The aim of this study is to give the next Decadal Survey panel a viable alternative or addition to sample In Situ Geochronology for the Next Decade: return missions to accomplish longstanding geochronology goals within a New Frontiers envelope. • Absolute ages for multiple worlds are a desire in both the 2003 and 2013 Planetary Science Decadal A Planetary Mission Concept Study Surveys, but in these two decades, only sample return was considered a viable method for geochronology. PI: Barbara A. Cohen, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA The Decadal Surveys recommended mission lists reflect the reality for those decades that sample return is (Barbara.A.Cohen@nasa.gov) the only way to yield reliable and interpretable geochronology. Our Science Definition Team comprises a diverse team of geologists and geochronologists • In the last two decades, NASA has invested in the development of in situ dating techniques, increasing the with expertise across the Moon, Mars, and small bodies to represent inner Solar System maturity of instruments using complementary radiogenic isotopic systems (K-Ar and Rb-Sr) to TRL 6. science.: Kris Zacny, Honeybee Robotics; Kelsey Young, NASA Goddard Space Flight Center; R. Aileen Yingst, Planetary Science Institute; Tim Swindle, University of Arizona; Stuart Robbins, • The time is right to consider how the precision achievable with in situ geochronology can advance Southwest Research Institute; Jennifer Grier, Planetary Science Institute; John Grant, important science goals for the next Decadal Survey Smithsonian Institution; Caleb Fassett, NASA Marshall Space Flight Center; Ken Farley, Current Element Objective Heritage Mass (kg) Power (W) California Institute of Technology; Bethany Ehlmann, California Institute of Technology; TRL Darby Dyar, Planetary Science Institute; Carolyn van der Bogert, University of Münster; KArLE K-Ar geochronology PIDDP and DALI 25 65 (peak) 6* Ricardo Arevalo, University of Maryland; F. Scott Anderson, Southwest Research Institute PIDDP and CDEX Rb-Sr geochronology 50 180 (peak) 6* MatISSE Trace-element ICP-MS PIDDP 25 3 Major advances in understanding formation and evolution of the inner solar system can geochemistry Point or Sample selection and MicrOmega (ESA), be driven by absolute geochronology in the next decade: calibrating body-specific 2 to 3 24 6* imaging characterization, NIRVSS (NPLP) chronologies and creating a framework for understanding Solar System formation, the spectrometer geologic context Geologic context, MER MI/Pancam, effects of impact bombardment on life, and the evolution of planets and interiors. 9 for Mars workspace MSL Potential Cameras 2 (for 2) 4 and Moon documentation, sample MAHLI/Mastcam, Science Small Bodies solutions asteroids (SCEM/ASM- Mars (iMOST) characterization WATSON Drivers (SBAG) (illustrative, not SAT) definitive) Acquire and sort 6 for PlanetVac MMX regolith samples asteroids 1a. Determinethe 1.2.3. Use the Sample triage Introduce samples to age of lunar distribution of SAM carousel (MSL) 10 TBD 9 for Mars and analysis analysis instruments basins; 1b. compositions and Absolute ages of carousels Anchor the early ages of small large planetary Total 105 180 (peak) Impacts and Earth-Moon 3. Determine the bodies to make basins (e.g. South Solar System impact flux curve evolutionary testable Pole-Aitken, *these instruments are currently funded for development to TRL 6 through NASA and ESA instrument development programs; no dynamics by determining timeline of Mars. predictions about Nectaris, Isidis, additional costs would be required to achieve this TRL rating. MatISSE - Maturation of Instruments for Solar System Exploration, the age of SPA observable Caloris, DALI - Development of Advanced Lunar Instrumentation, NPLP - NASA-Provided Lunar Payloads Basin; 1d. Assess parameters in Rheasilvia) the recent impact forming planetary This study will formulate and cost a medium- or flagship-class mission for Solar System chronology flux. systems. • Science Definition Team (SDT) will identify the most important science questions that can be answered in the next decade using the first generation of in situ dating techniques and examine 1.4.3. Determine 5b. Determine the the evolution of Correlate mission-level requirements, trades, and instrumentation for answering these questions age of the the interiors of crystallization age youngest and • Notional payload includes two geochronology techniques (Rb-Sr and K-Ar), sample acquisition and 1.5 Determine the small bodies, of igneous rocks Igneous oldest mare petrogenesis of including from a wide range handling, and contextual measurements evolution and basalts; 5d. martian igneous differentiation and of geographic interior Determine the • Mission trades include mobility, number of samples and sites required, operations timelines, and rocks in time and melting, locations with processes flux of lunar space. metamorphism, petrology, mission architecture choices. Going-in positions for this study are in bold but could change in volcanism and its and mineralogy, and evolution through concert with the Mission Design activity. fragmentation/ composition. space and time. reaccretion.

Determine the 4b. Determine the 4.0 Constrain the radiometric ages Topic Trades source(s) for inventory of of unhydrated Destination • Moon - Pre-Imbrian basin impact melt, youngest basalt lunar polar martian volatiles 1.3.4. Use ages of primary materials • Mars - Noachian potentially habitable crust , keystone Hesperian lava flow volatiles. 7c. as a function of meteorites and and hydrated Habitability Understand geologic time and returned samples • Vesta - Rheasilvia and Veneneia basins secondary and delivery regolith determine the to determine the materials. Sampling Regolith/pneumatic vs rock/drill design; sample handling and presentation pathways; amount of workspace of volatiles modification ways in which most recent Determine the required processes, these volatiles dynamical history timescales of particularly have interacted of these objects. Landing • Passive delivery of deposition of with Mars as a • Terrain-relative navigation (identify existing map products) volatile-bearing volatile materials. geologic system. • materials. Active hazard avoidance Mobility • Local - single lander

Calibrate the • Regional – rover 5.0 Reconstruct 1.2.2. Determine cratering • Global - multiple landers and/or a hopper Calibrating the history of the timing of chronology Operations Sample acquisition and delivery operations run with ground in the loop or autonomously, fault tolerance for absolute 1c. Establish a Mars as a planet, events in the across multiple ages across precise absolute the origin and early Solar bodies by dating sample acquisition and delivery, sample analysis decision rules (e.g., geochronology systems not agreeing or the Solar chronology. modification of System, using surfaces with converging) System the crust, mantle meteorites and well-defined and core. returned samples cratering Mission Sizing of lander, power (solar + battery vs nuclear), common elements (C&DH, comm, etc.) statistics.