A Science Strategy for the Human Exploration of Mars (2026)
Chapter: Appendix D: Panel on Biological and Physical Sciences and Human Factors: Context for Science Traceability Matrix
D
Panel on Biological and Physical Sciences and Human Factors: Context for Science Traceability Matrix
The Panel on Biological and Physical Sciences and Human Factors (BPS/HF) comprises two distinct research areas, and priorities were allocated equally to reflect the dual nature of the many possible directions of research. The Mars environment is complex and unique, affecting all biological species (including humans), as the integrated longitudinal martian environment (ILME). A detailed elaboration of all of these factors cannot be provided here. The ILME includes multiple crucial environmental stressors (such as dust, radiation, and circadian differences) that are both individually impactful and potentially interacting in as-yet-unknown ways for organisms on Mars. A stressor beyond what an organism can handle can cause physical damage. This stressor could be a physical factor, such as radiation, or a psychological factor, like having Earth out of view. Allostasis means an individual organism (plant, animal, or human) is able to meet the stresses adequately, but, as allostatic load increases, damage can occur. The term allostatic load is used (Sterling and Eyer 1988; McEwen 1998; Guidi et al. 2021) to refer to all the stresses, both physiological and psychological, that could impair a crew member or reference biology (microbes, plants, or animals) on Mars.1
PRIORITIZATION PROCESS
The panel’s top priorities are all crucial to a successful long-term mission by humans on the surface of Mars. The top scientific objectives study the three inextricably linked living “subsystems” in the mission (humans, plants, and microbes) and the fourth studies the performance of the crew. The scientific objectives identified by this panel study aspects of the “human exploration system” (HES) during missions on the martian surface. Details of the panel’s science objectives and measurements are available in science traceability matrix format in Appendix J. The HES consists of living components (animals, including crew, plants, and microbes), the inhabited environment (lander, habitat, rover, extravehicular activity suit, and launch vehicle), and systems operated by the crew (e.g., in situ resource utilization payloads). The top four objectives study two aspects of the HES as it is exposed to the
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1 The number of potential stressors in the martian environment affecting organisms, including human health and performance, is too vast to enumerate in this document; furthermore, the individual and interactive effects of these stressors is unknown. “Allostatic load” is used as a general description to consider the entire spectrum of factors that may affect human physiology, psychology, or social behavior and performance. Prior uses of “allostasis” or “allostatic load” in the literature may focus on only a subset of these factors; no such limit is assumed in the Panel on BPS/HF’s use of the term.
ILME: the health of a living system (animal, plant, or microbe) and the crew performance. The high objectives examine subsystems of the HES in greater (mechanistic) detail, other ILME factors, varying crew procedures, and the use of model organisms.
The four top priorities are critically integrated. The loss of microbial species or plant viability could result in catastrophic degradation of animal or human health and crew member task performance (Blaser and Falkow 2009; Douglas et al. 2021; Fan and Pedersen 2021; Nishijima et al. 2025). Ethically and operationally, the highest priority research conducted by humans on the surface of Mars will include research that elevates crew safety from dangerous conditions to levels at which the crew can thrive rather than just survive. Potential research benefits include the extension of useful mission duration, effective crew performance on the surface of Mars, and an increase in research productivity. An overarching goal for HF science priorities is the ability to increase safety margins for the crew with associated increases in outcome science return across all science strategies.
BIOLOGICAL AND PHYSICAL SCIENCES PRIORITIES
The two top priorities for BPS focus on microbes and plants, respectively. Although primary aspects of each are described below, it is important to highlight that plants and microbes together form the foundations of bioregenerative life support systems (BLiSS) habitats (Salisbury 1999; Walker and Granjou 2017; De Micco et al. 2023) essential to long-duration missions. Furthermore, they can convert in situ resources, such as regolith, into biologically available mineral nutrients and other material building blocks for in situ resource utilization (ISRU) (e.g., Sridhar et al. 2000; Cockell et al. 2020; Kaksonen et al. 2020; Gumulya et al. 2022; Ramalho et al. 2022; Santomartino et al. 2023). It is important to recognize that the interactions of plants and microbes within habitats are inexorably linked, and novel habitats have been shown to impose on the plant–microbe relationship (e.g., Haveman et al. 2022; Schuerger et al. 2022; Koehle et al. 2023). The impact of the ILME on the plant–microbe relationship is unknown and can only be assessed during a Mars surface mission.
Microbial Populations
The impact of the martian environment on the microbial populations associated with the humans and their attending biology comprises the first BPS objective. It is important to determine whether microbial population dynamics and species distribution in biological systems (crew, animal, and plant microbiomes, and BLiSS) and in the habitable volumes (including the physical Environmental Control and Life-Support System [ECLSS]) are stable and promote health and performance throughout the mission. The scientific importance of this objective is tied to the essential role of microbes in terrestrial systems as vital components of most macroorganisms and ecologies. Human-associated microbiomes strongly affect the health of the crew, and the small size of the exploration system makes it vulnerable to instabilities and the propagation of pathogenic species. An irreplaceable loss of a microbial species in the crew microbiome could be severely debilitating, which would, at a minimum, compromise or undermine crew performance and could result in severe health issues in the long term (Blaser and Falkow 2009; Paradiso et al. 2014; de Souza et al. 2020; Douglas et al. 2021; Dubey et al. 2021; Fan and Pedersen 2021; Nishijima et al. 2025). Unmonitored or uncontrolled microbial growth in ECLSS components (e.g., water processing units) may have detrimental effects on the engineering systems and crew health (Godia et al. 2004; Hendrickx et al. 2006; Walker and Granjou 2017; Muirhead et al. 2018; Zea et al. 2018, 2020). Plant microbiomes similarly contribute to plant performance and food safety (e.g., Schuerger et al. 2022; Nadarajah and Rahman 2023) and, thus, have a large impact on mission capability. Experience from the International Space Station and other closed habitats shows that microbiomes are shared across crew members, interior spaces (including the ECLSS), and plants in BLiSS habitats (Voorhies et al. 2019; Avila-Herrera et al. 2020). Thus, a negative impact in one microbial population could propagate throughout a habitat and all members (humans and support systems). It is imperative that microbial systems be studied by the first crew on the surface of Mars, as that is the only means to evaluate the impact of Mars radiation, martian gravity, and the unique vehicle environment on microbiomes. Such studies will also provide insight into the likely composition of forward contamination from the habitable volumes to the martian surface environment.
Plants
Plants are crucial components of BLiSS and have long been viewed as essential features of isolated human habitats for food, recycling, in situ mineral capture, and emotional comfort (e.g., Salisbury 1999; Czupalla et al. 2005; Wheeler 2009; Wheeler 2011; Perchonok et al. 2012; Fu et al. 2016; De Micco et al. 2023). Plant research for exploration environments and BLiSS application is one of the primary research campaigns identified in the 2023 decadal survey, Thriving in Space (NASEM 2023b). The second BPS top objective is to determine the impact of the integrated Mars environment on plant and animal physiology, development, and biomolecular traits to help guide strategies for successfully incorporating plants in BLiSS in martian habitats. Epigenetic traits are important to adaptive strategies in stressful and novel environments (e.g., Paul et al. 2021; Talarico et al. 2024; Ma et al. 2025). The longer-duration campaigns can further address epigenetic changes over generational populations, thereby assessing how the integrated martian environment could impact long-term outposts reliant on plant-based BLiSS for survival. The scientific importance of understanding how the martian environment affects plants in human habitats cannot be overstated. Plants are critical to reduce resupply and support long-term habitation of distant outposts. Although plants will initially be used to augment crew diets with a fresh food component and nutraceuticals, ultimately, plant-centered BLiSS will play a primary role in a providing a reliable source of food, air and water revitalization, nutraceuticals, and essential microbiome fiber (NASEM 2023b). The envisioned reliance on BLiSS in exploration habitats elevates understanding plant and animal physiology on Mars to a top objective. The nature of plant cultivation within BLiSS habitats is also a crucial component of this objective. The two primary approaches for growing plants in exploration habitats are first, using in situ resources such as planetary regolith as a growth substrate, and second, using hydroponic systems to support growth and deliver nutrients. Both systems have pros and cons (e.g., Ming and Henninger 1994; Paradiso et al. 2014; Zabel et al. 2016, 2020; Chinnannan et al. 2023; Fackrell et al. 2024; Goncalves et al. 2024). Although it has been shown that plants can be successfully cultivated in true lunar regolith (Paul et al. 2022), the efficacy of using martian regolith can only be tested with true martian regolith (Eichler et al. 2021); thus, conducting plant growth experiments with the regolith from the landing site is an essential component of the top plant objective. Thriving in Space and the Mars Exploration Program Analysis Group call out ISRU as high-priority objectives for almost all fields of study.
HUMAN FACTORS SCIENCE PRIORITIES
The two top priorities for HF focus on the impact of the ILME on allostatic load in the crew. The impact of allostatic load needs to be considered in terms of physical, emotional, and cognitive health effects on individual crew members, team functioning and cohesion of the crew, and capacity of the crew to perform operational and science return tasks.
Physical and Behavioral Health
Living and working on Mars presents a number of unique physiological and psychological stressors for the multigender, multicultural crew. The ILME includes several unique and interacting features that can affect physical and behavioral health, including modified circadian rhythms owing to the 24.6-hour martian sol (compared to the 24-hour Earth day); isolation and confinement with Earth out of view (Kanas 2020, 2023); and critical ILME variables, such as radiation and dust, also called out by other panels. Because the long-term effects of the ILME on the human body or on crew member behavioral health are not known, occupational surveillance information on any health effects that appear frequently on Mars will be important for all those involved in current or future Mars exploration. If a crew member develops cancer, cognitive difficulties, lung fibrosis, or any other health condition, this cannot be considered solely a private medical matter. Knowing that these conditions occurred will be crucial for planning future Mars missions and protecting future crews. Two implications follow: (1) tracking the frequency and patterns of medical issues that occur on Mars—the epidemiology of health and medical issues—will be a key research goal, and (2) an occupational health approach to medical data will need to be taken to make sure information about these events is clearly shared. Medical data need to be shared between medical operations and the research community to avoid redundant testing, promote cross-collaboration, and ensure that relevant findings are shared (IOM 2001).
Support for Crew Performance
In addition to impacts on physical and behavioral health, aspects of the ILME can significantly degrade crew performance capability (Kanas et al. 2001, 2007), with longitudinal effects that may only be known after exposure to the ILME. Examples include living in a mildly hypobaric and/or hypoxic atmosphere with frequent work tasks in a pressurized suit (Lange et al. 2005; Belobrajdic et al. 2021; Kluis and Diaz-Artiles 2021), extended partial gravity (0.38g) exposure (Petersen et al. 2022; Whittle et al. 2022; Whittle and Diaz-Artiles 2023), potentially after months of microgravity; and significant time delays for Earth communications, ranging from 4 to 20 minutes one way (Caldwell 2005; Caldwell and Wang 2009; Love and Reagan 2013; Kintz and Palinkas 2016; Fischer and Mosier 2020; Fischer et al. 2023) and periodic communications outages when the Sun blocks Earth–Mars communication pathways. Tasks like construction, mining, and sample gathering on Mars in a pressurized suit are hazardous and expose crews to the risks of trauma, decompression sickness, and thermal injury (Buckey 2006). Partial gravity reduces the usual loads on bones, muscles, as well as the central nervous, cardiovascular, and vestibular systems (Clement et al. 2019), with complex impacts on occupational work exposures and potential injuries.
As mentioned above, radiation and dust variables (which are also of interest to other panels) have impacts on crew health and performance, as well as implications for other HESs. Radiation increases cancer risk and produces ongoing central nervous system damage, which can manifest as cognitive impairment (Buckey 2006; Cucinotta et al. 2014; Alaghband et al. 2023; Britten and Limoli 2023). Accurate characterization of the radiation environment on Mars and its biological impact requires precise measurements of radiation fields both inside and outside the habitat. These measurements provide detailed data on the secondary particles generated when high-energy galactic cosmic rays and solar particles interact with the martian surface and any shielding materials, such as habitat walls or regolith. Dust is ubiquitous on Mars and can contact the eyes and skin or be inhaled or ingested, creating unknown health risks (NRC 2002a; Levine et al. 2018; Pohlen et al. 2022; Miranda et al. 2023).
REQUIREMENTS OR ASSUMPTIONS
This panel makes several essential assumptions associated with the impact of the Mars environment. First, human health and performance is tied to the successful completion of all science on the surface on Mars: science return is compromised if astronauts are compromised. Second, no single aspect of the martian environment will act independently on human physiology, human behavior, or the human capability to work in that environment (the ILME concept). Third, no single aspect of the martian environment will act independently on the responses of the attending biology, from internal microbiomes to the plants and animals that are brought for experimental evaluations. Fourth, while measurements can be made to assay primary targets of specific environmental stressors (e.g., from dust, radiation, and reduced gravity), overall, the ILME is outside the evolutionary experience of terrestrial biology and will influence all responses of terrestrial biology to that environment. Last, it is important that physiological and behavioral health data be shared between medical operations and the research community to avoid redundancy in testing, to promote cross-collaboration, and to ensure that relevant findings with impacts to human health, safety, and science return are disseminated. Ongoing and open access to astronaut health monitoring data, with appropriate approvals, will inform and enhance the ability to conduct HF and BPS science objectives and will be crucial to making decisions for future mission objectives.
CAVEATS AND MEASUREMENT OPTIONS
One important BPS/HF consideration is the need to perform measurements longitudinally, and in many cases continuously, to determine dose–response effects of the ILME on biological, physiological, and behavioral health processes. This will result in sample collection that would be impractical to return to Earth for processing. If sample analysis reveals actionable results, having access to immediate processing capabilities will be required. It will be important to develop medical technologies for in situ, noninvasive, real-time analysis of biological samples from multiple species (including human physiological and behavioral samples) that also minimizes use of crew time for repetitive tasks—for example, technology to remotely monitor crew interactions or assess crew cohesion, or provide precise measurements of the radiation field on Mars (crucial for correlating environmental exposure with biological effects observed in biodosimetry).
Dosimeters, such as thermoluminescent detectors, optically stimulated luminescence dosimeters, and active silicon-based radiation detectors, need to be deployed to measure the dose, dose rate, and composition of the radiation field, including galactic cosmic rays and solar particle events. These instruments can be positioned on the surface, in habitats, and on the human body (e.g., personal dosimeters) to capture spatial and temporal variations in exposure. Detailed spectral analysis of the radiation field will aid in identifying high-LET (linear energy transfer) particles, which cause more severe biological damage. These environmental measurements can then be directly correlated with biodosimetry data by establishing a link between specific radiation doses and types and observed biomarkers of DNA damage, oxidative stress, and inflammation.
No specific set of biomarkers or clinical criteria have been established as an accurate indicator of allostatic load (Pfaltz and Schnyder 2023). This panel describes a suite of biomedical testing meant to interrogate all relevant physiological and psychological systems. It is expected that medical technology will evolve significantly prior to the first human mission to Mars; however, understanding the complex relationships between the ILME and biological and physiological behaviors is limited, and requires significant scientific and analytical development.
There are other crucial aspects of human physiology and behavior impacted by the ILME that are beyond the scope of the panel’s emphasis, such as sexual behavior (IOM and NRC 2006), demographic or other characteristics of the crew or crew composition, and other cultural or ethical considerations (Gangeme et al. 2023).
Nonetheless, the top HF priorities emphasize addressing crew physiological and behavioral health, including topics such as reproductive physiology, response to radiation and other ILME factors, and psychosocial dynamics of crew behavior and performance (Caldwell 2015; Kanas 2023). Ideally, measurement of allostatic load will include a number of standard measures that have been used in previous space and simulation studies to facilitate comparison of data across various reference missions (low Earth orbit, Moon orbit, Moon base, and Mars expedition).
TECHNOLOGY ADVANCEMENT IMPACTS
The desire for increasing density and range of longitudinal data collection requires attention to technology support for continuous, longitudinal (as well as unobtrusive and minimally impacting on crew) physiological measurement (e.g., clothing-based monitoring; biomarker assessment via interstitial fluids, noncontact temperature measures, or smart toilets). These capabilities, embedded in the habitat, crew garments, and life-support technologies, expand the range of early-stage assessments for chronic disease etiology and progression, although additional measures come with the risk of spurious or happenstance results.
One potentially transformative technology suite to support science priorities includes intelligent agent capability to extrapolate and support dynamic scientific data collection and evolving or generative hypothesis testing based on real-time, local analysis results (see Caldwell 2015), enhancing science return across multiple panels.
Continued advancement in a variety of biomolecular tools, such as nucleic acid sequencers, mass spectrometers for proteins and metabolites, spatial transcriptomics, and other biomarker assays, is expected. Advancements in computational capabilities will also enhance the ability to conduct sophisticated bioinformatic and other computational analyses on the surface.
