A Science Strategy for the Human Exploration of Mars (2026)
Chapter: Appendix C: Panel on Atmospheric Science and Space Physics: Context for Science Traceability Matrix
C
Panel on Atmospheric Science and Space Physics: Context for Science Traceability Matrix
TOP SCIENTIFIC OBJECTIVES
The highest ranked objective of the Panel on Atmospheric Science and Space Physics is to “determine what controls the onset and evolution of dust storms.” Details of the panel’s science objectives and measurements are available in science traceability matrix format in Appendix J, but a description of why the panel ranked this as the top objective is given here. Variability in atmospheric dust loading, particularly owing to regional and global dust storms, is the main driver of present-day variability in Mars weather, climate, surface properties (e.g., albedo), and atmospheric loss rates. Global dust storms can last for months and produce huge planetwide visibility changes, atmospheric warming, strengthening of the circulation, and increased loss rates to space (e.g., Kahre et al. 2017; Guzewich et al. 2020). Knowledge of how the dust cycle operates today is key to understanding how the dust cycle may have varied in past climate epochs, which is an important input for interpreting the record of recent climate evolution contained in the dusty ice layers of the layered terrain (Forget et al. 2017). Additionally, at high obliquity, dust may stabilize otherwise unstable atmospheric conditions during Mars’s past (Kahre et al. 2013). Mars is the only accessible example of a dusty, desert planet; hence, understanding dusty phenomena (such as surface dust lifting) and their impact on the state of the atmosphere on Mars benefits studies of dust storms and aerosol feedbacks on “less dusty” Earth.
Numerical models have difficulty simulating the vertical dust distribution and many types of dust storms, especially global ones. Models are unable to predict the timing of most regional and all global storms, including whether the latter will even occur in any given Mars year (Kahre et al. 2017; Newman et al. 2022). Key knowledge gaps range from a lack of near-surface data on the link between surface dust lifting, surface properties (e.g., availability of sand and the extent to which this aids dust lifting), and environmental conditions (e.g., wind stress at the surface), to the lack of orbital data on global-scale winds and the evolving surface distribution of mobile dust and sand. This lack of understanding of dust processes and boundary conditions, and the unpredictability of most dust storms, also poses a risk for mission planning, astronaut safety, and equipment operation, which could delay achieving human mission objectives and drive costs up.
While robotic missions with the right sensor suites could make progress on the understanding of dust storms, human-aided investigations would enable detailed meteorological and aeolian (dust and sand motion) experiments (including via physical sampling of dust and sand fluxes) to determine the ideal locations for studying all aspects of dust lifting on Mars—for example, in regions with different terrain or surface properties (e.g., sand availability). Investigations would benefit strongly from the ability of astronauts to move a single, optimally outfitted sensor
station including a tall meteorological mast to multiple regions; react in real time to unusual dust events (from a flurry of dust devils to a dust storm); and expand measurements to the surface (e.g., measuring grain cohesion via physical sampling) or through the boundary layer (e.g., measuring dust vertical mixing via balloon launches during dust events), all of which would likely be cost-prohibitive with a robotic mission. The ideal sensor configuration would then remain on Mars to continue making automated measurements at an ideal site for years, covering a wider range of dust events.
The next priority tier of objectives was a group of five objectives all considered equal in priority. In a non-prioritized list, each objective is identified with a brief statement on why it is considered important. Complete information is in the panel’s science traceability matrix in Appendix J.
Determine What Controls the Present-Day Water and CO2 Cycles and the Surface/Subsurface Deposits
Along with the dust cycle, the water and CO2 cycles are the most important cycles that drive present-day martian climate (e.g., Buhler and Piqueux 2021; de la Torre Juárez et al. 2024; Montmessin et al. 2024). The north and south polar layered deposits and annual polar caps are the major sources of water and CO2 in the atmosphere. Although measurements can be made at any location, of particular interest would be near the polar layered deposits, especially in the northern hemisphere, where the bulk of the water sublimates into the atmosphere during northern summer. Profiling of near-surface atmospheric water vapor and its surface exchange are important for determining the role of the regolith as a source and/or sink of atmospheric water and the transport potential of water vapor across the planet. Better knowledge of atmospheric ice aerosol sizes and compositions is needed to characterize the radiative effects of water and CO2 clouds.
Determine How the Climate, Water, and CO2 Cycles Differed in the Ancient Past, as Indicated by Geologic Evidence
Knowing the ancient atmosphere composition and absolute age provides insights into the early climate of Mars and its habitable potential. It can also provide information that aids in understanding how the climate transitioned to its current state (e.g., Wordsworth 2016; Palumbo and Head 2018). In addition, the carbonate and sulfate minerals and the isotopic systems within capture the total atmosphere–geosphere–hydrosphere system uniquely in terms of chemistry and evolution of reaction pathways. This relates directly to the question of habitable environments through time and advancing knowledge of the evolution of Mars’s habitability through the eons. Humans on Mars would be best placed to select, obtain, and analyze rock samples as needed for most of these investigations.
Determine How the Climate, Water, CO2, and Dust Cycles Varied in the Recent Past (Up to Tens of Millions of Years Ago), as Captured by the Layered Terrain
In situ records of recent climate held in layers of dust and ice reflect the climate system’s response to known variations in orbit, and hence the strength and distribution of solar forcing, which gives insights into climate processes and feedback (e.g., Smith et al. 2020). Understanding recent climate variations also sheds light on the potential for habitable conditions in the recent past. While robotic drilling and sampling of ice is already feasible, humans would be best placed to select and reach the optimal locations and to supervise the process of in situ analysis and obtaining, analyzing, and packaging dust-ice cores and samples for return to Earth.
Determine How the Atmosphere Is Being Lost Today and How It Was Lost in the Past
Atmospheric loss has been a major factor in determining the climate evolution of Mars over its history, and hence the habitability potential over time (e.g., Atreya et al. 2013; Jakosky et al. 2018, 2021). How the early atmosphere was lost (to space and the surface and/or subsurface) and how this loss affected atmospheric composition over time are major unknowns. The study of still-active present-day loss processes and isotopes can reveal past losses. This objective overlaps with the measurements needed in the following objective.
Determine the Present-Day Atmospheric Isotopic and Elemental Composition and Its Sources and Sinks
Present-day atmospheric isotopic and elemental composition can be used to compare to what may be found in meteorites or other martian geologic samples (e.g., Atreya et al. 2013; Slipski and Jakosky 2016; VanBommel et al. 2018; Trainer et al. 2019; Webster et al. 2021; Lo et al. 2024; Vandaele et al. 2024). Variations in abundances with time and location provide information on sources and sinks and on chemical, geologic, and dynamical (e.g., transport) processes in the atmosphere, at the surface, and in the subsurface. Understanding the sources and sinks and their connections to physical processes is key to linking data from previous landed missions, orbital missions, and the meteorite record, while also linking to data from future human missions. This objective overlaps with the measurements needed with the objective above.
The remaining top objectives ranked by the panel are “determine how the surface is modified by the atmosphere,” “determine how different regions of the present-day atmosphere, from surface to magnetosphere, are linked via the transport of energy, volatiles, and dust,” and “determine how the space environment influences the atmosphere/climate.” Although also important, these objectives were ranked lower than those described above, in part because human involvement does not enable them as much as the others. However, both returned samples and present-day measurements—especially of surface fluxes associated with the present-day dust, water, and CO2 cycles—will contribute to understanding the atmosphere–surface interaction. Furthermore, observations of the present-day atmospheric state and circulation required to address most of the high-priority objectives, if made in concert with measurements of solar radiation and solar wind inputs (which may already be required for operational reasons), will add to the understanding of the last two of these objectives, for example, vertical coupling and transport, and the impact of the space environment on the atmosphere.
ASSUMPTIONS
To develop the science objectives and associated requirements, the panel made a few explicit assumptions. These assumptions can be categorized as mission architecture, engineering, and logistics. The mission architecture assumption is that, with the current proposed timeline, using humans to survey instrument installation sites and sample acquisition sites, to install instrumentation for digging, drilling, and collecting samples, and to monitor instrument performance, particularly for physical sampling of the surface and subsurface and for instruments on a tall meteorology mast, is more easily realized and would provide more samples than the robotic alternatives. The engineering assumption is that the required technology would exist in time for human exploration. The panel’s logistics assumptions include that the method of delivering astronauts and payload to the surface of Mars will provide sufficient payload mass to accommodate all the required equipment; that there will be a telecommunication infrastructure with sufficient bandwidth and performance to transmit the required data from Mars to Earth; and that there will be sufficient time within the astronauts’ mission schedule to set up the instruments and take the measurements and (where relevant) samples required to meet each objective.
CAVEATS
The panel recognized that some of its lower-priority objectives could be met by robotic systems with modest or no human involvement. Benefit from astronaut involvement thus changed the priority. However, from both a purely scientific perspective and a human-involvement perspective, the top priority remains understanding the dust cycle.
The prioritization of some objectives carried tacit assumptions about the accessibility of different sites on the martian surface. Notably, for recent climate history, the polar ice caps offer a particularly attractive record (though other locations would also be acceptable [e.g., mid-latitude debris-covered glaciers]). High-latitude regions may be considered inaccessible owing to considerations of temperature, illumination, orbital mechanics, or perceived terrain hazards. If a human exploration architecture were to invoke in situ resource utilization—for example, to produce methane or hydrogen rocket propellant from water ice—then the required equipment may make the acquisition of ice cores easier than for rock or sediment, and the cost/benefit proposition changes dramatically.
MEASUREMENT OPTIONS
For many of this panel’s objectives there is a need to understand the response of the atmosphere and surface to changes in forcing, as well as feedbacks within the entire system; hence, in situ measurements are vital, as the Mars system and its drivers cannot be returned to Earth for study.
The panel discussed various options for probing the atmosphere in the boundary layer (up to ~10 km). Soundings to arbitrary altitudes may be accomplished by rocket-borne instrumentation, whereas there will be practical limits to the altitudes attainable by balloons (Noga et al. 2023). Either option benefits from astronauts being able to select the proper location and timing for such launches. For probing the lower altitudes, expendable measurement platforms may require more mass in the long term than reusable vehicles such as drones that could return to their launch site for recharging. However, drones are limited in their maximum payload mass, owing to the low atmospheric density, and thus may not be able to carry the instrumentation required for the scientific measurements. Near-ground profile measurements can be accomplished by permanent rigid masts, deployable masts that can be retracted during dust storms, or tethered balloons. The advantages and disadvantages of these respective platforms may be quite different from those on Earth, given the martian atmospheric density, gravity, and wind environment, and require future study.
While Mars atmospheric science and space physics has benefited from direct measurements of the atmosphere, both via orbiters and landed spacecraft (e.g., Viking [Nier and McElroy 1977]; Curiosity [Mahaffy et al. 2013; Martinez et al. 2017]; Mars Atmosphere and Volatile EvolutioN [MAVEN]: [Jakosky et al. 2015]; Hope [Almatroushi et al. 2021]; and ExoMars Trace Gas Orbiter [López-Valverde et al. 2018]), each has its own set of disadvantages, uncertainties, and gaps. Human involvement in the measurements and collection of samples offers a great opportunity to acquire simultaneously the full set of measurements that are needed on the surface, in the near subsurface, and in the boundary layer to address questions that have not been able to be addressed by the prior missions.
Collecting atmospheric samples requires specific containers with surfaces and materials free of adsorbed and embedded volatiles and tight, leak-free seals. An in situ sampling and sample return, human-in-the-loop approach would allow those problems to be overcome. In situ sampling and measurements can be combined to alleviate problems with reactive gases (e.g., methane, a possible biomarker) and measurements of the least abundant isotopes, which are important tracers of atmospheric evolution. Sampling and in situ measurements would benefit from real-time decision making (e.g., on the exact moment of sampling in relation to wind) and easy ability to sample at multiple heights. The focus would be on sampling close to the surface to capture any potential processes such as outgassing.
Sampling for return of atmospheric samples would be in stainless steel containers, prepared through electropolishing and outgassing under ultravacuum before the flight. This is a common technique for terrestrial sampling and would guarantee that inorganic gases such as noble gases are transported back safely and without loss. Organics are harder to preserve but could be measured with portable instrumentation or absorbed on specific columns, also a common terrestrial technique. All techniques could be used in parallel by a human operator on “same sample” locations so that the result will be a set of samples that allows the full suite to be measured in a combination of in situ and returned samples. For literature on the subject see, for example, Jakosky et al. (2021) and Swindle et al. (2022).
Sampling of dust, ice, regolith, and rock samples is also important to accomplish the panel’s top objectives (e.g., Beaty et al. 2019; Albert and Koutnik 2021). Rock samples, including their mineralogy, geochronology, and in particular the composition and isotopic ratios in remnants of past atmospheric gases contained within them, provide information on past climates dating back as far as billions of years. The thickness, composition, and isotopic ratios of dust-ice layers in ice samples provide information on more recent past climate change. Such layers may be sampled by taking deep vertical cores from an ice cap or subsurface ice deposit, or by accessing different stratigraphic layers (hence ice ages) in ice deposits for which a deep vertical profile is exposed at the surface (except for a thin dust lag). Regolith samples provide information on topics varying from dust composition and grain sizes (for atmospheric, engineering, and human biology purposes) to the integrated signature of high-energy radiation at the surface.
PRECURSOR INVESTIGATIONS
Many of the objectives identified by this panel require precursor landing site information to select landing sites for human missions and would strongly benefit from precursor and contemporaneous orbital measurements.
The landing sites that are ideal for the objectives vary, but all require precursor information on the safety and appropriateness of the landing site to meet the measurement needs (e.g., presence of local dust lifting, access to ice–dust layering; e.g., Golombek et al. 2012). There currently exists a good amount of atmospheric and surface/subsurface information to guide the community in landing site selection; however, only 4 percent of the surface has been covered by the highest resolution imaging (via Mars Reconnaissance Orbiter [MRO] High Resolution Imaging Science Experiment [HiRISE]). Specific locations that could be considered for landing a human mission likely do not have these highest resolution data to certify the safety and appropriateness of the landing site. This asset would likely need to be replaced and operable within a few years of the humans landing, and it would be ideal to continue such an asset throughout the entire intervening time. Site selection can take many years to converge on the most scientifically valuable and safe locations, requiring high-resolution imaging as well as information on rock abundances, thermal inertia, slopes, surface and subsurface ice abundance, and likely other requirements that may manifest in the future. With respect to ice, rock, and regolith sampling, the sampling objectives could be accomplished by one or a few deep drills or coring, or vertical sampling of an exposed column, or by horizontal traverses of stratigraphic columns that are suitably exposed by erosion, with many shallow samples (beneath modern alteration depth, approximately 2 m). Identifying the topography and other characteristics of candidate sampling sites would need to be considered in conjunction with the mobility and sample acquisition hardware required for each landing site, as they could be very different. Other desirable precursor landing site selection measurements include near-subsurface (0–10 m) ice/layering detection, dune availability and migration rates, and evidence of dust lifting activity.
The panel’s objectives are significantly enhanced by contemporaneous orbital measurements. Interpreting observations of atmospheric processes at any landing site is greatly improved by placing those observations in the context of the global atmospheric state during the same period. Because the atmosphere behaves differently on a variety of timescales (diurnal to seasonal to interannual) and both dust and volatiles are transported throughout the system, the measurements taken at the local scale can best be understood in this global context. For example, landing site observations of surface–atmosphere dust and water vapor fluxes (plus their meteorological and surface drivers) are of greater benefit when paired with orbital observations of the meteorology, surface conditions, and dust and water activity at that location, as well as orbital observations of the dust and water cycles and atmospheric circulation across the entire planet. That is because the in situ data provide vital “ground truth” boundary conditions for validation purposes and to anchor theoretical and modeling studies of the system as a whole.
POST-EXPEDITION INVESTIGATIONS
Any meteorological instrumentation that is brought and assembled by humans would be expected to remain in operation long after the astronauts’ departure (like the Apollo Lunar Surface Experiment Package). This would offer considerable scientific advantages. Atmospheric monitoring at the landing sites would continue well beyond the 30- or 300-sol mission(s), capturing weather phenomena not only on diurnal and seasonal scales but also on annual and interannual scales. Such autonomous measurements would significantly enhance the scientific value of the overall investigations and maximize the chances of making measurements during rare events (e.g., global dust storms; Martín-Rubio et al. 2025). These meteorological stations would be equipped with a range of sensors designed to measure surface-level water vapor volume mixing ratio, high-frequency three-dimensional wind velocity, and the horizontal wind profile as a function of height (both of which provide friction velocity and hence surface wind stress), air pressure, air and ground temperature, surface albedo, and optical depth of dust and water ice aerosols, as well as their particle size distribution. Sensors would monitor the upward and downward, diffuse and direct, solar and thermal radiative fluxes, in addition to high-energy radiation at the surface (including ultraviolet, gamma rays, and energetic ions). Other instrument packages to remain operating may also include those deployed to monitor surface ice frost and measure the absolute water vapor content near the surface. Ideally, less
frequent measurements through the boundary layer or lower atmosphere could also continue (via light detection and ranging [LiDAR], or via remote deployment of balloons, drones, or rockets) after humans leave.
The long-term communications and power infrastructure to support such operations will need to be built into mission planning.
SYNERGIES WITH OTHER DISCIPLINES
Dust is a major player in shaping the geologic landscape of Mars and has contributed to the sedimentary record throughout Mars’s history. Understanding modern processes will inform knowledge about the past. For example, the abundance of dust and its variation in layered terrain reflects different climate epochs. Dust is the product of rock erosion, with the physical processes creating the finest grain sizes and mineralogical reactions creating secondary minerals, such as phyllosilicates (Panel on Geosciences synergy). Once deposited, dust is the basis of fine-grained sediments, which are both informative for past climate and have high preservation potential for biomarkers (Panels on Geosciences and Astrobiology synergy). On a dry world such as today’s Mars, the surface rearrangement of dust results in the largest surface changes observed. Dust has the capability to transport microorganisms, but it also can act as a shield against radiation (Panel on Biological and Physical Sciences and Human Factors synergy), a nutrient source, or a basis for adsorption.
Atmospheric composition and the abundance of the main and trace constituents (water, CO2, nitrogen, oxygen, etc.) are key players to shape the morphology of the surface through physical weathering and material transport. Atmospheric density strongly affects aeolian activity and planetary temperature, and thus the availability of dust and water (Panel on Geosciences synergy). The chemical constituents in the atmosphere contribute to temperature control and the availability of species and, thus, directly to chemical weathering processes and mineral formation as well as habitability (Panel on Geosciences and Panel on Astrobiology synergy). They are documented in both the isotopic fingerprint of atmospheric constituents and the geologic rock record. Interactions of the atmosphere with loose material on the surface, and with the surface and shallow subsurface, form archives of past climate and geologic processes that can be studied (e.g., polar layered deposits, ice cores, and layered rock strata) to understand the past (Panel on Geosciences synergy). Both the atmosphere and the rock record hold information on the radiation environment—present and past—of Mars (Panel on Biological and Physical Sciences and Human Factors and Panel on Astrobiology synergy). Thus, the ice and rock record contains information through “classic” mineralogical and geochemical aspects studied by the means discussed in the geosciences panel and at the same time elemental and isotopic information that is directly related to atmospheric evolution. The atmospheric record trapped in the rock record provides information on past climate and the current atmospheric behavior gives an anchor point. The volatile inventory through time is also represented by the current atmosphere combined with the record of past atmospheric conditions in the rock and ice records (Panel on Geosciences and Panel on Astrobiology synergy).
SYNERGIES WITH OPERATIONS
Monitoring of environmental hazards will almost certainly be required to ensure the safety of human explorers, both in space and on the surface. Arguably the greatest hazard to human explorers is energetic charged particle radiation, both galactic cosmic rays and solar energetic particles (Schwadron et al. 2010; Guo et al. 2021). Instrumentation to monitor the Sun and the solar wind is critical for ensuring human safety. These measurements also have high scientific value. For example, in combination with the measurements of the present state and dynamics of the atmosphere, they allow determination of the influence of the space environment on the atmospheric state and atmospheric escape, as well as the importance of vertical coupling processes.
Conversely, the scientific measurements required for monitoring of environmental hazards also have operational value. Measurements of the atmospheric state, particularly dust properties and dust-induced atmospheric variations up to and including dust storms, help ensure human safety on the surface. For example, the potential risks are a decrease in visibility and solar power during a dust storm; buildup of dust on solar panels if removal events or cleaning does not occur; damage by dust and sand (during storm conditions or dust devil passage in particular) to optics, delicate sensors, filters, lubricants, and so on; and damage to human lungs (especially also
some chemical aspects of it [e.g., perchlorates]) or equipment. In addition, locating deposits of accessible ice (surface or near-subsurface ice or hydrous minerals) could aid in situ resource utilization efforts. Dust events pose a risk for mission planning. For example, major storms strongly impact atmospheric density and winds, which are critical during mission phases such as aerobraking and entry-descent-landing operations, and they impact visibility and solar energy during surface operations (Newman et al. 2022).
The infrastructure required for delivery and return of human explorers, as well as communications, provides additional opportunities to accommodate science instruments that make valuable observations. For example, the main crew vehicle can drop off secondary payloads, including orbital assets or descent probes. An areostationary network in orbit can be used for relay, atmospheric observations, and space weather monitoring, and would aid prediction of dust storm activity as an early warning system.
TECHNOLOGY ADVANCEMENT IMPACTS
Human missions to Mars will significantly benefit from the technological advancements currently being developed for the Artemis program. Several technologies, directly relevant to the measurement objectives prioritized by this panel, are anticipated to have a significant impact. These include technology for deployable masts, originally designed for drilling, energy generation, and illumination (e.g., the Deployable Interlocking Actuated Bands for Linear Operations; Sanigepalli et al. 2024), that may also be adapted for meteorological applications, as well as systems for sample storage, extravehicular activity operation (encompassing astronaut suits and robotic assets), and portable geologic laboratories.
The advanced systems for sample drilling, transport, storage, and handling being developed for Artemis will directly contribute to the broader Moon to Mars campaign (e.g., Stolov et al. 2023). Noteworthy progress is being made in cold sample return technology, ensuring the secure handling and transport of volatile-bearing samples.
Anticipated improvements in sample analysis instruments, alongside the development of more sophisticated laboratories, are expected to assist human explorers in performing in situ triage. These systems will enable astronauts to prioritize and select samples for further analysis on Earth.
Other technological advancements that will have a direct impact on this panel’s objectives are expected to arise from the development of aerial vehicles capable of directly sampling the atmosphere at various altitudes, something not yet achievable through surface or orbital measurements. These vehicles, including drones, balloons, or rockets, will facilitate comprehensive atmospheric characterization. Advancements in sensor technology, coupled with improvements in the robustness and accuracy of a wide range of surface and subsurface sensors, are anticipated in the near future. These innovations will be further enhanced by developments in artificial intelligence (AI), with AI-driven systems working alongside humans making possible a deeper level of collaboration between humans and robotic assets for more efficient operations.
