estimated timelines from crater densities or radiometrically dated samples (cf. Tanaka et al. 1992; Tanaka 2012). Construction of this stratigraphy allows extrapolation from local and regional investigations to global timelines and interpretations (Squyres 1984; Carr 2012; Fedo et al. 2022). Although vast progenitors of the martian surface are volcanic, their in situ alteration histories or subsequent redistribution(s) as sedimentary rocks provide a record of past surface processes and climate changes (e.g., Michalski et al. 2013b; Goudge et al. 2016). By incorporating local and regional observations of morphological, textural, spectral, and chemical properties at well-selected sites, an emerging stratigraphic context can be used to develop working hypotheses regarding the global environmental evolution of the entire planet (Grotzinger and Milliken 2012; McLennan et al. 2019). Understanding details of this framework will evolve as more sites are accessed and studied, as is often encountered in terrestrial field studies (Crumpler et al. 2011).

Constrain Absolute Ages of Martian Events and Tie to the Impact Record to Calibrate Crater Counts

Determining the absolute ages of geologic terrains and specific impact crater melt units is fundamental for constraining the timing of key martian events and calibrating crater count–based age models (e.g., Hartmann 2005; Giguere et al. 2021). Geochronology on Mars is crucial for addressing a range of outstanding planetary science questions, including understanding inner solar system impact processes and chronology, the history of habitability across the solar system, and refining models of planetary evolution. Age dating would also help answer Mars-specific questions, such as understanding when geologic units formed, underwent alteration, and interacted with the martian atmosphere and hydrosphere (e.g., Martin et al. 2017; Cohen et al. 2019).

For planetary bodies without samples of datable rocks, the primary method for establishing the age of geologic units and assessing their age relative to each other is impact crater counting (e.g., Fassett 2016). Crater counting is made possible because lunar terrains for which samples have been dated have been used to calibrate crater counts (e.g., Greeley and Gault 1973; Robbins 2014; Tartèse et al. 2019). This lunar-based cratering chronology has been applied to other bodies, despite the differences in impactor flux and other factors that could invalidate the application of lunar chronology. Calibrating martian crater counts with dated rock samples will advance the ability to date all martian geologic units and improve the crater counting–based chronology of the wider solar system.

A variety of rock types would be valuable for in situ dating. Measurements on igneous rocks can help constrain the crystallization ages of magmatic bodies, while geochronology of impact melt deposits can provide insights into the timing of impact events and the planet’s bombardment history (e.g., Kaneoka 1980; Schwarz et al. 2020). Sedimentary rocks may contain time-sensitive phases that offer insights into the climate history of Mars, including the timing of the transition from a wetter to a drier environment. Specific measurement techniques are discussed in the “Measurement Options” section.

Characterize Igneous Systems Within the Exploration Zone to Determine Planet Formation, Differentiation, and Volcanic History

Studying igneous systems is a priority in its own right (McSween 2015), in addition to the synergies with, and support for, other key areas of Mars and wider planetary research that this study facilitates (e.g., Tian et al. 2021). Igneous rocks on Mars preserve the most powerful, accessible, isotopic and chemical fingerprints of early accretion of any terrestrial planet. It is the only example that can be studied of an Earth-like planet that stopped growing at an early stage, well before Earth did (Dauphas and Pourmand 2011; Kruijer et al. 2017). It affords a unique opportunity to explore the tectonomagmatic systems of proto-Earths, providing unique information on how, and how quickly, planets form. From what is known from unrepresentative meteorites, Mars rapidly melted and differentiated into core, mantle, crust, atmosphere, and hydrosphere (Halliday et al. 2001). Igneous samples preserve an isotopic and trace elemental record for dating those processes and fingerprinting the mass transfer of elements as the planet first differentiated and degassed (Udry et al. 2020). This provides powerful constraints on the martian interior, including the core, as well as its atmosphere and hydrosphere (Swindle et al. 2025). The crust formed initially through igneous processes and records how a planet evolved its crust/mantle system over the first 500 million years (Nimmo and Tanaka 2005), which is almost entirely missing from Earth. Now scientists

will directly determine the earliest history of a planet, calibrated and elucidated with absolute isotopic ages of igneous rocks. Although Mars’s crust is dominantly basaltic, observations from orbiters, rovers, and meteorite studies provide evidence for a wide diversity of igneous rocks and volcanic formations that are different from those of Earth (Werner 2009). The mineralogy, petrology, geochemistry, and volcanology of such rocks can help to explain how melting, differentiation, and eruption work on other planets (McSween 2015).

REQUIREMENTS OR ASSUMPTIONS

The panel assumed that the science campaigns developed through this study will be the first human exploration missions to Mars, and human exploration will continue beyond the initial campaigns. The history of exploration on Earth has demonstrated that the most effective and efficient architecture develops a base camp with the buildup of supporting infrastructure that then enables long-term exploration as well as access to multiple sites of interest through sortie deployments. A prime example of this architecture is the U.S. base camp at McMurdo Station in Antarctica that has allowed researchers to conduct robust science deployments to multiple Antarctic sites for decades. On Mars, it is noted that the mission duration may influence human mission operations. For example, shorter 30-sol missions will likely concentrate astronaut science operations time more on sample selection, whereas 300-sol missions would allow a higher ratio of time for understanding the geologic context of the region compared to sample collection time, resulting in a more robust understanding of the site and Mars science. A 300-sol mission to Mars would enable high-priority science at Mars, support more people for longer periods of time on Mars, which increases science return, and ensure a sustainable human presence at Mars.

The current planetary science and astrobiology decadal survey highlights the importance of geosciences fieldwork by humans at both the Moon and Mars based on human expertise as mapped to achieving priority science objectives (NASEM 2023a). The panel agrees with the National Academies’ finding that the inclusion of a professionally trained planetary field scientist(s) on the crew is essential to increasing the scientific impact of human exploration missions (NASEM 2023a). This finding has been demonstrated through the Apollo experience and the successful science return based on Dr. Harrison Schmitt’s participation on Apollo 17. Substantial planetary science training will be essential for all crew members.

CAVEATS

The nature of geosciences fieldwork at Mars will be informed by precursor information and hypotheses and ultimately driven by the human experience on the ground and the human ability to observe, react, and adjust science plans based on new information. The panel strongly supports the philosophy to “[l]et the science campaigns be hypothesis-driven and strategically planned, but with the capability and expectation of being discovery-responsive” (Ashwin Vasavada, Jet Propulsion Laboratory, presentation to the panel on October 16, 2024 [NASEM 2024]). The mission architecture, including tools but also management structure, decision-making responsibility and authority, among others, is essential for enabling discovery-responsive exploration to optimize science. These decisions and advanced planning need to occur at the earliest stages of mission formulation to ensure this fundamental capability to respond to science discoveries during operations.

Multiple priority geosciences objectives also contribute to the effort to prepare for a sustained human presence on Mars. Characterizing near-surface ice reservoirs in the low- to mid-latitudes on Mars will inform in situ resource utilization (ISRU) plans and architectures. Characterizing Mars’s modern dynamic environments will also inform risk assessments and mitigations for human explorers. These overlaps with human exploration can be considered in the context of a holistic Mars exploration program. Where there is overlap between the top and high science priorities and key information for human exploration, these activities would be a priority to accomplish early in the program.

The largest single technology to enable the highest quality science on Mars is the capability to transport larger mass and volume to the martian surface. This would allow increased science by allowing advanced instrumentation, laboratory facilities, on-site sample analysis, and so on. These capabilities are ideal to enable field-informed reconnaissance of exploration sites, identify follow-up investigations while at Mars, enable high grading of samples, and

enable the ability to respond to new discoveries. The panel notes that the requirement remains to return samples to Earth laboratories to enable reproducible science results within the sample analysis communities. The technological state of the art is continually advancing. The panel expects that additional laboratory capabilities will continue to be developed on Earth that will enable sample analyses in these laboratories for decades to come. A hybrid approach to bringing laboratory capabilities to Mars as well as using laboratories on Earth is ideal. Analyses were not identified that are required to be conducted while in transit between Earth and Mars. There is a panel preference to maintain the pristine nature of samples and not risk compromising the samples by analyzing them in transit. The panel highlights the need to maintain but ideally expand data volume downlink capabilities from Mars. The increased amounts of data generated via human exploration will necessitate sending larger data sets back to Earth for additional analyses over rapid timeframes, either via refreshed orbital communication assets or direct-to-Earth relays.

MEASUREMENT OPTIONS

Significant advances in in situ analysis tools and artificial intelligence–assisted analysis are expected prior to the time of human exploration of Mars. Campaign scenarios may change over time based on these new discoveries. Sample curation technologies have to be advanced, including cryogenic sample return and other capabilities to keep samples stable, contamination free, temperature controlled, and so on. These developments need to consider all phases of sampling.

To optimize science return, astronauts on Mars would benefit from the ability to use handheld field instruments while exploring Mars and conducting fieldwork. Planning would begin at the earliest stages to develop crew-rated handheld field instruments, and the entire mission architecture would support this capability.

At the present time, techniques for obtaining isotopic ages directly on a rover are limited. ⁴⁰K-⁴⁰Ar ages have been obtained but are of relatively poor precision. New mass spectrometers are being designed for ⁸⁷Rb-⁸⁷Sr isochron dating utilizing laser ablation resonance ionization and laser ablation inductively coupled plasma ionization. At the present, the vast majority of isotopic analysis is best performed on returned samples in laboratories on Earth, where replication of results in different laboratories is possible, and the power requirements and weight of mass spectrometers are not problematic.

PRECURSOR INVESTIGATIONS

Robotic precursor investigations have been identified in the science traceability matrix that would optimize the science return from human exploration at Mars. The primary focus of precursor activity is mapping to identify optimal landing sites, inform astronaut extravehicular activities, and identify prime science sites. Precursor data from in situ measurements and/or sample return can help characterize physical and chemical hazards that may be present in martian dust and regolith. Precursor missions would provide valuable information to inform the creation of draft traverses and science sites to visit to plan astronaut surface activities.

High-spatial-resolution, accurate topographic, geomorphic, and geologic maps are a crucial input to planning human exploration. For example, these maps can be used to identify where to interrogate the rock record to identify candidate areas expected to record environmental changes, or to identify suites of lava flows and unaltered igneous rocks for study and return to Earth, including xenolithic mantle and crust material suitable for in situ chemical analyses and low-precision radiometric age measurements such as ⁴⁰K-⁴⁰Ar. Preliminary mapping of near-surface ice would be most valuable at low- to mid-latitudes (below ~47°), where the ice distribution and stability are expected to be heterogeneous, which would provide key data regarding the scale of ice patchiness to inform future human exploration locations.

POST-EXPEDITION INVESTIGATIONS

Post-expedition investigations have been identified in the STM that would optimize human exploration at Mars. Data collection from long-term monitoring stations will need to be collected following human exploration

to enable long-time baseline observations. Change detection is also enabled by long-time baseline observations to collect data to monitor aeolian and geologic changes. Post-investigation data can also monitor launch vehicle liftoff effects to characterize the blast zone and contamination. Humans on site can also measure the landing effects on the blast zone, contamination, and so on.

SYNERGIES WITH OTHER DISCIPLINES

The foundational nature of geosciences leads to significant synergies with the research areas of other panels as described here.

Panel on Astrobiology

The focus on high-priority geosciences objectives regarding characterizing and understanding the water and ice inventory and history on Mars is highly relevant to the search for life on Mars. The decadal survey for planetary science and astrobiology (NASEM 2023a) highlighted a Mars Life Explorer (MLE)-type mission as the highest priority Mars mission beyond Mars Sample Return. MLE targets low- to mid-latitude near-surface ice deposits, which is also a prime target for geosciences objectives. The geosciences objectives regarding the characterization of the rock record to understand environmental changes on Mars are directly relevant to understanding past and present habitability, because the rock record holds the history of environments on Mars.

Panel on Atmospheric Science and Space Physics

The martian atmosphere, its chemistry, dynamics, and evolution, are closely coupled with the solid planet and thus there is natural synergy with geosciences. The atmosphere has likely, in part, been sourced by the deep interior of the planet through differentiation, crustal evolution, and volcanism. Meanwhile, the crust has also been a sink for atmospheric volatiles, particularly water, over martian history. Additionally, the atmosphere fundamentally shapes geology through physical erosion, transport of material, and chemical alteration.

Panel on Biological and Physical Sciences and Human Factors

A key objective of biological and physical sciences (BPS) is to understand the integrated longitudinal martian environment and the effects on bioregenerative life support systems and ISRU applications such as crop growth. BPS aims to understand whether Mars regolith can be used as a growth substrate, particularly with respect to regolith composition and properties for ISRU applications in plant growth habitats. Regolith characterization is critical to several geosciences objectives, including, but not limited to, characterizing the dry regolith overburden in low- to mid-latitude sites to understand near-surface ice stability and vapor exchange between the near-surface ice table and the atmosphere.

SYNERGIES ACROSS GEOSCIENCES: MARS AS AN INTEGRATED SYSTEM

Geosciences objectives are intimately intertwined and highlight the importance of understanding Mars as an integrated planetary system, with relevance to other panels but also other areas of science. Below are highlighted examples of broad synergies among scientific disciplines that are key to enabling a robust understanding of Mars with applicability to broader solar system science.

Planetary Accretion

The accretion of Mars was arrested within the first few million years of the solar system, unlike Earth, which experienced a more protracted growth. As such, there is a unique opportunity to study planet formation through the isotopic fingerprints and chronometers that can be applied to carefully chosen returned samples.