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Panel on Astrobiology: Context for Science Traceability Matrix

INTRODUCTION

The Panel on Astrobiology derived the highest priority astrobiology goals and measurements for the first human campaigns on Mars based on panel expertise and existing studies (e.g., NRC 2007; MEPAG E2E-iSAG 2011; Mustard et al. 2013; Beaty et al. 2019; NASEM 2019, 2023a; Carrier et al. 2020; NASA 2023c, 2024d). The objectives and measurements were designed keeping in mind that astrobiology is a rapidly evolving field of research and that discoveries will be made in the coming years. Details of the panel’s science objectives and measurements are available in science traceability matrix format in Appendix J.

Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This spans many questions, from abiotic organic chemistry and the origin of life, to how a biosphere can affect its environment, to where life might be found, to what the future of inhabited planets might look like. Astrobiology is a heavily interdisciplinary field requiring inputs from a wide range of expertise from biology and chemistry to sociology and understanding the implications for society of discovering life beyond Earth. This interdisciplinary nature is well suited to take advantage of the integrative capabilities of astronauts during exploration. As a rapidly expanding field, astrobiology has advanced beyond “looking for life elsewhere.” In planetary science contexts, it is important to infuse missions with goals that emphasize major questions of astrobiology, such as the origin of life, habitability, diversification of life, and whether life could or did exist on other worlds.

One of the four goals of the Mars Exploration Program (MEP) (NASA 2024d) is to “determine whether life ever arose on Mars,” which includes subgoals about habitability and biosignatures. The MEP’s goals of characterizing the climate and geology of Mars also address astrobiology issues in their subgoals. Examples include the warm wet environments of ancient Mars, the past surface radiation environment as inferred by paleomagnetism, and Mars’s aqueous history as inferred by rocks and minerals. These are all consistent with NASA Science Mission Directorate’s key questions: “How do planets and life originate?” and “Are we alone?” (NASA 2024g).

Part of astrobiology is exploring new conditions in which life can exist and thrive. Mars offers the most accessible means of exploring whether life can exist in a substantially different way than it does on Earth. The study of life in the universe will add to the understanding of life on Earth, the potential of life elsewhere, including exoplanets, and the relation between planetary evolution and life. The discovery of life elsewhere may affect society’s concepts of the role humans have in the universe. It is important to be mindful, explore responsibly, and prepare for how to respond if astronauts discover extant life on Mars.

OBJECTIVES

Three top-priority and eight high-priority astrobiology scientific objectives were identified for human exploration of Mars (see Appendix J). These objectives are grouped under four categories: The Origin of Life, Habitability Through Time, The Search for Life, and Characterizing Life If It Is Found. There are many nuances to studying astrobiology of other worlds, whether on Mars, inside an ocean world, or on a planet orbiting another star. The general starting point is what is known about life on Earth. Yet it is not known how life started here or the full range of capabilities that life on Earth contains. There is a vast chemistry space in the solar system that creates a range of different options for how life could potentially form and evolve. Astrobiology must take care not to take an Earth-centric approach. The objectives outlined here take into account the basic measurements needed for prebiotic chemistry, habitability, and life as it exists on Earth, as well as measurements needed to understand and evaluate other kinds of organic chemistry. This strategy is designed to be as universal as possible, to identify non-Earth-like life if possible, and to interpret the source of complex organic identifications in a non-Earth-centric framework. For example, to search for habitable environments, prebiotic chemistry, or signatures of life, it is essential to characterize the environmental context at a landing site. It is also important to revise this strategy as astrobiology research progresses in the time between now and a crewed mission to Mars, to take into account new discoveries (e.g., environmental sciences, biotechnology, or origin of life on Earth).

Determine If Evidence Can Be Found for Extant or Extinct Life

The highest priority astrobiology objective identified for human exploration of Mars is to determine if evidence can be found for extant or extinct life at the landing site(s). This question is contained within the “distribution of life” aspect of astrobiology which is a subpart of Goal 5 in An Astrobiology Strategy for the Search for Life in the Universe (NASEM 2019); searching for life is the focus of Question 11 in the most recent planetary science decadal survey, Origins, Worlds, and Life (NASEM 2023a), and features in strategic documents (e.g., NASA 2015, 2025b).

This objective is divided into five sub-objectives that are needed to provide context and evaluate the potential for putative biosignatures to be true signs of extant or extinct life. The sub-objectives cover structural characterization of organic matter, isotopic fractionation of organic and inorganic materials, inventorying micro- and macrostructures, identifying potential biominerals, and measuring the degree of disequilibrium of the sample site. These measurements have been prioritized in the biosignature community (Mustard et al. 2013; Neveu et al. 2018) and cover features of a physical lifeform and of biological processes. The need for further definition of a measurement strategy (e.g., a decision tree) is discussed below.

Determine If Niche Habitats Exist on Mars Where Life Could Have Survived

The next top-priority objective is to determine if niche habitats—habitats that are not spatially or temporally extensive where life as we know it could have survived—exist on Mars. This objective leaves open what a niche habitat could be, listing known examples as possibilities but also allowing for new discoveries to be made.

Habitability—contained in the “distribution of life” aspect of astrobiology—is defined as environments or conditions where life could survive. It is a broad list of conditions, as life on Earth has diversified into many environmental niches. Habitability can also be viewed as a degree, to differentiate between conditions where life survives versus where life thrives or is found in abundance. The Astrobiology Strategy (NASEM 2019) defined the concept of “dynamic habitability,” the changing degree of habitability of a planet with time. This is important for Mars because its climate has changed dramatically in the past 4 billion years from its warm and wet past. It is important to conduct measurements not only in locations that are recently habitable based on the understanding of life on Earth, but to also choose locations that may have been important in Mars’s dynamic habitability and/or where life could thrive on Mars today. Earth has also changed in key ways in the past, so much so that in some respects it more closely resembled an alien planet than modern Earth.

This objective is a top priority because it narrows down the areas to search for extant or extinct life. For a shorter-duration mission, this objective has higher priority as a first step for identifying the optimal location for

REQUIREMENTS OR ASSUMPTIONS

Objectives Excluded from the First Human Campaigns

Some high-priority objectives identified in previous studies (NRC 2007; Mustard et al. 2013; NASEM 2019, 2023a; Carrier et al. 2020; NASA 2023c, 2024d, 2024g) were not included because they were deemed to be either too broad or not possible to achieve during a single campaign. For example, it is not possible to define any series of measurements that would provide the definitive answer that life did not and does not exist on Mars. Furthermore, how Mars’s planetary evolution would have proceeded in the presence or absence of a biosphere is also difficult to answer with measurements during the first human campaigns.

The Importance of Humans to Astrobiology Exploration

Astronauts will be uniquely suited to enable the astrobiological exploration of the landing area, in situ investigation at priority sites, and the collection of carefully characterized samples for return to Earth. Lessons from Apollo and terrestrial human analog tests have demonstrated the unique advantages of having highly trained astronauts quickly survey the geology of a site, adapt to new information, formulate new hypotheses, and identify the best samples to collect for further analysis. This near-real-time feedback process enables astronauts to cover more ground than robotic explorers and to conduct hypothesis-driven adaptive exploration.

The importance of in-depth on-site astrobiology investigations has been demonstrated in terrestrial field studies in extreme environments finding life in microhabitats. Although robotic precursor missions can be used to identify potential habitable regions on Mars, it is the astronauts on the ground who will make the fine-scale contextual observations needed to identify potential niche habitats. What can be achieved in the first campaigns will depend on the quality of precursor information and the time allotted for astronaut exploration of the landing area.

Equipment Needs

It is assumed that the astronauts are equipped for science-focused surface exploration in complex geologic environments: mobility systems capable of handling challenging terrain, handheld equipment, and techniques enabling specific science investigations in the field and in the habitat and/or laboratory. It is assumed measurements will be performed in the field using portable instruments as well as on collected sample material returned to the habitat. It is assumed the habitat will include a clean, optimally sterile laboratory environment with laboratory instrumentation.

For measurements in the field, it is assumed the astronauts will have the ability to do walkabouts and potentially have access to a vehicle to cover larger distances. It is assumed the astronauts and mission control will have a shared spatial context, based on orbital imaging and surface vision, for orientation in the field and tracking of astronaut positions by mission control and scientists in the loop.

Visual and spatial awareness forms the first tier of any strategy for investigating and understanding geologic context. This includes multiscale, stereo, and multispectral imaging. A Mars compass, and a portable 3D camera with mapping capabilities and a zoom, coupled to a continuous data recorder, would enable such imaging. A drone equipped with a camera would be useful. The data could then be fed into a geographic information system.

It is assumed that the astronaut suits are suitable for field geology and that portable tools and instruments are compatible with the dexterity of the astronaut’s gloves and range of mobility. Classic field geology tools include at least a hammer and a tape measure or range meter, in addition to the imaging capabilities previously mentioned.

Portable science instruments can be used to identify and select regions of interest and samples for astrobiology science, including the above-mentioned cameras and a handheld ultraviolet–visible–near infrared spectrometer. Specific measurements may require other spectrometers, a magnetometer, a residual gas analyzer, or portable ground-penetrating radar (GPR) on a cart. These instruments will need a portable power source or rechargeable battery packs and a data recorder. Available rover instrumentation could be modified for this purpose or for use in the laboratory.

A portable drill or corer, sample handling equipment, and bar-coded, sterile, airtight sample containers are basic equipment for sampling. Contamination and cross-contamination must be avoided. For deep drilling (>1 m), drilling rigs will be needed, either fully robotic or astronaut operated. For transporting tools and samples, a field backpack or a small cart is recommended.

Astrobiology investigations may require access to regions that have a high potential for existence of martian lifeforms or regions that are difficult or dangerous to access. To decrease the risk for contamination or injury, a human astronaut could work with robotic technology such as a rover or helicopter for investigations and sampling.

In situ analysis of samples is preferable. If a sample cannot be investigated in the field, then a laboratory inside or attached to the habitat could be available. The samples need to be stored in a stable temperature environment (average annual Mars surface temperature for short-term storage, and −80°C for long-term storage) and protected from exposure to radiation and oscillations. All samples need to be treated in an identical manner. A miniaturized chemistry laboratory, coupled with dedicated analytical instruments, would be valuable.

The astronauts may not necessarily be trained astrobiologists, and they will have to concentrate on other mission needs. To maximize the science output, it will be important to have geologists, chemists, and biologists in the loop.

CAVEATS

Planetary Protection

There is a critical synergy between planetary protection and astrobiology, both in the conduct of research and the results obtained. Results from addressing astrobiology objectives inform planetary protection requirements. Conversely, planetary protection requirements could limit sample acquisition and methodologies for astrobiology objectives. No assumptions were made concerning planetary protection requirements. Addressing astrobiology objectives on Mars through human exploration will be challenging unless specific issues are resolved through development of policies. A few of the issues are discussed here.

A significant concern is forward contamination: human activity contaminating the Mars environment with biological species from Earth. Managing forward contamination is particularly important for the detection of biosignatures to ensure that anything detected is truly part of the martian environment. The most recent planetary protection requirements to address this concern, described as encapsulated bioburden, would prohibit astronauts from landing on Mars. This suggests potential disconnects between existing planetary protection policy and achieving astrobiology objectives on Mars.

Many knowledge gaps related to forward contamination could be addressed with precursor studies. This could include constraining measurements needed to detect false positives, better understanding how common organics are on Mars, quantifying the volume of contamination released by spacesuits and habitats, concerted modeling studies of transport of contamination, and quantifying the biocidal effects of the Mars environment to determine what will survive and for how long.

A precursor mission to the selected landing site could be valuable for in situ characterization prior to sending humans. This provides a benchmark for comparison once humans arrive and after they leave and would include global long-term monitoring beyond the landing site, such as a meteorological station. During the mission, Earth-based control experiments could be performed in parallel to help constrain potential contamination, followed by long-term monitoring after humans leave, in case forward contamination is observable after an extended period. Last, a plan for how to handle contamination beyond a predetermined limit could be useful. Lessons learned from expeditions on Earth to sensitive areas, including cases where contamination caused significant damage, could provide useful guidelines in planning.

Some regions on Mars are designated as Special Regions—off limits for unsterilized exploration to protect them from forward contamination. Many Special Regions have the highest potential for finding extant life. Site selection could be handled holistically and include public release of candidate site listings and public discussion of concerns. Advanced planning to mitigate the impact on the site by leveraging human–robotic partnerships such as rover and drone technology could be valuable. Selecting a landing site far enough from the Special Region to reduce human impact, and yet close enough for remotely operated vehicles to explore, could also be valuable.

There is the potential for backward contamination when an astronaut discovers suspected evidence of life. Such a discovery would generate a range of public responses. Multiple lines of investigation addressing the possible discovery of life could diminish the potential of terrestrial contamination being mistaken for extraterrestrial life (a false positive), help characterize the nature of the purported martian life (including level of activity and biological requirements), and inform methodologies for containment and precluding propagation. Clearly defined planetary protection policies and proactive measures to address concerns are essential to protect Earth and the astronauts.

Needed Research and Development

Two areas need development: a decision tree for the search-for-life objective and determining the minimum sample size to achieve these objectives.

A decision tree defines measurement steps where the next set of measurements is defined based on the previous measurement results. This report defines measurements that are necessary to achieve the science objectives. Insufficient time was available to define an order of operations for analytical protocols and criteria for decisions to proceed that depend on prior results. There are measurements that would only apply if a previous condition were met. A future study could be conducted to refine the suggestions and procedures outlined here by providing an order of measurements and decisions that would be followed to achieve the science objectives. The timing of this report coincides with the finalization of the Mars Sample Return Sample Receiving Project Measurement Definition Team 1 report (Carrier et al. 2025), which is relevant to many considerations for the astrobiology objectives but was not available until after the panel concluded its work.

More research and preliminary in situ measurements will be needed to determine the minimum sample size. Determination of minimum sample mass requirements will be based on the measurements to be done on Earth, the technology available, specifics of the mission, and the state of knowledge of Mars samples.

PRECURSOR INVESTIGATIONS

Baseline for Forward Contamination

Monitoring of the exploration zone by robotic precursor investigations can determine if there are Special Regions too close to the landing site and provide a baseline characterization of the landing site prior to human arrival, which would establish the pristine levels (such as organic carbon baseline) before the introduction of contamination from human exploration.

Niche Habitat Mapping

Identifying and evaluating the habitability of niche habitats is crucial for the search for life given that these sites are the most promising for hosting extant life (Carrier et al. 2020). A robotic precursor mission (rover or orbiter) would narrow down promising landing sites for human explorers. The panel divided niche habitats into two categories: near surface and deep subsurface. Potential landing sites hosting surface niche habitats could be determined from detailed topographic and geomorphological mapping of the surface down to 20 m depth (Mustard et al. 2013). Caves could be inferred from synthetic aperture radar and GPR measurements, and mineralogical analyses could be used to deduce the geochemistry of putative caves.

POST-EXPEDITION INVESTIGATIONS

Forward contamination may occur at levels too low to detect during the time when humans are on the surface, but biological contamination may grow to detectable levels in months or years after humans return to Earth. Monitoring the exploration zone in the long term can ensure detection of contamination that requires an extended period of time to manifest.

SYNERGIES WITH OTHER DISCIPLINES

Geosciences

There is a strong synergy between astrobiology and geosciences on Mars. From the astrobiology perspective, it is vital to understand the geologic context of any region studied, whether searching for evidence of prebiotic chemistry, evaluating habitability through time, or detecting biosignatures. Many of the measurements needed to achieve astrobiology objectives are also valuable for geosciences objectives. A high priority for astrobiology is to characterize the elemental and isotopic composition of rocks, ices, liquids, and gas on Mars. Observations of composition with direct overlap with geosciences include understanding mineralogy, volatile and organic composition, inorganic composition, geochemistry, and impacts of aqueous geochemistry. There is also synergy in establishing the exposure age and geochronology of the rock record for all areas explored and samples collected as well as constraining the history of the magnetic field.

Atmospheric Science and Space Physics

The strongest synergies between atmospheric science and astrobiology are related to volatile abundances and composition in the current atmosphere and establishing the climate history of Mars to constrain the atmospheric composition through time. As with geoscience, characterizing history of the magnetic field as well as the elemental and isotopic composition of volatiles found in rocks, ices, liquids, and gas on Mars provides the most valuable synergy. Of particular importance for astrobiology is constraining the history of water on Mars and the role of atmospheric loss in this history.

Biological and Physical Sciences and Human Factors

Astrobiology and biological and physical sciences (BPS) both share an interest in understanding life and the impact of the Mars environment on life. While the astrobiology objectives work to characterize the habitability of the landing site environment, the BPS objectives evaluate the ability of Earth life to adapt to the martian environment. Observations that characterize the elemental and isotopic composition of rocks and the regolith as well as volatiles, including water, contribute to both disciplines. If life is discovered on Mars, the BPS and human factors objectives related to astronaut health will play a vital role in preventing backward contamination and ensuring the safety of the astronauts when conducting experiments to characterize life. Several of the measurement techniques that are suggested for BPS objectives could be adapted for studying extant life if it is discovered.

TECHNOLOGY ADVANCEMENT IMPACTS

For field geology on Mars with a focus on astrobiology, a combination of robotic and human investigations is ideal. For planetary environments that are inaccessible for humans or where humans present an unacceptable risk to biologically sensitive sites, autonomous robots could do the job, controlled by a nearby astronaut. The current generation of robots is not yet ready for some of the tasks. Advancements are needed in novel types of mobility, autonomy, and interactivity (e.g., robot handing over a sample to an astronaut) to support in situ astrobiology in the field.

Astronauts will use a range of portable and handheld science instruments in the field. These can be portable or laboratory versions of existing science instrumentation used on rovers and landers but need to be modified for use by astronauts.

NASA’s current Mars program has focused primarily on looking for evidence of habitability and signs of past life. To investigate the existence of extant life on Mars, a range of life-detection instruments are required. Currently, the number and sensitivity of detection methods that could be implemented if samples were returned to Earth greatly exceed the methodologies that could be used at Mars. Only a subset of the investigations that are