51st Lunar and Planetary Science Conference (2020) 2077.pdf

ASSESSING THE HABITABILITY OF AN ACTIVE OCEAN WORLD: THE ETNA MISSION CONCEPT TO EXPLORE ENCELADUS’ TIGER STRIPES. Chandrakanth Venigalla1, Ariel N. Deutsch2, Paolo Panicucci3,4,5, Graciela González Peytaví6, Jennifer Pouplin7, Laura Tenelanda-Osorio8, Andrea Guarriello9,10, Emili- ano Castillo Specia11, Yun-Hang Cho12, Victoria Da-Poian3, Onalli Gunasekara13, Lewis Jones14, Mariya Krasteva15, Thasshwin Mathanlal16, Nicole Villanueva17, Sam Zaref18, 1University of Colorado, USA (Chandrakanth.Veni- [email protected]), 2Brown University, USA, 3ISAE-SUPAERO, France, 4Centre National d'Etudes Spatiales, France, 5Airbus Defence & Space, France, 6Universitȁt der Bundeswehr, Germany, 7Purdue University, USA, 8Uni- versidad Eafit, Colombia, 9Heriot-Watt University, UK, 10Institut d'Électronique et de Télécommunications de Rennes, France, 11Tecnologico de Monterrey, Mexico, 12University of Sheffield, UK, 13University of Illinois Urbana-Cham- paign, USA, 14California Institute of Technology, USA, 15Concordia University, Canada, 16Luleå University of Tech- nology, Sweden, 17Pontificia Universidad Católica del Perú, Perú, 18Rhode Island School of Design, USA.

Introduction: The presence of contemporary habi- Science goals: The Etna mission is designed to ad- tats elsewhere in the Solar System with the ingredients dress two overarching science goals, responding to two necessary to sustain life [1] is one of the strongest driv- of the three identified cross-cutting science themes of ers of exploration. Do such habitats exist, and do organ- the Decadal Survey: Planetary habitats and Building isms live there now? One of the most promising targets new worlds. The first science goal of Etna is to under- to explore these questions is Enceladus – an icy world stand how Enceladus provides habitable conditions. To where a liquid water ocean exists between a dynamic accomplish this goal, Etna will (1) constrain the dynam- icy shell and a potentially active silicate interior [2–6]. ics of the energy sources that drive surface and sub-sur- Enceladus, one of Saturn's moons, became a com- face interactions, (2) assess the chemistry and bulk com- pelling target when Voyager [7] revealed it to be our position of the subsurface, and (3) analyze the periodic- Solar System's most reflective body, suggesting that the ity and lifetime of habitable conditions. This goal ad- surface is composed of fresh snow or ice [3, 8–9]. The dresses primary questions in the Decadal Survey regard- Cassini spacecraft subsequently imaged active plumes ing the primordial sources of organic matter, possible erupting material sourced from beneath the moon's locations of ongoing organic synthesis, and locations of south polar crust and expelling it tens of kilometers into contemporary habitable environments [1]. Understand- the atmosphere [5], revealing Enceladus as an active ing the moon accretion model for Enceladus is relevant world, likely to be driven by subsurface geothermal ac- to addressing the habitable conditions of the moon in tivity [6]. The Cassini mass spectrometer detected four order to constrain the origin and evolution of volatiles important biogenic elements coincident with the build- and organics in the Enceladus system, such as whether ing blocks of terrestrial life: H, C, O and N [4]. How- these interior materials are primordial, derived from ac- ever, the limited resolution of the Cassini instrument cretion or produced via chemical reactions such as ser- [10] prevented the detection of P and S: the two addi- pentinization or Fischer-Tropsch reactions [11]. tional key biomarkers of Earth-based life that are critical The second science goal of Etna is to characterize in assessing astrobiological potential. Thus, questions the biotic and abiotic signatures of Enceladus. Etna will remain related to the habitability of Enceladus. (1) characterize the composition, structure, and ratio of The coincident presence of an energy source, a cat- subsurface molecules, (2) determine the presence of vis- alyst for life, and the building blocks of Earth-like life ual biomarkers in the Tiger Stripes ejecta, and (3) deter- promotes Enceladus as a paramount target for studying mine how H, C, O, and N are produced. This goal di- the origin and evolution of habitable conditions and life rectly addresses the Decadal Survey’s priority of deter- throughout our Solar System. Among all of the other mining whether any extra-terrestrial habitats are or ever ocean worlds in our Solar System, Enceladus is the only have been occupied by organisms [1]. This science goal active body that provides direct access to its ocean also directly addresses one of the four Science Ques- through the expulsion of subsurface material. tions identified by NASA’s Science Mission Directorate Etna is a mission concept designed and proposed as the motivation for Solar System exploration: “How during the 5th Caltech Space Challenge 2019 (spacechal- did life begin and evolve on Earth, and has it evolved lenge.caltech.edu) in order to "assess whether Encela- elsewhere in the Solar System?” dus provides the conditions necessary (or sufficient) to Instrumentation: The mission payload consists of sustain biotic or pre-biotic chemistry.” In Greek mythol- six scientific instruments (Table 1), split between an or- ogy, Enceladus was struck down during an epic battle biter and a lander, selected to fulfill the scientific goals for control of the cosmos and buried under Mount Etna, of the mission. All of the instruments have high TRL where the Giant is trapped today. 51st Lunar and Planetary Science Conference (2020) 2077.pdf

with the exception of the geophones, which were ex- The geophone probes (Fig. 2) are spun up along axis plored as a component of our design challenge. and released from the orbiter during descent. Shock ab- Instrument Goal 1 Goal 2 Phase sorbers, designed for impacting a hard surface, mitigate Ultra-Violet Imaging X O the landing impact. In the case of snow-covered ground, Spectrograph the probes extend their Storable Tubular Extendible Optical Camera X O Member (STEM) into the surface until contact is made Radio Science X O with a hard surface. This allows the seismic vibrations Ion Microscope + Mass X X F, L (otherwise damped out by the snow) to be observed by Spectrometer the probe. From the top end of the probe, the Telescopic Temperature Sensors X F, L Tubular Mast (TTM) is deployed. This 1.5-m antenna Geophone Surface X L will clear the surface to allow communication with the Probes orbiter, even during precipitation events. Temperature Table 1. Science payload. The mission phase is denoted by O control of the instruments is managed by an insulating for orbital, F for plume fly-through, and L for landed. layer of aerogel and an internal resistive heater. Two LP Mission architecture: The Etna spacecraft (Fig. 1) 33330 6Ah batteries are used as power sources and pro- consists of a single orbiter, a single lander, and three vide sufficient power for the threshold of one week op- geophone surface probes (Fig. 2) that form a network of distributed landers. erational life of the probes.

Fig. 2. Diagram of an Etna geophone surface probe. Conclusions: Enceladus is unique Solar System tar- get because of the coincident presence of energy cata- Fig. 1. The orbiter, housing the lander and surface probes. lysts and the building blocks of Earth-like life, and be- The Orbiter. The orbiter (Fig. 1) will be placed in the cause active plumes provide unparalleled access to its Saturn-Enceladus system to conduct remote science, subsurface ocean. The Etna mission concept provides a finalize the precise landing location, and relay data from feasible architecture to explore Enceladus as a means of the landed assets back to Earth. It will also conduct fly- better understanding the origin and evolution of habita- throughs of the active plumes. The orbiter incorporates bility and life. a variety of subsystems with high TRL components, a Acknowledgements: We thank S. Toedtli, F. Royer, N. Juno-heritage propulsion system, and RTG-provided Angold, M. Cable, T. Heinsheimer, T. Nordheim, J.-P. de la power. The lander stays attached to the orbiter for early Croix, J. Karras, D. Murrow, G. Meiron-Griffith, and JPL’s science operations, then is released from the orbiter for A-Team for their mentorship, and Lockheed Martin, Keck In- surface science operations. stitute for Space Sciences, Northrop Grumman, Aerospace The Lander. Etna includes a robust soft lander that is Corporation, JPL, GALcit, the Moore-Hufstedler Fund, and radiation tolerant. Design drivers for the lander include Caltech for their support. All artwork is by Sam Zaref. the need for a soft and upright landing, the ability to use References: [1] Squyres S. W. et al. (2011) Nat. Res. Nat. the same instrument package (Ion Microscope + Mass Acad. [2] Parkinson C. D. et al. (2008) Orig. Life Evol. Bio- Spectrograph) both in-orbit and on the surface, and the sph., 38, 355–369. [3] Brown R. H. et al. (2006) Science, 311, need to deploy the geophone probes during descent to 1425–1528. [4] Porco C. C. et al. (2006) Science, 311, 1393– the surface. 1401. [5] Hansen C. J. et al. (2006) Science, 311, 1422–1425. The Surface Probes. An important component of our [6] Spencer J. R. and Nimmo F. (2013) Ann. Rev. of Earth and driving science is related to the dynamics, periodicity, Planet. Sci., 41, 693–717. [7] Smith B. A. et al. (1982) Sci- and lifetime of habitable conditions. We developed ge- ence, 215, 504–537. [8] Cruikshank D. P. (1980) Icarus, 41, ophone surface probes with the purpose of characteriz- 246–258. [9] Verbiscer A. J. et al. (2005) Icarus, 173, 66–83. ing the dynamics of the icy crust and constraining dom- [10] Postberg F. et al. (2011) Nature, 474, 620. [11] Matson D. L. et al. (2009) Springer, 577–612. inant stress directions, magnitudes, and timescales in the South Polar Terrain.