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

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1 Introduction to Planetary Science, Astrobiology, and Planetary Defense In spring 2011, when the last planetary decadal survey Vision and Voyages for Planetary Science in the Decade 2013-2022 was released, the New Horizons spacecraft was speeding toward Pluto, Europe’s Rosetta was heading toward a rendezvous with a comet, Cassini was still orbiting Saturn, and the GRAIL, Curiosity, OSIRIS-REx, and Juno missions had not yet launched (see Figures 1.1 through 1.4). Since that time, these spacecraft and others have completed their primary missions and dramatically expanded our understanding of the solar system. They have studied the atmosphere and interior of Jupiter, the interior of Saturn, the water plumes of Enceladus, the topography and geochemistry of Pluto and its moon Charon, the seismology and habitability of Mars, the surface of the asteroid Bennu, and the icy chemistry of a comet. They have contributed to planetary science and astrobiology in tremendous ways. The intent of this chapter is to provide general background for the non-technical reader wishing to know something more about planetary science, astrobiology and planetary defense. “Planetary science” is the shorthand definition for an array of scientific disciplines that collectively seek to answer questions about how the solar system formed, what initial conditions and subsequent processes shape how planetary bodies evolve and interact with each other and the environment, and how these factors enabled the conditions for life to form on at least one planet in the solar system. The latter feeds into the growing field of “astrobiology”, the study of the origin and evolution of life on planetary bodies. These activities are tightly interlinked, and both have advanced substantially in the decade since Vision and Voyages (NRC 2011). Further advances are dependent not only upon new space missions to study the solar system, but also on basic research to understand the scientific data and to formulate new hypotheses, as well as on technology development to enable future mission and experimental studies. PLANETARY SCIENCE AND ASTROBIOLOGY Planetary science is a multidisciplinary activity involving members of the geology, geophysics, geochemistry, astronomy, atmospheric science, and space physics communities. These communities study planetary bodies as well as Earth. Astrobiology is, at its most basic, the study of the origin, evolution, and distribution of life in the universe (NASEM 2018b). Astrobiology was recognized as an organized scientific discipline more recently than planetary science and is inherently even more multidisciplinary, encompassing biology, aspects of heliophysics (often referred to as solar and space physics), planetary science, and astronomy. Astrobiology includes laboratory activities as well as field studies in terrestrial surface and marine environments, theoretical work, and sample analyses. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-1 

FIGURE 1.1 The descent stage for Mars 2020 hovers as the Perseverance rover is lowered to the martian surface in 2021. SOURCE: NASA. FIGURE 1.2 An artist’s impression of the Juno spacecraft at Jupiter. Juno is currently studying Jupiter’s interior, composition, and atmosphere. SOURCE: NASA. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-2 

FIGURE 1.3 The InSight spacecraft during final assembly. InSight has provided data on the internal structure of Mars via seismology. SOURCE: NASA. FIGURE 1.4 The New Horizons spacecraft during final integration in 2005. New Horizons flew past Pluto and its large moon Charon in 2015, and then past 486958 Arrokoth, a Kuiper belt object, in 2019. SOURCE: NASA. The search for life in the solar system and beyond has been a focus of many current and future spaceflight missions conducted by NASA and other space agencies. A new concept of dynamic habitability has emerged in recent decades that views habitability—the ability of a specific planetary environment to support life—as a continuum. An environment may transition from inhabitable to uninhabitable over time, a function of planetary and environmental evolution. Astrobiology and planetary science take an integrated, systems-level view of the origin and evolution of planetary bodies, seeking to understand how life and its environment may have changed together or co-evolved. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-3 

PLANETARY DEFENSE Planetary defense is an international cooperative effort to detect and track objects that could pose a threat to life on Earth. As such it motivations are more concerned with human health and safety rather than the advancement of scientific understanding. The threat posed by extraterrestrial bodies to Earth and its inhabitants was amply demonstrated in 2013, when a 20-m diameter asteroid detonated at an altitude of some 23 km over the Siberian city of Chelyabinsk.The resulting explosion released nearly 450 kt (~2 petajoules) of energy and caused non-fatally injuring to more than 1,600 people. This event highlighted the fact that Earth travels around the Sun amidst millions of small objects in similar orbits that sometimes cross Earth’s orbit (see, for example, NASEM 2018c). Planetary science and exploration provide knowledge and tools to detect, track, and characterize such objects, key inputs to developing realistic detection and mitigation strategies against these natural disasters. Starting in the 1990s, Congress and presidential administrations have directed NASA to take a lead role in planetary defense and that role has grown in the past decade. NASA, NSF, and other government agencies collaborate in activities in support of planetary defense. 1 This decadal survey is the first to include planetary defense in its charter. THE RELATIONSHIP BETWEEN GROUND AND SPACE-BASED RESEARCH Planetary science is a multidisciplinary endeavor and is conducted by a synergistic combination of ground- and space-based activities. No one type of research approach (e.g., spacecraft missions, telescopic observation, and theoretical studies) is more or less important that the others. All research approaches and techniques have a role to play if progress is to be made in addressing key scientific issues. The first planetary scientists explored the solar system from the ground, using increasingly powerful telescopes to first discover and then study the planets. Mercury, Venus, Mars, Jupiter and Saturn were all visible in the night sky with the naked eye. The Galilean satellites were discovered by Galileo Galilei in 1610, Uranus was discovered by William Herschel in 1781, Neptune by Johann Galle and Urbain Le Verrier in 1846, and Pluto by Clyde Tombaugh in 1930. Even as the United States and Soviet Union began sending spacecraft to the Moon and then to Mars and Venus starting in the late 1950s, ground-based astronomy played an important role in understanding the solar system, such as by analyzing radio signals from Jupiter or conducting radar observations of Mercury, Venus, and asteroids. Today, ground and space-based telescopic observations continue to provide key support to robotic space missions, e.g., by characterizing targets in advance of spacecraft encounters, and ongoing observations provide data between missions as well. Many ground-based telescopes used in planetary science research are supported by the National Science Foundation (NSF), although specific research funding to use them may come from NASA or other sources. Spacecraft and telescopic observations are not the only means researchers use to study planetary bodies. Significant amounts of work are undertaken in laboratories and by field studies in relevant terrestrial and marine environments. Data analysis, and theoretical and computational modelling also play fundamental roles. Moreover, the work of a relatively small number of planetary scientists and astrobiologists worldwide would go for naught without the backup and support of a far greater number of engineers, technicians, program managers, and administrators in agencies, organizations, and private companies who keep the space-science enterprise viable. 1 Although assets maintained for national security purposes by the newly established U.S. Space Force are relevant to the detection and tracking of objects in near-Earth space that might pose a hazard, planetary defense is not currently included in its mission statement. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-4 

SUPPORT FOR PLANETARY SCIENCE AND ASTROBIOLOGY The principal federal organizations that support the nation’s programs in planetary science are the Planetary Science Division (PSD) of NASA’s Science Mission Directorate, and the Division of Astronomical Sciences (AST) in NSF’s Directorate for Mathematical and Physical Sciences Division. Other federal departments, agencies, and organizations provide important financial and other support for aspects of planetary science and astrobiology. The Department of Energy’s (DOE’s) national laboratories, for example, support groups whose primary roles are areas such as nuclear forensics and shock physics. Such groups have important secondary roles in the geochemical analysis of extraterrestrial materials and the modelling of asteroid impacts, respectively. DoE’s National Nuclear Secutity Administration, through its Stewardship Science Academic Alliances supports work relevant to the behavior of matter under the conditions found in the interiors of planetary bodies at its Capital/DOE Alliance Center and the Center for Matter under Extreme Conditions. Similarly, the massive gene-sequencing and computational capabilities of DoE’s Genomic Science Program are directly relevant to aspects of astrobiology. Also, of relevance to astrobiology are a subset of activities supported by the National Institutes of Health (NIH). Examples include the support of individual researchers investigating the chemical and physical processes that facilitated the transition from chemical evolution to biological evolution on the early Earth. Private research and philanthropic entities are also involved in supporting various aspects of planetary science and astrobiology, but their contributions are beyond the scope of this report. The remainder of this section is devoted to a more detailed look at activities underway at NASA and NSF. The primary goals of NASA’s PSD are to ascertain the origin and history of the solar system, to understand the potential for life beyond Earth, and to characterize hazards and resources present as humans explore space. Spacecraft missions, technology development, research infrastructure, and basic research and analysis programs are supported by PSD to advance these goals. The majority of PSD’s budget is devoted to the development, construction, launch, and operation of robotic spacecraft. PSD conducts large strategic (so-called flagship) missions and smaller Discovery and New Frontiers missions that are proposed and led by principal investigators (PIs). Examples of past and current flagship missions include Cassini, the Curiosity and Perseverance rovers, and Europa Clipper (Figure 1.5); examples of New Frontiers missions include New Horizons, Juno, and OSIRIS-REx (Figure 1.6). The primary purpose of NSF-AST is to support research in ground-based optical, infrared, and radio astronomy. NSF-AST provides access to world-class research facilities and supports the development of new instrumentation and next-generation facilities. NSF-AST also supports basic research in planetary astronomy. However, NSF-AST does not, in general, support activities that are also funded by NASA: e.g., the analysis of data returned by planetary spacecraft missions. Relevant Activities in Other NASA Divisions and Directorates Planetary science activities at NASA are strongly coupled to the agency’s other science programs in the Astrophysics, Heliophysics, and to a more limited extent, Earth Science and Biological and Physical Science divisions. Similarly, activities underway in other NASA’s directorates are of direct relevance to planetary science and astrobiology. Each is addressed below. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-5 

FIGURE 1.5 Artist conception of the Cassini spacecraft during its final plunge into Saturn’s atmosphere in 2017. SOURCE: NASA/JPL. FIGURE 1.6 OSIRIS-REx’s sampling arm in the process of collecting material from the surface of the asteroid 101955 Bennu in 2020. SOURCE: NASA. Astrophysics Division The major science goals of the Astrophysics Division (APD) are to discover how the universe works, explore how the universe began and evolved, and to search for planetary environments that may hold keys to life’s origins or even might themselves sustain life. APD assets such as the Hubble Space Telescope have PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-6 

played major roles in advancing planetary science through the study of solar system bodies such as, e.g., the atmospheres of the outer planets. Hubble also was used to study the vicinity of Pluto to plan for New Horizons’ 2015 flyby and to identify possible future target for the spacecraft to study. The James Webb Space Telescope is expected to make substantial contributions to planetary science. Another key area where the interests of APD and PSD overlap is in the study of extrasolar planetary systems (see, for example, NASEM 2018c). Heliophysics Division NASA’s Heliophysics Division sponsors research in solar and space physics, with particular emphasis on understanding the Sun and its interactions with Earth and other bodies in the solar system. This research also includes study of the particle and field environments of other solar system bodies and includes comparative studies of planetary magnetospheres, ionospheres, and upper atmospheres. Spacecraft such as the Voyagers are taking measurements at the distant edges of the Sun’s influence and the beginning of the interstellar medium. Earth Science Division NASA’s Earth Science Division (ESD) also has important connections to the study of planetary science. The major scientific goal of this division is to advance Earth system science to meet the challenges of climate and environmental change. A better understanding of Earth provides data that enables understanding of the origin and evolution of a terrestrial planetary biosphere. A common interest of both astrobiologists and Earth scientists is how biospheres interact with their host planetary environments. However, the domains of interest to the two communities are somewhat dissimilar. Astrobiologists are mostly interested in the impact of interactions over geological timescales (~100 million to a billion years), whereas Earth science is most interested in changes over much shorter times (~1 to a million years). The science, technologies, and observational techniques developed for remote sensing of Earth help inform planetary science and astrobiology. However, planetary spacecraft operate in more difficult environments than Earth-orbiting spacecraft and have different design requirements and mass and power limitations, meaning that Earth observation instruments are not typically directly applicable to planetary science needs. Biological and Physical Science Division NASA’s Biological and Physical Science Division (BPSD) was recently incorporated into the Science Mission Directorate. Much of BPSD’s research pertains to how microgravity and partial gravity environments affect contemporary biological processes (e.g., adaption of organisms to the space environment and the health and safety of astronauts). BPS is also interested in the response of physical systems to low-gravity environments. Familiar and well understood processes—e.g., fluid flow through pipes, combustion, and material effects such as the formation of alloys—behave in a fundamentally different manner when gravitational effects are reduced or eliminated. While BPS has limited overlap with planetary science and astrobiology, some aspects of biological and physical research are directly relevant to future activities such as the in situ utilization of planetary resources—e.g., extraction of oxygen from the martian atmosphere or ice mining on the Moon—or the creation of long-lived, life-support systems. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-7 

Space Technology Mission Directorate NASA’s Space Technology Mission Directorate develops a wide range of technologies to support agency needs in the mid- to long-term. Some of these technologies, such as communications and in-space propulsion, are of significant value to planetary science missions. Technologies that are more specific to the near-term needs of planetary science and astrobiology, such as spacecraft instrumentation, are supported directly by PSD. Exploration Systems Development Mission Directorate In September 2021, as this report was being written, NASA established the Exploration Systems Development Mission Directorate (ESDMD) to oversee the Artemis program to send humans to the Moon. In particular, ESDMD is responsible for developing systems to support human operations on the Moon. PSD collaborates with ESDMD to develop precursor lunar robotic missions and to define those scientific activities that astronauts will conduct on the Moon and, eventually, Mars. A current major area of collaboration between these two parts of NASA is in the development of the Volatiles Investigating Polar Exploration Rover, currently scheduled to land in the Nobile region near the Moon’s South Pole in late- 2023. Relevant Activities in Other NSF Divisions and Directorates As already mentioned, the principal source of planetary science funding within NSF is in its Division of Astronomical Sciences. However, other parts of NSF, particularly activities within the Directorate for Geosciences, make important contributions to planetary science and astrobiology. However, much of these planetary science activities are concerned with the focused studies of the Earth system and, as such, are beyond the scope of this study (see Appendix A, Scope, item 4). Nevertheless, a small subset of activities finded by the Directorate for Geosciences (e.g., geochemical and cosmochemical of terrestrial and extraterrestrial materials) are very important to the planetary science communities. Similarly, other federal agencies and organizations provide niche support for small subsets of the planetary science and astrobiology communities. While these activities do not support a significant number of planetary scientists or astrobiologists, they are important because they maintain key linkages between space scientists and the very much larger community of researchers studying aspects of, for example, the Earth system, matter under conditions of extreme temperatures and pressures, and fundamental biology. Such linkages provide important means for cross-fertilizing ideas, concepts, and breakthroughs between what might seem disparate research communities. Subsequent sections highlight the important work supported by some of NSF’s divisions and directorates. Office of Polar Programs The Office of Polar Programs (OPP) provides access to and logistical support for researchers working in Antarctica. One of the key U.S. activities in the southern polar region is the Antarctic Search for Meteorites Program. Initiated in 1975 and run as a cooperative activity involving OPP, NASA, and the Smithsonian Institution. The meteorites collected in Antarctica have provided insights into many planetary bodies, including the Moon and Mars. The Smithsonian’s National Museum of Natural History is responsible for initial examination and characterization of meteorites collected in Antarctica. The Astromaterials Acquisition and Curation Office at NASA’s Johnson Space Center is responsible for long- term curation and distribution of samples to the research community. Antarctic research is also relevant to other aspects of planetary science and astrobiology. Important examples of OPP activities include support PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-8 

for the study of sub-glacial lakes and Mars-analog environments in the Dry Valleys. The former are terrestrial analogs to the oceans known to exist beneath the icy surfaces of objects such as Enceladus (see Figure 1.7). OPP activities have been severely impacted by the COVID-19 pandemic, with most, if not all, activities planned for the 2020-2021 and 2021-2022 field seasons cancelled. Division of Atmospheric and Geospace Sciences This part of NSF supports fundamental research regarding physical, chemical, and biological processes that impact the composition and physical phenomena and behavior of matter between the Sun and the surface of Earth. Important areas of research synergies with planetary science include the development of atmospheric and general circulation models for other planets and comparative studies of the plasma process Division of Earth Sciences Research in this division focusses on understanding the structure, composition, and evolution of Earth, the life it supports, and the physical and chemical process governing the formation and behavior of minerals, rocks, and other materials. One area of this division’s interest is directly relevant to the study of extraterrestrial materials. The geochemical techniques developed to understand the formation and behavior of terrestrial rocks and minerals are directly applicable to the analysis and study of meteorites, cosmic dust, and samples return to Earth from other solar system bodies. FIGURE 1.7 An artist’s impression of the Cassini spacecraft against the backdrop of the ice plumes of Enceladus. The presence of liquid water below Enceladus’ icy surface is of particular interest to astrobiologists. Laboratory studies as well as field activities to study the permanently ice-covered lakes in Antarctica inform the study of icy bodies such as Enceladus and Europa. SOURCE: NASA Division of Ocean Sciences This part of NSF is responsible for research, infrastructure, and educational activities designed to improve knowledge and understanding of Earth’s oceans and oceanic basins and their interactions with the integrated Earth system. Access to research ships, deep-diving submersibles, and core samples from oceanic drilling programs not only inform understanding of the structure and evolution of Earth and its biosphere PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-9 

but also provide a much-needed context for studies of other planetary environments. A particularly relevant example involves contributions to astrobiology made by studies of hot and cold deep-sea vents and their associated biospheres. Most telling is that life found in such systems employs a food-chain whose base is driven by chemical reactions at, for example, water-mineral interfaces and not by solar energy. As such, these marine biospheres may be directly analogous to ones possibly operating in the sub-surface oceans known to exist in the outer solar system. Division of Physics Another part of NSF playing an important supporting role in planetary science activities is the Division of Physics. An activity most worthy of mention here is support for theoretical, modelling, and experimental studies of the behavior of matter at the temperatures and pressures found in the interions of planetary bodies. For example, NSF’s Physics Frontiers Center for Matter at Atomic Pressures is largely motivated by major planetary science problems concerning the study the physical properties of matter at extreme pressures. Other NSF Programs Niche support for planetary science and astrobiology is also provided by other parts of NSF. While many of these activities are of limited scope and/or duration, they foster interdisciplinary research by bringing together researcher who would not normally interact with each other. A notable recent example was the so-called Ideas Lab on the origin of life, sponsored by NSF’s Biological Sciences and Geosciences directorates and NASA’s Astrobiology Program. Ideas Labs consist of a series of intensive workshops, whose participants are selected via a competitive process, designed to find innovative approaches to the study of major science questions. The near-term goal of this specific Ideas Lab was to develop a theoretical framework for events transpiring on the early Earth that encompasses the rival metabolism-first vs. RNA- first theories for the origin of life. INTERNATIONAL COOPERATION Planetary exploration is an increasingly international endeavor, with the United States, Russia, Japan, Canada, China, India, Israel, United Arab Emirates, and many European nations independently or collaboratively mounting major planetary missions. As budgets for space programs come under increasing pressure and the complexity of the missions grows, international cooperation becomes an enabling component. New alliances and mechanisms to cooperate are emerging, enabling partners to improve national capabilities, share costs, build common interests, and eliminate duplication of effort. NASA’s planetary science and astrobiology programs may have prompted other nations, large and small, to undertake similar activities. But that is not all. NASA is an extraordinary soft-power asset in that the results from its missions have changed the scope of courses and textbooks used in schools, colleges, and universities around the world. Moreover, NASA’s images of extraterrestrial objects are now commonplace in the national and international media. The extraordinary success of space missions is such that many graduate students and young scientists are willing to bet their careers on the results that can be obtained from space exploration. The soft-power aspects of NASA’s activities aside, international agreements and plans for cooperation need to be crafted with care, for they also can carry risks. The establishment of the NASA Astrobiology Institute (NAI), for example, prompted the establishment of similar organizations in other nations. However, the demise of NAI left many these non-US organizations in limbo because their specific relationship with NASA activities became unclear. The management of international spacecraft missions PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-10 

adds layers of complexity to their technical specification, management, and implementation. Different space agencies use different planning horizons, funding approaches, selection processes, and data dissemination policies. Informed estimates of cost (e.g., the TRACE process described in Appendix C) need not be a ‘show-stopper’ for international collaborations. But attempting to get good estimates of mission costs when there is significant international sharing of costs raises a number of complications. In some cases, for example, when an instrument is flown on a foreign spacecraft instead of being a NASA free- flyer, costs may be low enough that it does not meet the threshold for independent costing in a decadal survey. With the emergence of a new and highly entrepreneurial, commercial space sector in the U.S., NASA is fundamentally changing the traditional landscape for implementing space missions. However, such pioneering efforts as NASA’s Commercial Lunar Payload Services program have not yet been fully adopted by other countries. Such activities bring new players and stakeholders into the equation and may, potentially complicate activities between NASA and other national and international space agencies. For example, a foreign space agency willing to enter into a government-to-government partnership might be less sanguine about a three-way partnership with NASA and a commercial entity. Nonetheless, international cooperation remains a crucial element of the planetary program; it may be the only realistic option to undertake some of the most ambitious and scientifically rewarding missions. Advance planning through bilateral (or multilateral) agency discussions, scientific community involvement (via workshops and congresses, for example), and informed cost estimates and sharing of tasks is the most effective way to reap the benefits of such collaborations. Mechanisms and Recent Examples of Cooperation Flagship missions afford the greatest potential for NASA and other space agencies to unite resources to meet difficult challenges. The joint NASA-ESA (European Space Agency) Cassini-Huygens mission to explore the saturnian systems was a superb example of international cooperation (Figures 1.5 and 1.7). Large strategic missions like Cassini are complex to manage and implement as they involve integrating major spacecraft components supplied by different nations (engines, antennas, probes, dual spacecraft) into a single flight system. Still, to minimize the high fractional costs of launch and orbital insertion or landing, this architecture can be the most cost-effective one overall. The Cassini-Huygens mission was composed of two elements separately developed by NASA and ESA and delivered to the saturnian system by the same spacecraft. Such a separation of tasks/responsibilities has proven very effective and successful in the past and will also be beneficial in the future. Indeed, NASA and ESA have been considering undertaking joint missions of this integrated form, such as in the joint Europa Jupiter System Mission (EJSM) and Titan Saturn System Mission (TSSM) concept studies in the late 2020s, that failed to materialize in the end due to cost issues. Common collaborative arrangements range in scale from data-sharing arrangements to the provision of resources to foreign partners by NASA. These resources might include, for example, instruments, other key flight elements, and/or science-team members. NASA contributions to foreign missions have been funded by a variety of competitive programs such as the past “Mission of Opportunity” or the present SALMON (Stand-Alone Missions of Opportunity). Examples of foreign missions incorporating NASA-provided instruments include the following: India’s Chandrayaan-1 lunar orbiter; ESA’s BepiColombo Mercury and JUICE Ganymede orbiters; and Japan’s Hayabusa 1 and 2 asteroid sample return missions and the forthcoming Mars Moons Exploration spacecraft, designed to return samples from the martian moon Phobos in the late-2020s. International cooperation is a two-way street. NASA has contributed instruments, other items of hardware, and has provided communications and navigational support to a variety of non-U.S. missions. Examples include the following: Lunar Reconnaissance Orbiter includes a Russian instrument; the Juno Jupiter orbiter carries an Italian auroral experiment; the Mars Exploration Rovers and Phoenix lander included instruments and team members from Germany, Denmark, and Canada; and Russia, Canada; and PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-11 

various European nations contributed elements of the Curiosity and Perseverance Mars rovers.These collaborations dramatically expand mission capabilities and are crucial to developing a strong and effective national and international scientific community. Guidelines for International Cooperation Notwithstanding the enormous benefits, both societal and scientific, that international cooperation affords, such agreements are not necessarily of mutual benefit. As such, cooperative ventures require due consideration of all the pluses and minuses. Complicating aspects of cooperative ventures include the following: different goals for the endeavor, misaligned fiscal timelines and commitment schedules; use of mismatched proposal requirements and selection processes; miss-matched technical specifications, management by multiple, sometimes competing interests; agreement on implementation and integration procedures; and the impact of the International Trafficking in Arms Regulations. The time and effort to resolve these and other issues can lead to cost and schedule growth. As NASA pursues opportunities for collaboration with foreign partners, it needs to do so with full understanding of the potential risks and how they can be managed. Clearly articulated and readily understood cooperation guidelines are essential. As a result, the survey committee endorses, as a starting point, the following general principles and guidelines laid out in the joint report of the Space Studies Board and the European Space Science Committee entitled U.S.-European Collaboration in Space Science (NRC 1998): 1. Support through peer review that affirms the scientific integrity, value, requirements, and benefits of a cooperative mission; 2. Historical foundation built on an existing international community, partnership, and shared scientific experiences; 3. Shared objectives that incorporate the interests of scientists, engineers, and managers in common and communicated goals; 4. Clearly define responsibilities and roles for cooperative partners, including scientists, engineers, mission managers; 5. Agreed-upon processes for data calibration, validation, access, and distribution; 6. Establish a sense of partnership recognizing the unique contributions of each participant; 7. Beneficial characteristics of cooperation; and 8. Reviews for cooperative activities in the conceptual, developmental, active, or extended mission phases—particularly for foreseen and upcoming large-class spacecraft missions. Despite the negative consequences that may potentially accrue if cooperative activities are not planned and conducted in a manner consistent with the principles listed above, the committee strongly supports international efforts and encourages the expansion of international cooperation on planetary missions to accelerate technology maturation and share costs. From experience in the past decades, it appears that international cooperation generally provides resilience to long-term space programs and allows optimal use of an international workforce and expertise. Multiple international space powers (both traditional national space agencies and the private sector) have now mastered major technological challenges required to explore the solar system. As such, international cooperation will remain a key element of the nation’s planetary exploration program. An internationally engaged program of solar system exploration can unite stakeholders worldwide and lay the roadmap for humans to venture into space in the next phases of exploration. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-12 

PLANETARY SCIENCE DECADAL SURVEYS AND RELATED REPORTS In the 1970s and 1980s, science strategies for exploring the solar system were drafted by the National Research Council’s (NRC’s) Committee on Planetary and Lunar Exploration (COMPLEX), which addressed separately the inner planets, the outer planets, and primitive/small bodies. 2 In the early 1990s, COMPLEX crafted a single solar system strategy that united and updated the several preexisting documents, resulting in the report An Integrated Strategy for the Planetary Sciences: 1995-2010 (NRC 1994). In 2001, the NRC undertook the first planetary science decadal survey. This produced the 2002 report New Frontiers in the Solar System: An Integrated Exploration Strategy (NRC 2002). That report outlined science priorities and identified new initiatives needed to address the scientific priorities established in the decadal survey. The study advocated the creation of a new class of medium-sized missions, named New Frontiers. New Horizons was the first New Frontiers mission, launched in 2006. In 2010 the NRC undertook the second planetary science decadal survey which resulted in the spring 2011 delivery of the report Vision and Voyages for Planetary Science in the Decade 2013-2022. The 2011 decadal survey’s statement of task from NASA called for prioritized missions binned in small, medium and large categories with respective costs of less than $325 million, less than $650 million, and more than $650 million in then-year dollars 3. In addition, NASA was congressionally mandated to ask the decadal surveys to conduct an independent cost estimation process. In the 2011 decadal survey this was referred to as the Cost and Technical Estimation (CATE) process. In 2020, the name of the CATE process was changed to Technical Risk and Cost Estimation (TRACE) to emphasize the importance of technical risk assessment. Vision and Voyages produced a range of recommendations across the entire planetary science field, including for research and analysis and technology spending. It also included a set of priority mission recommendations that are summarized in Table 1.1. In addition to the decadal surveys, the National Academies has also undertaken mid-decade reviews of NASA’s planetary science and astrobiology programs. In 2018, the National Academies produced Visions into Voyages for Planetary Science in the Decade 2013-2022—A Midterm Review (NASEM 2018a). The report concluded that NASA had made substantial progress accomplishing the goals of the decadal survey and recommended additional actions leading to the current decadal survey. As an example, NASA designed, built, launched, and landed the Perseverance rover on Mars, a direct result of the 2011 decadal survey’s recommendations. (See Figure 1.8) 2 The National Research Council is the operating arm of the National Academies of Sciences, Engineering, and Medicine. Until 2017, the NRC name appeared on all National Academies reports. The name of the National Academies of Sciences, Engineering, and Medicine now appears on the covers of reports. 3 Then-year dollars being those including the effects of inflation and/or reflect the price levels prevailing during the year at issue. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-13 

TABLE 1.1 Priority Mission Recommendations for 2013-2022 from the Vision and Voyages Decadal Survey Vision and Voyages Priority and Disposition Prior to Current Status Recommendation Mission Type This Decadal Survey Mars Astrobiology Explorer- First priority Implemented by NASA Currently collecting and Cacher Large strategic mission as Mars caching samples for 2020/Perseverance return to Earth Jupiter Europa Orbiter Second priority Implemented by NASA Currently under Large strategic mission as Europa Clipper construction for launch in 2024 Uranus Orbiter and Probe Third priority NASA initiated a science n/a Large strategic mission definition team to examine Uranus and Neptune orbiter. Neptune Orbiter study undertaken via PMCS process Enceladus Orbiter Joint fourth priority Not implemented. n/a Large strategic mission Enceladus orbiter/lander study undertaken via the PMCS process Venus Climate Orbiter Joint fourth priority Not implemented. Venus n/a Large strategic mission Flagship mission study undertaken via the PMCS process New Frontiers Program First priority New Frontiers-4, Dragonfly to launch in A line of medium- Dragonfly, selected in 2027 class, PI-led missions. 2019 NF-5 announcement of At least two to be opportunity to be selected each decade released in 2024 and launched in the early 2030s Discovery Program First priority Lucy and Psyche selected Lucy launched in 2021 A line of small-class, in 2017; Psyche to launch in 2022 PI-led missions. At DAVINCI and DAVINCI and least five to be selected VERITAS selected in VERITAS under each decade 2021. development for launch in late-2020s. Next announcement of opportunity scheduled for late 2022 to 2023 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-14 

FIGURE 1.8 The Perseverance rover on Mars. This mission is collecting samples for later return to Earth. SOURCE: NASA. SCIENTIFIC SCOPE OF THIS REPORT The scientific scope of this report spans two dimensions: first, the principal scientific disciplines that collectively encompass the ground- and space-based elements of planetary science and astrobiology: i.e., planetary astronomy, geology, geophysics, atmospheric science, magnetohydrodynamics, celestial mechanics, and relevant aspects of the life sciences; and second, the physical territory within the committee’s purview; the solar system’s principal constituents and extrasolar planetary systems. This territory includes the following: • The major rocky bodies in the inner solar system: i.e., Mercury, Venus, the Earth-Moon, and Mars. • The giant planets in the outer solar system—i.e., Jupiter, Saturn, Uranus, and Neptune—including their magnetospheres; • The rings and satellites of the giant planets; • Dwarf planets in the asteroid and Kuiper belts; • Primitive solar system bodies (a.k.a. small bodies): i.e., the comets, asteroids, satellites of Mars, interplanetary dust, meteorites, Centaurs, Trojans, and Kuiper belt objects; • Identifying abiotic sources of organic compounds; • Origins of life and the coevolution of life and the physical environment; • Identifying, exploring, and characterizing environments for habitability and biosignatures; plus • All of the above as they relate to planetary systems around other stars. Other aspects of astrobiology, such as synthesis and function of macromolecules in the origin of life and early life, and increasing complexity are beyond the scope of this report. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-15 

Previously, planetary defense prioritization was addressed outside of the decadal survey process. This decadal survey was charged to address this topic for the first time. The planetary defense findings and recommendations in this report are presented in the framework of the National NEO Preparedness Strategy and Action Plan, which identifies NASA as the key U.S. government agency to lead such activities and directs NSF to provide support. The plan’s five strategic goals underpin the nation’s effort to enhance preparedness for dealing with the threat posed by near-Earth Objects (NEOs) and other potentially hazardous extraterrestrial impactors (NSTC 2018): • Enhance NEO detection, tracking, and characterization capabilities. • Improve NEO modeling, prediction, and information integration. • Develop technologies for NEO deflection and disruption missions. • Increase international cooperation on NEO preparation. • Strengthen and routinely exercise NEO impact emergency procedures and action protocols. This report concentrates on the first three items above. The survey’s statement of task (see Appendix A) contained a series of non-binding guidelines designed to ensure that this report contained actionable advice and maintained consistency with other recently provided advice developed by the National Academies. A GUIDE TO READING THIS REPORT The survey committee recognizes that this is a long report. Its length derives, in part, the addition to the statement of task four items not included and/or emphasized in Vision and Voyages: 1. Greater emphasis on astrobiology than the two preceding surveys; 2. Inclusion of a discussion of planetary defense and future mission priorities in this area; 3. Addition of considerations of the state of the profession and the provision of specific, actionable and practical recommendations concerning diversity, inclusion, equity, accessibility, and the creation of safe workspaces; and 4. Organizing the report according to priority research questions rather than destinations requiring defining and describing these questions. A more important reason for the length of this report is that a decadal survey, like other reports of the National Academies, is a multiuser document (Hicks et al. 2022). Different readers are looking for different things. Potential users of this report include the following: 1. Policy makers in in the U.S. Congress and their staff (likely to be most interested in the key recommendations); 2. Agency officials at NASA and NSF (likely to be most interested in the mission, programmatic and scientific recommendations); 3. Members of the planetary science and astrobiology communities (likely most interested in the programmatic recommendations and priority open questions for the coming decade); 4. Graduate students and early career researchers (likely most interested in key open questions); and 5. Undergraduate students and public (likely most interested in current state of knowledge and recent discoveries). Multiple users and their diverse needs make for a long document and some necessary repetition. The survey committee is under no illusion that every reader will start at the beginning and work their way through to the very last page. Nor is it necessary to read chapters sequential. For example, the chapters PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-16 

devoted to recent discoveries (Chapter 2) and the 12 key-science questions around which the report is structured (Chapters 4 to 15) and designed to stand alone.. Indeed, there are many ways individuals can and will read this report. As such, the survey committee has endeavored to design this report so that it is accessible to readers with varied interests and possessing varying degrees of technical sophistication. Therefore, the desires of most readers will be satisfied by the selective reading of different parts of this report. With the selective reader in mind, Table 1.2 is included as a reader’s guide. It is organized according to the topics mentioned in the survey committee’s charge and related tasks (see Appendix A). In general, acronyms are spelled out at the first use in each chapter that appear. To help readers who wish to delve into the report’s more technical aspects, a glossary of acronyms and technical terms can be found in Appendix F. REFERENCES Hicks, D., M. Zullo, A. Doshi, and O.I. Asensio, 2022, Widespread Use of National Academies Consensus Reports by the American Public, Proceedings of the National Academy of Sciences 119 (9) e2107760119; https://doi.org/10.1073/pnas.2107760119. NRC (National Research Council) 1994, An Integrated Strategy for the Planetary Sciences: 1995-2010, The National Academies Press, Washington, D.C. NRC and ESF (European Science Foundation) 1998, U.S.-European Collaboration In Space Science, The National Academies Press, Washington, D.C. NRC 2003, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C. NRC 2011, Vision and Voyages for Planetary Science in the Decade 2013-2022, The National Academies Press, Washington, D.C. NRC 2015, The Space Science Decadal Surveys: Lessons Learned and Best Practices, The National Academies Press, Washington, D.C. NASEM (National Academies of Sciences, Engineering, and Medicine) 2018a, Visions into Voyages for Planetary Science in the Decade 2013-2022—A Midterm Review, The National Academies Press, Washington, D.C. NASEM 2018b, An Astrobiology Strategy for the Search for Life in the Universe, The National Academies Press, Washington, D.C. NASEM 2018c, Exoplanet Science Strategy, The National Academies Press, Washington, D.C. NASEM 2018d, Near-Earth Object Observations in the Infrared and Visible Wavelengths, The National Academies Press, Washington, D.C. PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-17 

TABLE 1.2 A Guide to Reading This Report Topic Primary Discussion Additional Discussion Recommendations Issues Related to Nine Priority Topics Identified in the Statement of Task 1. Overview of planetary science, Chapter 1 n/a n/a astrobiology, and planetary defense 2. Broad survey of the current state of Chapter 2 n/a n/a knowledge 3a. Compelling questions, goals and Chapters 3 to 11 n/a n/a challenges for planetary science 3b. Ditto astrobiology Chapters 3 and 12-14 Chapter 22 n/a 3b. Ditto planetary defense; Chapter 18 Chapter 22 Chapter 18 and 22 4a. Recommended research traceable Chapters 4 to 15 Chapter 22 n/a to objectives and goals 4b. Recommended missions traceable Chapter 22 Appendix C Chapter 22 to objectives and goals 5a. Comprehensive research strategy Chapter 22 n/a Chapter 22 for planetary science, astrobiology and planetary defense 5b. Timing, cost, risk, and technical Chapter 22 Appendix C n/a readiness of recommended missions 6. Decision rules Chapter 22 n/a Chapter 22 7a. Human Exploration Chapter 19 Chapter 22 Chapters 19 and 22 7b. International Cooperation Chapter 1 n/a n/a 8. Intra- and inter-agency Chapters 1 and 19-21 Chapter 22 Chapters 19 and 22 collaboration 9. State of the Profession Chapter 16 Chapter 22 Chapters 16 and 22 Other Topics Discussed in the Report Apophis 2029 encounter Chapter 18 n/a n/a Arecibo Chapter 18 Chapter 22 Chapters 18 and 22 Artemis Program Chapter 19 Chapter 22 Chapters 19 and 22 Budgetary projections Chapter 22 n/a n/a Deep Space Network Chapter 19 n/a n/a Discovery program Chapter 22 n/a Chapter 22 Europa Clipper Chapter 22 n/a n/a Ground- and space-based telescopes Chapter 20 Chapter 18 and Appendix E n/a International Mars Ice Mapper Chapter 22 Chapter 19 Chapter 22 Launch vehicles Chapter 20 Chapter 22 Chapter 22 Lunar Exploration and Discovery Chapter 22 Chapter 19 Chapter 22 Program Mars Exploration Program Chapter 22 n/a Chapter 22 Mars Sample Return Chapter 22 n/a Chapter 22 Mission studies, PMCS and SDT Appendix C Appendix D n/a Mission studies, future Chapter 23 Chapter 22 n/a Mission studies, decadal survey Appendix C Appendices D and E n/a New Frontiers program Chapter 22 n/a Chapter 22 NSF facilities and programs Chapter 20 Chapter 1 n/a Planetary Data System Chapter 17 n/a Chapter 17 Planetary radar facilities Chapter 18 Chapter 22 Chapters 18 and 22 Plutonium-238 Chapter 20 Chapter 22 Chapters 20 and 22 Research and Analysis Programs Chapter 17 Chapter 22 Chapters 17 and 22 Sample receiving and curation Chapter 20 Chapter 22 Chapter 22 facilities SIMPLEx program Chapter 22 n/a Chapter 22 Technology development Chapter 21 Chapter 22 Chapters 21 and 22 Technical risk and cost evaluation Appendix C Chapter 22 n/a White papers received Appendix B n/a n/a PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 1-18