in German) of , that certain missions to parts of Mars might be brings concerns about contamination to a much recategorized as so-called Category II, where greater level. Humans carry billions of mi- only minimal reporting and an organic inven- crobes, and space suits invariably leak. Thus, tory is required. Currently, missions to Mars, any humans landing on Mars must exercise even orbiters, are categorized at least as Cate- great care in where they go, especially to any gory III, which carries with it the obligation for areas thought to be habitable or to have been substantial documentation, cleaning, and tra- habitable. jectory analysis. Missions that seek to land on As stated earlier, the core concern is con- Mars are typically Category IV, and a sample tamination by and amongst all three groups that return project is labeled Category V. Those may affect future scientific investigations and

66 Mars, the Nearest Habitable World October 2020 MASWG Appendix B latter categories require even more rigorous at- Mars). Thus, the NASEM 2020 study sug- tention. gested that NASA should evaluate whether PP The proposed recategorization of Mars costs are a burden on small spacecraft develop- missions was motivated in large part by com- ers and whether there is a cost floor for that mercial providers who quite understandably work. The NASEM study also suggested that would like to develop landing sites with mini- the NASA Office of Planetary Protection may mum requirements for cleaning and documen- help support small spacecraft providers with tation. However, given that the MASWG mis- some analysis. Given the importance of this sion arcs might include subsurface exploration topic, NASA should track this ongoing issue. and probing habitable areas, such a relaxation As stated in all three reports, PP requires a of scientific contamination or PP controls new independent advisory process. It is critical would require substantial study of the mission that Mars science be at the table and that this and its objectives before approval. In addition, new advisory process be coupled to any Mars as with human exploration, there would need to Exploration Program advisory group such as be a thorough examination of the operational MEPAG or the Planetary Advisory Committee. approach before any change in categories. One Finally, the special science contamination such proposal is to establish exploration/land- and PP issues raised by humans visiting Mars ing zones that could be sufficiently remote will require that science and human exploration from high-science value sites so that contami- work together to agree on which efforts (meas- nation is very unlikely. Research on this topic urements and missions) need to occur before is immature and requires substantial further ef- humans land on Mars. Among the important fort. topics is whether “exploration zones” can be A key element of our MASWG recommen- defined successfully. This requires research on dation is to incorporate small spacecraft into contamination control for both science and PP Mars exploration at the low-cost end of the to be funded and conducted. For back contam- spectrum. In the PPIRB report, it was alleged ination, biologists and physicians need to es- that small spacecraft face undue PP cost chal- tablish what human testing and quarantine is lenges. The NASEM 2020 report considered needed. that assertion and found some factual basis. For In summary, contamination control for sci- example, small organizations may not be able ence and new PP issues will need significant to afford the trajectory analysis that would ver- ongoing attention. ify (e.g., whether a flyby would indeed miss

67 Mars, the Nearest Habitable World October 2020 MASWG Appendix C

Appendix C Small-satellite Costs in the Context of Mars Exploration

Small Satellite missions deployed in Earth mass studies shown in Table C-1 may not be orbit are providing significant science at lower representative of the full range of possibilities costs. Their rapid development presents a new but still illustrates possible trends in a rapidly opportunity that could dramatically change the developing paradigm. cost of doing science at the Moon and in deep SIMPLEx-class missions are capped at space. Small-mission costs have been esti- $55M and Planetary Science Deep Space mated for a number of candidate missions in SmallSat Studies looked at mission concepts up Team-X studies at JPL. Including the launch to $100M. MASWG felt that these caps were vehicle but not Phase E, these costs are com- too restrictive for Mars missions, especially be- pared to actual mission costs for previously cause launch vehicle costs were not fully in- launched Mars missions in Table C-1. With cluded. The range used in this report for small many instruments shrinking in their mass and spacecraft missions was taken to be $100M– power needs, payload and spacecraft costs can 300M (Section VI). also be reduced. The candidate cost versus

Table C-1. Cost Estimates of Small to Large Mission. As-flown missions are compared with studies of small missions conducted by Team-X at JPL (Chad Edwards [JPL], personal communication, May 5, 2020). InSight (NSYT) and MSL costs include impacts of 2-year launch slips. Phase E costs not included. Several factors (e.g., requirements for mission lifetime, margin policies) vary between studies. 1

1 Note: Mission cost assumptions in this document are of a budgetary and planning nature and are intended for informational purposes only. They do not constitute a commitment by NASA.

68 Mars, the Nearest Habitable World October 2020 MASWG Appendix D

Appendix D References

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77 Mars, the Nearest Habitable World October 2020 MASWG Appendix E

Appendix E Acronym List

3D Three-dimensional HiRISE (MRO) High-Resolution AO Announcement of Imaging Science Opportunity Experiment CCP Commercial Crew Program HVM3 High-resolution Volatiles CLPS Commercial Lunar Payload and Minerals Moon Services Mapper CNSA China National Space IDIQ Indefinite Delivery, Administration Indefinite Quantity CoMPS Commercial Mars Payload InSight Interior Exploration using Services Seismic Investigations, COSPAR Committee on Space Geodesy, and Heat Research Transport COTS Commercial Orbital ISRO Indian Space Research Transportation Services Organisation CRISM (MRO) Compact ISRU In Situ Resource Reconnaissance Imaging Utilization Spectrometer for Mars ISS International Space Station CRS Cargo Resupply Services JAXA Japan Aerospace CTX (MRO) Context Camera Exploration Agency DSc Discovery class JPL Jet Propulsion Laboratory DSN Deep Space Network JSC EDL Entry, Descent, and LEO Low-Earth Orbit Landing Ma Million years (age of EM Electromagnetic materials) EMM (UAE) Emirates Mars M2020 Mars 2020 mission Mission MarCO Mars Cube One ESA European Space Agency MARSIS (MEX) Mars Advanced EscaPADE Escape and Plasma Radar for Subsurface and and Sounding Dynamics Explorers MASWG Mars Architecture Strategy ExoMars (ESA) Exobiology Mars Working Group FLG Flagship Class MAV Mars Ascent Vehicle GEO Geostationary Orbit MAVEN Mars Atmosphere and GRAIL Gravity Recovery and Volatile EvolutioN Interior Laboratory MEDA (M2020) Mars Environmental Dynamics GSFC Goddard Space Flight Analyzer Center MEP Mars Exploration Program Gyr Billion years MEPAG Mars Exploration Program HEOMD (NASA) Human Exploration and Operations Analysis Group Mission Directorate

78 Mars, the Nearest Habitable World October 2020 MASWG Appendix E MER Mars Exploration Rover PI Principal Investigator (Spirit & Opportunity) PLD Polar Layered Deposits MEX (ESA) Mars Express PP Planetary Protection Mission PPIRB Planetary Protection MGS Independent Review Board mission PREFIRE Polar Radiant Energy in MOC (MGS) Mars Orbiter the Far Infrared Camera Experiment MOXIE (M2020) Mars Oxygen In- PSDS3 Planetary Science Deep Situ Resource Utilization Space SmallSat Studies Experiment R&A Research and Analysis MPIAT Mars Program Independent RFI Request for Information Assessment Team RIMFAX (M2020) Radar Imager for MPO Mars Program Office Mars’ Subsurface MRO Mars Reconnaissance Exploration Orbiter ROI Return on Investment MSL SAA Space Act Agreement (Curiosity) SHARAD (MRO) Shallow Radar MSR Mars Sample Return experiment NASA National Aeronautics and SIMPLEx Small Innovative Missions Space Administration for Planetary Exploration NASEM National Academies of SMD (NASA) Science Mission Science, Engineering, and Directorate Medicine SpaceX NFc New-Frontiers class Technologies Corporation NID NASA Interim Directive SSc Small-Spacecraft Class NPR NASA Procedural SWIM Subsurface Water Ice Requirement Mapping NRA NASA Research TES (MGS) Thermal Emission Announcement Spectrometer NRC National Research Council TGO (ESA) OMEGA (MEX) Observatoire pour THEMIS (ODY) Thermal Emission la Mineralogie, l’Eau, les Imaging System Glaces, et l’Activite UAE SA United Arab Emirates ODY Mars Odyssey Orbiter Space Agency P3D Planetary Protection Policy XUV Extreme Development Process PHX Phoenix Lander

79 Mars, the Nearest Habitable World October 2020 MASWG Appendix F

Appendix F Acknowledgments

A report such as this one requires a tremen- Nathan Barba, Bob Bruner, Barbara Cohen, dous effort on the part of a large number of peo- Serina Diniega, Colin Dundas, Abigail ple in addition to the committee members. We Fraeman, Anthony Freeman, Marc Fries, are grateful for the support we’ve received Andrew Good, Bob Grimm, Jim Head, Jeff from the following people: Johnson, John Karcs, James Kaufman, Ed- • Members of the Mars and broader commu- win Kite, Armin Kleinboehl, Rob Lillis, nity who presented material to and inter- Timothy McConnochie, Alfred McEwen, acted with the committee. In addition to Carolyn Mercer, Michelle Minitti, Michael some presentations by committee members, Mischna, Luca Montabone, Claire New- presentations were given by Don Banfield, man, Horton Newsom, John Rummel, Steve Penny Boston, Bobby Braun, Bruce Camp- Ruff, Isaac Smith, Adam Schilffarth, Andy bell, , Alfonso Davila, Rick Spry, Vlada Stamenkovic, Leslie Tamppari, Davis, David Des Marais, Serina Diniega, and Tim Titus. Lindsey Hays, Rob Lillis, Michael Meyer, • People who formally reviewed our prelimi- Charles Norton, , Louise Prockter, nary report as presented to MEPAG in chart Jim Watzin, Ken Williford, and Paul form, on short notice and with rapid turna- Wooster. round and insightful comments—Michael • Chad Edwards from JPL, who provided a Carr, David DesMarais, Nicholas Jedrich, summary and analysis of Mars mission costs Mark Saunders, Stuart Spath, Aileen Yingst, at our request. and A. Thomas Young. • Members of the Mars community who pro- • Serina Diniega for support to the committee vided feedback on our MEPAG presenta- above and beyond what was required and for tion, either in the discussion at the time of valuable input into the committee discus- the presentation or in written form later. sions. Hopefully, we aren’t missing anybody; this • Kristine McGowan, for documentation ser- included Michael Aye, W. Bruce Banerdt, vices.

Government sponsorship of the Mars Architecture Strategy Working Group is acknowledged, supported by the National Aeronautics and Space Administration through contracts with Cornell Technical Services and with the Jet Propulsion Laboratory, California Institute of Technology.

80 Mars, the Nearest Habitable World October 2020 MASWG

Artist's rendering of a solar storm hitting Mars and stripping ions from the planet's upper atmosphere, based on results from the MAVEN mission. (Credit: CU/LASP and NASA)

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