Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022)

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Prepublication Copy – Subject to Further Editorial Correction Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 Committee on the Planetary Science and Astrobiology Decadal Survey Space Studies Board Division on Engineering and Physical Sciences A Consensus Study Report of PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 

THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001 This study is based on work supported by the Contract No. NNH17CB02B/NNH17CB01T with the National Aeronautics and Space Administration and and Grant No. 2040016 with the National Science Foundation. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any agency or organization that provided support for the project. International Standard Book Number-13: XXX-X-XXX-XXXXX-X International Standard Book Number-10: X-XXX-XXXXX-X Digital Object Identifier: https://doi.org/10.17226/26522 Copies of this publication are available free of charge from: Space Studies Board National Academies of Sciences, Engineering, and Medicine 500 Fifth Street, NW Washington, DC 20001 Additional copies of this publication are available from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242 or (202) 334-3313; http://www.nap.edu. Copyright 2022 by the National Academy of Sciences. All rights reserved. Printed in the United States of America Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2022. Origins, Worlds, Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032. Washington, DC: The National Academies Press. https://doi.org/10.17226/26522. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 

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COMMITTEE ON THE PLANETARY SCIENCE AND ASTROBIOLOGY DECADAL SURVEY Steering Group ROBIN M. CANUP, NAS, Southwest Research Institute, Co-Chair PHILIP R. CHRISTENSEN, Arizona State University, Co-Chair MAHZARIN R. BANAJI, NAS, Harvard University STEVEN BATTEL, NAE, Battel Engineering LARS BORG, Lawrence Livermore National Laboratory ATHENA COUSTENIS, National Centre for Scientific Research JAMES CROCKER, NAE, Lockheed Martin Space Systems Company BRETT DENEVI, Johns Hopkins Applied Physics Laboratory BETHANY EHLMANN, California Institute of Technology LARRY ESPOSITO, University of Colorado Boulder ORLANDO FIGUEROA, Orlando Leadership Enterprise, LLC JOHN GRUNSFELD, Endless Frontier Associates, LLC JULIE HUBER, Woods Hole Oceanographic Institution KRISHAN KHURANA, University of California, Los Angeles WILLIAM MCKINNON, Washington University, St. Louis FRANCIS NIMMO, NAS, University of California Santa Cruz CAROL RAYMOND, Jet Propulsion Laboratory BARBARA SHERWOOD LOLLAR, NAS/NAE, University of Toronto AMY SIMON, NASA Goddard Space Flight Center Panel on Giant Planet Systems JONATHAN LUNINE, NAS, Cornell University, Chair AMY SIMON, NASA Goddard Space Flight Center, Vice Chair FRANCES BAGENAL, NAS, University of Colorado, Boulder RICHARD DISSLY, Ball Aerospace and Technologies LEIGH FLETCHER, University of Leicester TRISTAN GUILLOT, Nice Observatory MATTHEW HEDMAN, University of Idaho RAVIT HELLED, University of Zurich KATHLEEN MANDT, Johns Hopkins University, Applied Physics Laboratory ALYSSA RHODEN, Southwest Research Institute PAUL SCHENK, Lunar and Planetary Institute MICHAEL WONG, SETI Institute Panel on Ocean Worlds and Dwarf Planets ALEXANDER HAYES, Cornell University, Chair FRANCIS NIMMO, NAS, University of California Santa Cruz, Vice Chair MORGAN CABLE, Jet Propulsion Laboratory ALFONSO DAVILA, NASA Ames Research Center GLEN FOUNTAIN, Johns Hopkins University APL CHRISTOPHER GERMAN, Woods Hole Oceanographic CHRISTOPHER GLEIN, Southwest Research Institute CANDICE HANSEN, Planetary Science Institute EMILY MARTIN, National Air and Space Museum MARC NEVEU, University of Maryland CAROL PATY, University of Oregon LYNNAE QUICK, NASA Goddard Space Flight Center JASON SODERBLOM, Massachusetts Institute of Technology KRISTA SODERLUND, University of Texas Institute for Geophysics PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION v 

Panel on Mercury and the Moon TIMOTHY L. GROVE, NAS, Massachusetts Institute of Technology, Chair BRETT DENEVI, Johns Hopkins University, Applied Physics Laboratory, Vice Chair JAMES DAY, University of California San Diego ALEXANDER EVANS, Brown University SARAH FAGENTS, University of Hawaii at Manoa WILLIAM FARRELL, NASA Goddard Space Flight Center CALEB FASSETT, NASA Marshall Space Flight Center JENNIFER HELDMANN, NASA Ames Research Center MASATOSHI HIRABAYASHI, Auburn University JAMES TUTTLE KEANE, Jet Propulsion Laboratory FRANCIS MCCUBBIN, NASA Johnson Space Center MIKI NAKAJIMA, University of Rochester MARK SAUNDERS, Consultant SONIA TIKOO-SCHANTZ, Stanford University Panel on Mars VICTORIA HAMILTON, Southwest Research Institute, Chair BETHANY EHLMANN, California Institute of Technology, Vice Chair WILLIAM BRINCKERHOFF, NASA Goddard Space Flight Center TRACY GREGG, University of Buffalo JASPER HALEKAS, University of Iowa JOHN HOLT, University of Arizona JOEL HUROWITZ, Stony Brook University BRUCE JAKOSKY, University of Colorado Boulder MICHAEL MANGA, NAS, University of California Berkeley HARRY MCSWEEN, NAS, University of Tennessee CLAIRE NEWMAN, Aeolis Research ALEJANDRO SAN MARTIN, NAE, Jet Propulsion Laboratory KIRSTEN SIEBACH, Rice University AMY WILLIAMS, University of Florida ROBIN WORDSWORTH, Harvard University Panel on Venus PAUL BYRNE, Washington University, St. Louis, Chair LARRY ESPOSITO, University of Colorado, Vice Chair GIADA ARNEY, NASA Goddard Space Flight Center AMANDA BRECHT, NASA Ames Research Center THOMAS CRAVENS, University of Kansas KANDIS LEA JESSUP, Southwest Research Institute JAMES KASTING, NAS, Pennsylvania State University SCOTT KING, Virginia Polytechnic Institute and State University BERNARD MARTY, Universite de Lorraine THOMAS NAVARRO, University of California Los Angeles JOSEPH O’ROURKE, Arizona State University JENNIFER ROCCA, Jet Propulsion Laboratory ALISON SANTOS, Wesleyan University JENNIFER WHITTEN, Tulane University PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION vi 

Panel on Small Solar System Bodies NANCY CHABOT, Johns Hopkins University, Applied Physics Laboratory, Chair CAROL RAYMOND, Jet Propulsion Laboratory, Vice Chair PAUL ABELL, NASA Johnson Space Center WILLIAM BOTTKE, Southwest Research Institute HAROLD CONNOLLY, Rowan University THOMAS JONES, Association of Space Explorers STEFANIE MILAM, NASA Goddard Space Flight Center EDGARD RIVERA-VALENTIN, Lunar and Planetary Institute DANIEL SCHEERES, NAE, University of Colorado Boulder RHONDA STROUD, Naval Research Laboratory MEGAN BRUCK SYAL, Lawrence Livermore National Laboratory MYRIAM TELUS, University of California Santa Cruz AUDREY THIROUIN, Lowell Observatory CHAD TRUJILLO, Northern Arizona University BENJAMIN WEISS, Massachusetts Institute of Technology Staff DAVID H. SMITH, Senior Program Officer, Space Studies Board, Study Director DWAYNE A. DAY, Senior Program Officer, Aeronautics and Space Engineering Board DANIEL NAGASAWA, Program Officer, Space Studies Board JORDYN WHITE, Program Officer, Committee on National Statistics MIA BROWN, Research Associate, Space Studies Board MEGAN A. CHAMBERLAIN, Senior Program Assistant, Space Studies Board GAYBRIELLE HOLBERT, Program Assistant, Space Studies Board KATHERINE DZURILLA, Temporary Research Assistant, Space Studies Board LUCIA ILLIARI, Temporary Research Assistant, Space Studies, Board JEAN DE BECDELIEVRE, Christine C. Mirzayan Science and Technology Policy Fellow (2021) JACOB ABRAHM, Lloyd V. Berkner Space Policy Intern (2021) TARINI KONCHADY, Lloyd V. Berkner Space Policy Intern (2021) COLLEEN N. HARTMAN, Director, Space Studies Board PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION vii 

SPACE STUDIES BOARD MARGARET G. KIVELSON, NAS, University of California, Los Angeles, Chair GREGORY P. ASNER, NAS, Carnegie Institution for Science ADAM BURROWS, NAS, Princeton University JAMES H. CROCKER, NAE, Lockheed Martin Space Systems Company (Retired) JEFF DOZIER, University of California, Santa Barbara MELINDA DARBY DYAR, Mount Holyoke College ANTONIO L. ELIAS, NAE, Orbital ATK, Inc. (retired) VICTORIA HAMILTON, Southwest Research Institute DENNIS P. LETTENMAIER, NAE, University of California, Los Angeles ROSALY M. LOPES, Jet Propulsion Laboratory STEPHEN J. MACKWELL, American Institute of Physics DAVID J. MCCOMAS, Princeton University LARRY J. PAXTON, Johns Hopkins University ELIOT QUATAERT, University of California, Berkeley MARK SAUNDERS, NASA (retired) BARBARA SHERWOOD LOLLAR, NAS/NAE, University of Toronto HOWARD SINGER, National Oceanographic and Atmospheric Administration ERIKA B WAGNER, Blue Origin, LLC PAUL D. WOOSTER, Space Exploration Technologies EDWARD L. WRIGHT, NAS, University of California, Los Angeles Staff COLLEEN N. HARTMAN, Director CARMELA J. CHAMBERLAIN, Administrative Coordinator TANJA PILZAK, Manager, Program Operations CELESTE A. NAYLOR, Information Management Associate MARGARET KNEMEYER, Financial Officer PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION viii 

Preface The Planetary Science Division (PSD) of NASA’s Science Mission Directorate (SMD) is the primary source of funding of planetary science, astrobiology, and planetary defense activities in the United States. In addition, the National Science Foundation (NSF) provides modest, but highly important, support for a variety of supporting ground-based activities; most notably access to world-class, ground-based optical and radio telescopes. The allocation of resources within and between spacecraft missions, supporting research activities, and technology development is determined to a major extent via a relatively mature strategic planning process that relies heavily on inputs from the scientific community to establish the scientific basis and direction for its space-science flight- and ground-research programs and technology development activities. The primary sources of this guidance are the independent scientific analyses and recommendations provided by reports of the National Academies of Sciences, Engineering, and Medicine (e.g., by the Space Studies Board (SSB) and its committees) and, to a lesser extent, by parallel inputs coming from community- based, but NASA-organized, analysis/assessment groups (e.g., the Mars Exploration Program Analysis Group and the Outer Planets Assessment Group). The science strategies developed by the SSB and the analysis/assessment groups form input to subsequent program development activities conducted by the FACA-chartered NASA Advisory Council and its associated committees (e.g., NASA’s Planetary Science Committee). The SSB’s primary vehicles for the provision of strategic advice to NASA are the space science decadal surveys. The National Academies’ decadal surveys are widely recognized among policymakers and program managers as a key resource in determining where a field of research is and where it is headed. Indeed, the decadal survey process has proved so useful that the Section 1104 of the NASA Authorization Act of 2008 requiring that the NASA “Administrator shall enter into agreements on a periodic basis with the National Academies for independent assessments, also known as decadal surveys, to take stock of the status and opportunities for Earth and space science discipline fields and Aeronautics research and to recommend priorities for research and programmatic areas over the next decade.” The most recent effort for planetary science and astrobiology resulted in the publication of Vision and Voyages for Planetary Science in the Decade 2013-2022 in 2011. While it is generally regarded that Vision and Voyages was especially successful in its outcomes—as witnessed by the facts that the survey’s top two large-class mission priorities are both under development and that PSD’s annual budget has doubled over the last decade—a new survey is needed to address the challenges of the coming decade. Following informal requests in the early months of 2019 from the director of PSD, the SSB and its Committee on Astrobiology and Planetary Science (CAPS) began the task of defining the specific actions and issues that needed to be address in a new decadal survey. CAPS’s activities culminated in the convening of a decadal survey organizing meeting, held at the California Institute of Technology’s Keck Institute of Space Science in September 2019. Negotiations between NASA and the SSB continued through the final months of 2019 and eventually settled upon a statement of task calling for a decadal survey that provided a clear exposition of the following: 1 1 See Appendix A for the letter requesting this study, the full text of the statement of task and additional, non- binding guidelines. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION ix 

1. An overview of planetary science, astrobiology, and planetary defense: what they are, why they are compelling undertakings, and the relationship between space- and ground- based research; 2. A broad survey of the current state of knowledge of the solar system; 3. The most compelling science questions, goals and challenges which should motivate future strategy in planetary science, astrobiology, and planetary defense; 4. A coherent and consistent traceability of recommended research and missions to objectives and goals; 5. A comprehensive research strategy to advance the frontiers of planetary science, astrobiology and planetary defense during the period 2023-2032 that will include identifying, recommending, and ranking the highest priority research activities (research activities include any project, facility, experiment, mission, or research program of sufficient scope to be identified separately in the final report).For each activity, consideration should be given to the scientific case, international and private landscape, timing, cost category and cost risk, as well as technical readiness, technical risk, lifetime, and opportunities for partnerships. The strategy should be balanced, by considering large, medium, and small research activities for both ground and space; 6. Recommendations for decision rules, where appropriate, for the comprehensive research strategy that can accommodate significant but reasonable deviations in the projected budget or changes in urgency precipitated by new discoveries or technological developments; 7. An awareness of the science and space mission plans and priorities of NASA human space exploration programs and potential foreign and U.S. agency partners reflected in the comprehensive research strategy and identification of opportunities for cooperation, as appropriate; 8. The opportunities for collaborative research that are relevant to science priorities between SMD’s four science divisions (for example, comparative planetology approaches to exoplanet or astrobiology research); between NASA SMD and the other NASA mission directorates; between NASA and the NSF; between NASA and other U.S. government entities; between NASA and private sector organizations; between NASA and its international partners; and 9. The state of the profession including issues of diversity, inclusion, equity, and accessibility, the creation of safe workspaces, and recommended policies and practices to improve the state of the profession. Where possible, provide specific, actionable and practical recommendations to the agencies and community to address these areas. In response to this request, the National Academies’ established the Committee on the Planetary Science and Astrobiology Decadal Survey (hereafter, the “survey committee” or the “committee”) consisting of a 19-member steering group and 78 additional experts organized into six topical panels. The co-chairs of the survey committee were appointed in May 2020, and the members of the panels were identified and appointed in the subsequent spring and summer months. The steering group held its first meeting on September 30, 2020, and held its 22nd and final meeting on November 2, 2021. The six panels each held at least 20 meetings during the period October 2020 to September 2021. Notably, each and every single meeting was held virtually because of the ongoing COVID-19 pandemic. The work of the survey committee can be divided into three distinct phases, the last three months of 2020, the first 9 months of 2021, and late-Summer/early-Autumn of 2021. In phase one, the steering group deliberated on and defined the key science questions around which the report will be structured. In parallel, the panels ingested and assessed candidate missions already studied and identified additional concepts deemed worthy of study. Phase one ended with the development of two key items. First, a cross-survey consensus that the most appropriate key questions had been identified. Second, the prioritization by the steering group of 10 new mission concepts worthy of additional study. These 10 new concepts were subsequently forwarded to NASA for detailed study. To ensure that the panels would perform their initial task in an expeditious manner, they were organized and appointed so as to each have responsibility for different portions of the solar system—that is, Mercury and the Moon, Venus, Mars, giant planet systems, ocean worlds and dwarf planets, and small solar system bodies. During the second phase, the panels worked with mission-design teams at the Jet Propulsion Laboratory, NASA Goddard Space Flight Center, and at the Johns Hopkins University Applied Physics Laboratory to develop the 10 new mission concepts. In parallel, a series of approximately 20 informal, cross-survey writing groups—each consisting of five-to-ten members from the steering group and the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION x 

panels—were established to create the initial drafts of the chapters in this report devoted to the key science questions and to programmatic issues such as the state of the profession, research and analysis, and technology development. Once the additional mission studies were completed, their sponsoring panels performed a comparative assessment of the degree to which the new concepts and other proposed and studied missions could address the survey’s key science questions. This phase of the survey ended with the completion of the initial drafts of 20 of this report’s 23 chapters and the prioritization by the steering group of 17 mission concepts (some new and some old) for detailed technical risk and cost evaluation (TRACE) by the Aerospace Corporation. Phase three involved the scheduling of some 20 survey-wide “summit meetings,” during which the text produced by each writing group was subjected to intense comment, review, and subsequent revision. In parallel, the steering group assessed the results of the TRACE analyses, selected the most promising ones, prioritized them, and, thus, established the survey’s list of recommended mission activities for the coming decade. In addition, the steering group worked with the leaders of each writing group to integrate the draft text of the various chapters into a self-consistent and coherent program of activities for the next decade. The final task performed was the drafting by the steering group of the summary and the chapter describing the recommended program of activities for the period 2023-2032. Final sections of the report were drafted, assembled, and integrated in October and November 2021. The text was sent to external reviewers in December, was revised between January and February 2022, and was formally approved for release by the National Academies on March 24, 2022. The work of the committee was made easier thanks to the important help given by individuals too numerous to list—indeed, printing just the names of those individuals who made public presentations to the survey committee would require two full pages of text—at a variety of public and private organizations, who made presentations at committee meetings, drafted white papers, and participated in mission studies. Important contributions were also made by the TRACE team at The Aerospace Corporation, led by Russell Persinger, Justin Yoshida, and Mark Barrera. Finally, the survey committee thanks Kellie Mendelow for her invaluable record keeping, file management, and editorial assistance. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xi 

Acknowledgment of Reviewers This Consensus Study Report was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide candid and critical comments that will assist the National Academies of Sciences, Engineering, and Medicine in making each published report as sound as possible and to ensure that it meets the institutional standards for quality, objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We thank the following individuals for their review of this report: Irene Blair, University of Colorado, Mark Boslough, University of Arizona, John Chambers, Carnegie Institution for Science, Leroy Chiao, Independent Consultant, Gerhard Drolshagen, Carl von Ossietzky University of Oldenburg, Katherine H. Freeman, NAS, 1 Pennsylvania State University, B. Scott Gaudi, Ohio State University, Gerald F. Joyce, NAS/NAM, 2 Salk Institute for Biological Studies, Antonio Lazcano, National Autonomous University of Mexico, Mark S. Marley, University of Arizona, Timothy J. McCoy, National Museum of Natural History, Melissa A. McGrath, SETI Institute, Charles Norton, Jet Propulsion Laboratory, Louise M. Prockter, Applied Physics Laboratory, Joseph H. Rothenberg, Independent Consultant, Teresa Segura, Boeing Horizon X Ventures, Sean C. Solomon, NAS, Lahmont-Doherty Earth Observatory, David J. Stevenson, NAS, California Institute of Technology, Sarah T. Stewart, University of California, Davis, Grant H. Stokes, NAE, 3 MIT Lincoln Laboratory, Theresa A. Sullivan, University of Virginia, and Orenthal J. Tucker, NASA Goddard Space Flight Center. Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations of this report nor did they see the final draft before its release. The review of this report was overseen by Rosaly M. Lopes, Jet Propulsion Laboratory, and Norman H. Sleep, NAS, Stanford University. They were responsible for making certain that an independent examination of this report was carried out in accordance with the standards of the National Academies and that all review comments were carefully considered. Responsibility for the final content of the report rests entirely with the authoring committee and the National Academies. 1 Member, National Academy of Sciences. 2 Member, National Academy of Medicine. 3 Member, National Academy of Engineering. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xiii 

Contents SUMMARY S-1 1 INTRODUCTION TO PLANETARY SCIENCE, ASTROBIOLOGY, 1-1 AND PLANETARY DEFENSE Planetary Science and Astrobiology, 1-1 Planetary Defense, 1-4 The Relationship between Ground and Space-Based Research, 1-4 Support for Planetary Science and Astrobiology, 1-5 International Cooperation, 1-10 Planetary Science Decadal Surveys and Related Reports, 1-13 Scientific Scope of This Report, 1-15 A Guide to Reading This Report, 1-16 References, 1-17 2 TOUR OF THE SOLAR SYSTEM: A TRANSFORMATIVE DECADE OF EXPLORATION 2-1 Mercury, 2-1 The Moon, 2-7 Venus, 2-15 Mars, 2-24 Small Solar System Bodies, 2-35 Giant Planet Systems, 2-47 Ocean Worlds and Dwarf Planets, 2-57 3 PRIORITY SCIENCE QUESTIONS 3-1 4 QUESTION 1: EVOLUTION OF THE PROTOPLANETARY DISK 4-1 Q1.1 What Were the Initial Conditions in the Solar System? 4-2 Q1.2 How Did Distinct Reservoirs of Gas and Solids Form and Evolve in the Protoplanetary Disk? 4-8 Q1.3 What Processes Led to the Production of Planetary Building Blocks? 4-13 Q1.4 How and When Did the Nebula Disperse? 4-18 Supportive Activities for Question 1, 4-21 References, 4-21 5. QUESTION 2: ACCRETION IN THE OUTER SOLAR SYSTEM 5-1 Q2.1 How Did the Giant Planets Form? 5-1 Q2.2 What Controlled the Compositions of the Material that Formed the Giant Planets?, 5-7 Q2.3 How Did Satellites and Rings Form around the Giant Planets During the Accretion Era? 5-10 Q2.4 How Did the Giant Planets Gravitationally Interact with Each Other, the Protosolar Disk, and Smaller Bodies in the Outer Solar System? 5-15 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xv 

Q2.5 How Did Processes in the Early Outer Solar System Produce the Structure and Composition (Surface and Interior) of Pluto and the Trans-Neptunian Objects? 5-20 Q2.6 How Did the Orbital Structure of the Trans-Neptunian Belt, the Oort Cloud, and the Scattered Disk Originate, and How Did Gravitational Interactions in the Early Outer Solar System Lead to Scattering and Ejection? 5-24 Supportive Activities for Question 2, 5-28 References, 5-29 6 QUESTION 3: ORIGIN OF EARTH AND INNER SOLAR SYSTEM BODIES 6-1 Q3.1 How and When Did Asteroids and Inner Solar System Protoplanets Form? 6-1 Q3.2 Did Giant Planet Formation and Migration Shape the Formation of the Inner Solar System? 6-6 Q3.3 How Did the Earth-Moon System Form? 6-9 Q3.4 What Processes Yielded Mars, Venus, and Mercury and Their Varied Initial States? 6-11 Q3.5 How and When Did the Terrestrial Planets and Moon Differentiate? 6-14 Q3.6 What Established the Primordial Inventories of Volatile Elements and Compounds in the Inner Solar System? 6-19 Supportive Activities for Question 3, 6-25 References, 6-25 7 QUESTION 4: IMPACTS AND DYNAMICS 7-1 Q4.1 How Have Planetary Bodies Collisionally and Dynamically Evolved Throughout Solar System History? 7-1 Q4.2 How Did Impact Bombardment Vary with Time and Location in the Solar System? 7-7 Q4.3 How Did Collisions Affect the Geological, Geophysical, and Geochemical Evolution and Properties of Planetary Bodies? 7-14 Q4.4 How Do the Physics and Mechanics of Impacts Produce Disruption of and Cratering on Planetary Bodies? 7-20 Supportive Activities for Question 4, 7-22 References, 7-23 8 QUESTION 5: SOLID BODY INTERIORS AND SURFACES 8-1 Q5.1 How Diverse Are the Compositions and Internal Structures Within and Among Solid Bodies? 8-1 Q5.2 How Have the Interiors of Solid Bodies Evolved? 8-5 Q5.3 How Have Surface/Near-Surface Characteristics and Compositions of Solid Bodies Been Modified by, and Recorded, Interior Processes? 8-9 Q5.4 How Have Surface Characteristics and Compositions of Solid Bodies Been Modified by, and Recorded, Surface Processes and Atmospheric Interactions? 8-13 Q5.5 How Have Surface Characteristics and Compositions of Solid Bodies Been Modified by, and Recorded, External Processes? 8-16 Q5.6 What Drives Active Processes Occurring in the Interiors and on the Surfaces of Solid Bodies? 8-19 Supportive Activities for Question 5, 8-24 References, 8-24 9 QUESTION 6: SOLID BODY ATMOSPHERES, EXOSPHERES, MAGNETOSPHERES, 9-1 AND CLIMATE EVOLUTION Q6.1 How Do Solid-Body Atmospheres Form and What Was Their State During and Shortly after Accretion? 9-2 Q6.2 What Processes Govern the Evolution of Planetary Atmospheres and Climates PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xvi 

Over Geologic Timescales? 9-6 Q6.3 What Processes Drive the Dynamics and Energetics of Atmospheres on Solid Bodies? 9-9 Q6.4 How Do Planetary Surfaces and Interiors Influence and Interact with Their Host Atmospheres? 9-14 Q6.5 What Processes Govern Atmospheric Loss to Space? 9-19 Q6.6 What Chemical and Microphysical Processes Govern the Clouds, Hazes, 9-23 Chemistry and Trace Gas Composition of Solid Body Atmospheres? References, 9-27 10 QUESTION 7: GIANT PLANET STRUCTURE AND EVOLUTION 10-1 Q7.1 What Are Giant Planets Made of and How Can This Be Inferred from Their Observable Properties? 10-1 Q7.2 What Determines the Structure and Dynamics Deep Inside Giant Planets and How Does It Affect Their Evolution? 10-5 Q7.3 What Governs the Diversity of Giant Planet Climates, Circulation, and Meteorology? 10-9 Q7.4 What Processes Lead to the Dramatically Different Outcomes in the Structure, Content, and Dynamics of the Outer Planets’ Magnetospheres and Ionospheres? 10-12 Q7.5 How Are Giant Planets Influenced by, and How Do They Interact with, Their Environment? 10-16 Supportive Activities for Question 7, 10-17 References, 10-17 11 QUESTION 8: CIRCUMPLANETARY SYSTEMS 11-1 Q8.1 How Did Circumplanetary Systems Form and Evolve Over Time to Yield Different Planetary Systems? 11-2 Q8.2 How Do Tides and Other Endogenic Processes Shape Planetary Satellites? 11-6 Q8.3 What Exogenic Processes Modify the Surfaces of Bodies in Circumplanetary Systems? 11-12 Q8.4 How Do Planetary Magnetospheres Interact with Satellites with Rings, and Vice Versa? 11-15 Q8.5 How Do Rings Evolve and Coalesce into Moons? 11-18 Supportive Activities for Question 8, 11-21 References, 11-21 12 QUESTION 9: INSIGHTS FROM TERRESTRIAL LIFE 12-1 Q9.1 What Were the Conditions and Processes Conducive to the Origin and Early Evolution of Life on Earth, and What Do They Teach Us About the Possible Emergence and Evolution of Life on Other Worlds? 12-3 Q9.2 What Is the Diversity, Distribution, and Range of Possible Metabolic Strategies of Life in Terrestrial Environments (Surface, Subsurface, Atmosphere) and How Did They Evolve Through Time? 12-8 Q9.3 How Do Investigations of Earth’s Subsurface Environments Inform What Habitability and/or Life on Other Worlds Might Look Like? 12-12 Q9.4 How Can Our Knowledge of Life and Where and How It Arises and Is Sustained on Earth Illuminate the Search for Life Beyond Earth? 12-16 Q9.5 How Do Record Bias, Preservational Bias, False Negatives, and False Positives Play a Role in Biosignature Detectability and Reliability on Earth and What Are the Implications for Targets Beyond? 12-20 References, 12-23 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xvii 

13 QUESTION 10: DYNAMIC HABITABILITY 13-1 Q10.1 What Is “Habitability”? 13-1 Q10.2 Where Are or Were the Solar System’s Past or Present Habitable Environments? 13-4 Q10.3 Water Availability: What Controls the Amount of Available Water on a Body Over Time? 13-9 Q10.4 Organic Synthesis and Cycling: Where and How Are Organic Building Blocks of Life Synthesized in the Solar System? 13-13 Q10.5 What Is the Availability of Nutrients and Other Inorganic Ingredients to Support Life? 13-17 Q10.6 What Controls the Energy Available for Life? 13-20 Q10.7 What Controls the Continuity or Sustainability of Habitability? 13-23 Supportive Activities for Question 10, 13-25 References, 13-25 14 QUESTION 11: SEARCH FOR LIFE ELSEWHERE 14-1 Q11.1 Path to Biogenesis: What Is the Extent and History of Organic Chemical Evolution, Potentially Leading Toward Life, in Habitable Environments Throughout the Solar System? How Does This Inform the Likelihood of False Positive Life Detections? 14-3 Q11.2 Biosignature Potential: What Is the Biosignature Potential in Habitable Environments Beyond Earth? What Are the Possible Sources of False Positives and False Negatives? 14-7 Q11.3 Life Detection: Is or Was There Life Elsewhere in the Solar System? 14-11 Q11.4 Life Characterization: What Is the Nature of Life Elsewhere, If It Exists? 14-16 References, 14-20 15 QUESTION 12: EXOPLANETS 15-1 Q12.1 Evolution of the Protoplanetary Disk, 15-3 Q12.2 Accretion in the Outer Solar System, 15-5 Q12.3 Origin of Earth and Inner Solar System Bodies, 15-6 Q12.4 Impacts and Dynamics, 15-8 Q12.5 Solid Body Interiors and Surfaces, 15-9 Q12.6 Atmosphere and Climate Evolution on Solid Bodies, 15-11 Q12.7 Giant Planet Structure and Evolution, 15-14 Q12.8 Circumplanetary Systems, 15-15 Q12.9 Insights from Terrestrial Life, 15-16 Q12.10 Dynamic Habitability, 15-19 Q12.11 Search for Life Elsewhere, 15-21 Supportive Activities for Question 12, 15-22 References, 15-23 16 STATE OF THE PROFESSION 16-1 Introduction, 16-1 Implicit and Systemic Bias, 16-2 The Evidence, 16-4 White Papers Submitted to the Survey, 16-13 Summary of Findings, 16-14 Recommendations, 16-24 References, 16-28 17 RESEARCH AND ANALYSIS 17-1 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xviii 

What Is R&A? 17-4 The Internal Scientist Funding Model, 17-5 The Role of Virtual Institutes and Research Coordination Networks, 17-7 Is the R&A Portfolio Optimized for NASA’s Scientific Needs? 17-9 R&A Proposal Review Process, 17-13 Trends in PSD R&A Funding and Programs through Time, 17-17 Recommended Funding for NASA Planetary R&A, 17-22 The Appropriate Size of the Planetary Research Community, 17-25 NASA-NSF Partnerships, 17-28 References, 17-29 18 PLANETARY DEFENSE: DEFENDING EARTH THROUGH 18-1 APPLIED PLANETARY SCIENCE NEO Detection, Tracking, and Characterization, 18-5 NEO Modeling, Prediction, and Information Integration, 18-14 NEO Deflection and Disruption Missions, 18-19 International Cooperation on NEO Preparation, 18-27 NEO Impact Emergency Procedures and Action Protocols, 18-28 Conclusions, 18-28 References, 18-29 19 HUMAN EXPLORATION 19-1 The Pivotal Role of Science in Human Exploration, 19-1 Science Enabled by Human Explorers, 19-2 Near-Term Human Exploration Plans, Relationship to Science, and In Situ Resource Utilization, 19-4 Integrating Science into Human Exploration, 19-6 NASA Programmatic Considerations for Artemis and Beyond: Challenges of Integrating Science and Human Exploration, 19-6 Scientific and Human Exploration of Mars, 19-11 A Tale of Two Orbiters: LRO and IMIM, 19-13 Research Programs to Enable and Optimize Human Exploration, 19-14 Role of Commercial Space and Human-Scale Vehicle Capabilities, 19-15 External Cooperation, 19-17 References, 19-18 20 INFRASTRUCTURE FOR PLANETARY SCIENCE AND EXPLORATION 20-1 NASA Infrastructure, 20-1 Supporting NSF Infrastructure, 20-12 Intra-Agency, Interagency, and International Collaborations, 20-15 References, 20-16 21 TECHNOLOGY 21-1 Technology Development in NASA, 21-2 Technologies for this Decade and Beyond, 21-8 Instrumentation, 21-11 General Technology Areas, 21-13 Disruptive and Game-Changing Trends in Technologies, 21-25 References, 21-28 22 RECOMMENDED PROGRAM: 2023-2032 22-1 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xix 

Scientific Themes and Priority Science Questions, 22-1 Ongoing Missions and Existing Programs, 22-5 Discovery, New Frontiers, and Flagship Recommendations for the Decade 2023-2032, 22-20 Representative Flight Programs for the Decade, 22-36 State of the Profession, 22-42 Other Key Programmatic Recommendations, 22-42 23 THE FUTURE 23-1 Continuing Oversight, 23-1 The Midterm Review, 23-2 Preparing for the Next Decadal Survey, 23-2 References, 23-3 APPENDIXES A Letter of Request, Statement of Task, and Other Guidance A-1 B White Papers Received B-1 C Technical Risk and Cost Evaluation of Priority Missions C-1 D Missions Studied but not Sent for TRACE D-1 E Panel Missions Not Selected for Additional Study E-1 F Glossary and Acronyms F-1 G Biographies of Committee Members and Staff G-1 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION xx