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All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

The Search for Organic Compounds of Martian Origin in Gale Crater by the Sample Analysis at Mars (SAM) Instrument on Curiosity

One of the key objectives of the Mars Science Laboratory rover and the Sample Analysis at Mars (SAM) instrument suite is to determine the inventory of organic and inorganic volatiles in the atmosphere and surface regolith and rocks to help assess the habitability potential of Gale Crater. The SAM instrument on the Curiosity rover can detect volatile organic compounds thermally evolved from solid samples using a combination of evolved gas analysis (EGA) and gas chromatography mass spectrometry (GCMS) (Mahaffy et al. 2012). The first solid samples analyzed by SAM, a scoop of windblown dust and sand at Rocknest, revealed several chloromethanes and a C4-chlorinated hydrocarbon derived primarily from reactions between a martian oxychlorine phase (e.g. perchlorate) and terrestrial carbon from N-methyl-N-(tertbutyldimethylsilyl)- trifluoroacetamide (MTBSTFA) vapor present in the SAM instrument background (Glavin et al. 2013). After the analyses at Rocknest, Curiosity traveled to Yellowknife Bay and drilled two separate holes in a fluvio-lacustrine sediment (the Sheepbed unit) designated John Klein and Cumberland. Analyses of the drilled materials by both SAM and the CheMin X-Ray Diffraction instrument revealed a mudstone consisting of ~20 wt% smectite clays (Ming et al. 2013; Vaniman et al. 2013), which on Earth are known to aid the concentration and preservation of organic matter. Oxychlorine compounds were also detected in the Sheepbed mudstone during pyrolysis; however, in contrast to Rocknest, much higher levels of chloromethanes were released from the Sheepbed materials, suggesting an additional, possibly martian source of organic carbon (Ming et al. 2013). In addition, elevated abundances of chlorobenzene and a more diverse suite of chlorinated alkanes including dichloropropane and dichlorobutane detected in Cumberland compared to Rocknest suggest that martian or meteoritic organic carbon sources may be preserved in the mudstone (Freissinet et al. 2013). Chloromethane and dichloromethane were also identified after thermal volatilization of the surface soils by the GCMS instruments at the Viking landing sites, although no other chlorinated hydrocarbons were reported (Biemann et al. 1977). Here we focus on the origin of the chlorinated hydrocarbons detected in the Sheepbed mudstone by SAM and the implications for the preservation of organic matter in near-surface materials on Mars.

Mars Curiosity Rover↗
NASA NTRS2016

Mineralogical and Geochemical Trends in a Fluviolacustrine Sequence in Gale Crater, Mars

The Mars Science Laboratory rover, Curiosity, landed at Gale crater in August 2012 and has been investigating a sequence of dominantly fluviolacustrine sediments deposited 3.6-3.2 billion years ago. Curiosity collects quantitative mineralogical data with the CheMin XRD/XRF instrument and quantitative chemical data with the APXS and ChemCam instruments. These datasets show stratigraphic mineralogical and geochemical variability that suggest a complex aqueous history. The Murray Formation, primarily composed of fine-laminated mudstone, has been studied in detail since the arrival at the Pahrump Hills in September 2014. CheMin data from four samples show variable amounts of iron oxides, phyllosilicates, sulfates, amorphous and crystalline silica, and mafic silicate minerals. Geochemical data throughout the section show that there is significant variability in Zn, Ni, and Mn concentrations. Mineralogical and geochemical trends with stratigraphy suggest one of possibly several aqueous episodes involved alteration in an open system under acidic pH, though other working hypotheses may explain these and other trends. Data from the Murray Formation contrast with those collected from the Sheepbed mudstone located approximately 60 meters below the base of the Murray Formation, which showed evidence for diagenesis in a closed system at circumneutral pH. Ca-sulfates filled late-stage veins in both mudstones.

Rampe, E.↗
NASA NTRS2016

Modeling of Sulfide Microenvironments on Mars

Yellowknife Bay (YKB; sol 124-198) is the second site that the Mars Science Laboratory Rover Curiosity investigated in detail on its mission in Gale Crater. YKB represents lake bed sediments from an overall neutral pH, low salinity environment, with a mineralogical composition which includes Ca-sulfates, Fe oxide/hydroxides, Fe-sulfides, amorphous material, and trioctahedral phyllosilicates. We investigate whether sulfide alteration could be associated with ancient habitable microenvironments in the Gale mudstones. Some textural evidence for such alteration may be pre-sent in the nodules present in the mudstone.

Schwenzer, S. P.↗
NASA NTRS2016

Diagenesis Along Fractures in an Eolian Sandstone, Gale Crater, Mars

The Mars Science Laboratory rover Curiosity has been exploring sedimentary deposits in Gale crater since August 2012. The rover has traversed up section through approx.100 m of sedimentary rocks deposited in fluvial, deltaic, lacustrine, and eolian environments (Bradbury group and overlying Mount Sharp group). The Stimson formation lies unconformable over a lacustrine mudstone at the base of the Mount Sharp group and has been interpreted to be a cross-bedded sandstone of lithified eolian dunes. Mineralogy of the unaltered Stimson sandstone consists of plagioclase feldspar, pyroxenes, and magnetite with minor abundances of hematite, and Ca-sulfates (anhydrite, bassanite). Unaltered sandstone has a composition similar to the average Mars crustal composition. Alteration "halos" occur adjacent to fractures in the Stimson. Fluids passing through these fractures have altered the chemistry and mineralogy of the sandstone. Silicon and S enrichments and depletions in Al, Fe, Mg, Na, K, Ni and Mn suggest aqueous alteration in an open hydrologic system. Mineralogy of the altered Stimson is dominated by Ca-sulfates, Si-rich X-ray amorphous materials along with plagioclase feldspar, magnetite, and pyroxenes, but less abundant in the altered compared to the unaltered Stimson sandstone and lower pyroxene/plagioclase feldspar. The mineralogy and geochemistry of the altered sandstone suggest a complicated history with several (many?) episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline).

Ming, D. W.↗
NASA NTRS2016

Elemental Gains/Losses Associated with Alteration Fractures in an Eolian Sandstone, Gale Crater, Mars

The Mars Science Laboratory rover Curiosity has traversed up section through approximately 100 m of sedimentary rocks deposited in fluvial, deltaic, lacustrine, and eolian environments (Bradbury group and overlying Mount Sharp group). The Stimson formation unconformably overlies a lacustrine mudstone at the base of the Mount Sharp group and has been interpreted to be a cross-bedded sandstone of lithified eolian dunes. Unaltered Stimson sandstone has a basaltic composition similar to the average Mars crustal composition, but is more variable and ranges to lower K and higher Al. Fluids passing through alteration "halos" adjacent to fractures have altered the chemistry and mineralogy of the sandstone. Elemental mass gains and losses in the alteration halos were quantified using immobile element concentrations, i.e., Ti (taus). Alteration halos have elemental gains in Si, Ca, S, and P and large losses in Al, Fe, Mn, Mg, Na, K, Ni, and Zn. Mineralogy of the altered Stimson is dominated by Ca-sulfates, Si-rich X-ray amorphous materials along with plagioclase feldspar, magnetite, and pyroxenes. The igneous phases were less abundant in the altered sandstone with a lower pyroxene/plagioclase feldspar. Large elemental losses suggest acidic fluids initially removed these elements (Al mobile under acid conditions). Enrichments in Si, Ca, and S suggest secondary fluids (possibly alkaline) passed through these fractures leaving behind X-ray amorphous Si and Ca-sulfates. The mechanism for the large elemental gains in P is unclear. The geochemistry and mineralogy of the altered sandstone suggests a complicated diagenetic history with multiple episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline).

Ming, D. W.↗
NASA NTRS2016

Soil Crystallinity As a Climate Indicator: Field Experiments on Earth and Mars

Soil crystallinity is largely determined by leaching rates, as high leaching rates favor the rapid precipitation of short order or poorly-crystalline phases like the aluminosilicate allophane. High leaching rates can occur due to high precipitation rates, seasonal monsoons, or weathering of glass, but are also caused by the rapid onset of seasonal melting of snow and ice in cold environments. Thus, cold climate soils are commonly dominated by poorly crystalline phases, which mature into kaolin minerals over time. Thus, we hypothesize that, in some contexts, soils with high abundances of poorly crystalline phases could indicate formation under cold climatic conditions. This model could be helpful in interpreting the poorly-constrained paleoclimate of ancient Mars, as the crystallinity of ancient soils and soil-derived sediments appears to be highly variable in time and space. While strong signatures of crystalline phyllosilicates have been identified in possible ancient paleosols on Mars, Mars Science Laboratory rover investigations of diverse ancient sediments at Gale Crater has shown that they can contain very high abundances (40-50 wt%) of poorly crystalline phases. We hypothesize that these poorly crystalline phases could be the result of weathering by ice/snow melt, perhaps providing support for sustained cold climates on early Mars punctuated by more limited warm climates. Furthermore, such poorly crystalline soils could be highly fertile growth media for future human exploration and colonization on Mars. To test this hypothesis, we are currently using rover-like instrumentation to investigate the mineralogy and chemistry of weathering products generated by snow and ice melt in a Mars analog alpine environment: the glaciated Three Sisters volcanic complex in central Oregon. Alteration in this glacial environment generates high abundances of poorly crystalline phases, many of which have compositions distinct from those identified in previous terrestrial investigations, and perhaps more similar to poorly crystalline phases identified on Mars.

Horgan, Briony↗
NASA NTRS2016

P21C-2113: Constraining Hesperian Martian PCO2 from Mineral Analysis at Gale Crater

Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with widespread evidence of liquid water at the planet's surface in the Noachian and Early Hesperian. Current estimates of ancient martian CO levels, derived from global inventories of carbon, and orbital detections of Noachian and Early Hesperian clay mineralbearing terrains indicate CO levels that are unable to support warm and wet conditions. These estimates are subject to various sources of uncertainty however. Mineral and contextual sedimentary environmental data collected by the Mars Science Laboratory rover Curiosity in Gale Crater provide a more direct means of estimating the atmospheric partial pressure of CO (P ) coinciding with a long-lived lake system in Gale crater at approximately 3.5 Ga. Results from a reaction transport model, which simulates mineralogy observed within the Sheepbed member at Yellowknife Bay by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicate atmospheric levels in the 10's mbar range. At such low P levels, climate models are unable to warm Hesperian Mars anywhere near the freezing point of water and other gases are required to raise atmospheric pressure to prevent lakes from boiling away. Thus, lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climate models lack an essential component that would serve to elevate surface temperatures, at least temporally and/or locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO in inferred warmer conditions of the Noachian.

Bristow, Thomas↗
NASA NTRS2017

Calcium Sulfates at Gale Crater and Limitations on Gypsum Stability

The Mars Science Laboratory rover has been exploring sedimentary rocks of the Bradbury group and overlying Murray formation, as well as the unconformably overlying Stimson formation. Early in exploration, and continuing to present, there have been observations of many Ca-sulfate veins that cut all three stratigraphic units. The CheMin XRD instrument on Curiosity provides complete mineralogy for drilled or scooped samples, with explicit identification of gypsum, bassanite, and anhydrite (crystal structure of so-called "soluble anhydrite," or gamma-CaSO4, is so similar to bassanite that it can't be distinguished at CheMin 2-theta resolution; here we refer to these similar dehydrated forms simply as bassanite).

Vantiman, D. T.↗
NASA NTRS2016

Thermophysical Properties Along Curiosity's Traverse in Gale Crater, Mars, Derived from the REMS Ground Temperature Sensor

The REMS instrument onboard the Mars Science Laboratory rover, Curiosity, has measured ground temperature nearly continuously at hourly intervals for two Mars years. Coverage of the entire diurnal cycle at 1 Hz is available every few martian days. We compare these measurements with predictions of surface atmosphere thermal models to derive the apparent thermal inertia and thermally derived albedo along the rovers traverse after accounting for the radiative effects of atmospheric water ice during fall and winter, as is necessary to match the measured seasonal trend. The REMS measurements can distinguish between active sand, other loose materials, mudstone, and sandstone based on their thermophysical properties. However, the apparent thermal inertias of bedrock dominated surfaces [approx. 350-550 J m(exp. -2) K(exp. -1 s(exp. -1/2 )] are lower than expected. We use rover imagery and the detailed shape of the diurnal ground temperature curve to explore whether lateral or vertical heterogeneity in the surface materials within the sensor footprint might explain the low inertias. We find that the bedrock component of the surface can have a thermal inertia as high as 650-1700 J m(exp. -2) K(exp. -1) s(exp. -1/2) for mudstone sites and approx. 700 J m(exp. -2) K(exp. -1) s(exp. - 1/2) for sandstone sites in models runs that include lateral and vertical mixing. Although the results of our forward modeling approach may be non-unique, they demonstrate the potential to extract information about lateral and vertical variations in thermophysical properties from temporally resolved measurements of ground temperature.

Vasavada, Ashwin R.↗
NASA NTRS2015

Parallel Study of HEND, RAD, and DAN Instrument Response to Martian Radiation and Surface Conditions

Nuclear detection methods are being used to understand the radiation environment at Mars. JPL (Jet Propulsion Laboratory) assets on Mars include: Orbiter -2001 Mars Odyssey [High Energy Neutron Detector (HEND)]; Mars Science Laboratory Rover -Curiosity [(Radiation Assessment Detector (RAD); Dynamic Albedo Neutron (DAN))]. Spacecraft have instruments able to detect ionizing and non-ionizing radiation. Instrument response on orbit and on the surface of Mars to space weather and local conditions [is discussed] - Data available at NASA-PDS (Planetary Data System).

Mars↗
NASA NTRS2017

The Amorphous Composition of Three Mudstone Samples from Gale Crater: Implications for Weathering and Diagenetic Processes on Mars

The Mars Science Laboratory rover, Curiosity, is exploring the lowermost formation of Gale crater's central mound. Within this formation, three samples named Marimba, Quela, and Sebina have been analyzed by the CheMin X-ray diffractometer and the Alpha Particle X-ray Spectrometer (APXS) to determine mineralogy and bulk elemental chemistry, respectively. Marimba and Quela were also analyzed by the SAM (Sample Analysis at Mars) instrument to characterize the type and abundance of volatile phases detected in evolved gas analyses (EGA). CheMin data show similar proportions of plagioclase, hematite, and Ca-sulfates along with a mixture of di- and trioctahedral smectites at abundances of approximately 28, approximately 16, and approximately 18 wt% for Marimba, Quela, and Sebina. Approximately 50 wt% of each mudstone is comprised of X-ray amorphous and trace crystalline phases present below the CheMin detection limit (approximately 1 wt%). APXS measurements reveal a distinct bulk elemental chemistry that cannot be attributed to the clay mineral variation alone indicating a variable amorphous phase assemblage exists among the three mudstones. To explore the amorphous component, the calculated amorphous composition and SAM EGA results are used to identify amorphous phases unique to each mudstone. For example, the amorphous fraction of Marimba has twice the FeO wt% compared to Quela and Sebina yet, SAM EGA data show no evidence for Fe-sulfates. These data imply that Fe must reside in alternate Fe-bearing amorphous phases (e.g., nanophase iron oxides, ferrihydrite, etc.). Constraining the composition, abundances, and proposed identity of the amorphous fraction provides an opportunity to speculate on the past physical, chemical, and/or diagenetic processes which produced such phases in addition to sediment sources, lake chemistry, and the broader geologic history of Gale crater.

Achilles, C. N.↗
NASA NTRS2018

Amorphous Phase Characterization Through X-Ray Diffraction Profile Modeling: Implications for Amorphous Phases in Gale Crater Rocks and Soils

The CheMin X-ray diffraction instrument on the Mars Science Laboratory rover has analyzed 18 rock and soil samples in Gale crater. Diffraction data allow for the identification of major crystalline phases based on the positions and intensities of well-defined peaks and also provides information regarding amorphous and poorly-ordered materials based on the shape and positions of broad scattering humps. The combination of diffraction data, elemental chemistry from APXS (Alpha Particle X-ray Spectrometer) and evolved gas analyses (EGA) from SAM (Sample Analysis at Mars) help constrain possible amorphous materials present in each sample (e.g., glass, opal, iron oxides, sulfates) but are model dependent. We present a novel method to characterize amorphous material in diffraction data and, through this approach, aim to characterize the phases collectively producing the amorphous profiles in CheMin diffraction data. This method may be applied to any diffraction data from samples containing X-ray amorphous materials, not just CheMin datasets, but we re-strict our discussion to Martian-relevant amorphous phases and diffraction data measured by CheMin or CheMin-like instruments.

Achilles, C. N.↗
NASA NTRS2016

Constraining Hesperian martian PCO2 from mineral analysis at Gale crater

Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planet-wide evidence of liquid water at the planets surface in the Noachian and Early Hesperian. Current estimates of ancient martian CO2 levels, derived from global inventories of carbon, and orbital detections of Noachian and Early Hesperian clay mineral-bearing terrains indicate CO2 levels that are unable to support warm and wet conditions. These estimates are subject to various sources of uncertainty however. Mineral and contextual sedimentary environmental data collected by the Mars Science Laboratory rover Curiosity in Gale Crater provide a more direct means of estimating the atmospheric partial pressure of CO2 (PCO2) coinciding with a long-lived lake system in Gale crater at ~3.5 Ga. Results from a reaction-transport model, which simulates mineralogy observed within the Sheepbed member at Yellowknife Bay by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicate atmospheric PCO2 levels in the 10’s mbar range. At such low PCO2 levels, climate models are unable to warm Hesperian Mars anywhere near the freezing point of water and other gases are required to raise atmospheric pressure to prevent lakes from boiling away. Thus, lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climate models still lack an essential component that would serve to elevate surface temperatures, at least temporally and/or locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO2 in inferred warmer conditions of the Noachian.

Bristow, T. F.↗
NASA NTRS2019

Constraints on Martian Ancient Magmatic Processes Using Mineral Chemistry of Sedimentary Rocks in Gale Crater, Mars

If Mars has been assumed to be mostly basaltic for a long time, a series of recent discoveries have challenged this simplistic view. Orbital data indicated feldspar-rich rocks in Noachian terrains, likely supporting ancient evolved magmatism. The first indurated regolithic martian meteorite breccia NWA 7034, dated at 4.43 Gyr, contain several leucocratic felsic clasts identified as monzonitic and trachyandesitic, containing feldspars including K-spars and Na-rich plagioclases, pyroxenes, ilmenites and apatites. These clasts have been interpreted as the result of crystallization of a large impact pond. The Mars Science Laboratory rover (Curiosity), travelling within sedimentary bedrock on the floor of the Gale impact crater, discovered feldspar cumulates and a trachyandesite suggesting fractional crystallization of a basaltic melt. In addition, in the Bradbury group of fluvio-deltaic rocks (observed during the 1st 750 sols), sedimentary rocks are mostly comprised of secondary phases and detrital igneous minerals like feldspar, and pyroxene that are thought to come from Noachian-aged magmatic sources, although no definite origin and igneous processes have been inferred.

Payr, V.↗
NASA NTRS2021

Gravity Wave Observations by the Mars Science Laboratory REMS Pressure Sensor and Comparison with Mesoscale Atmospheric Modeling with MarsWRF

Surface pressure measurements on Mars have revealed a wide variety of atmospheric phenomena. The Mars Science Laboratory Rover Environmental Monitoring Station pressure sensor dataset is now the longest duration record of surface pressure on Mars. We use the first 2580 martian sols, nearly 4 Mars years,of measurements to identify atmospheric pressure waves with periods of tens of minutes to hours using wavelet analysis on residual pressure after the tidal harmonics are removed. We find these waves have a clear diurnal cycle with strongest activity in the early morning and late evening and a seasonal cycle with the strongest waves in the second half of the martian year (Ls= 180-360°). The strongest such waves of the entire mission occurred during the Mars Year 34 global dust storm. Comparable atmospheric waves are identified using atmospheric modeling with the MarsWRF general circulation model in a “nested” high spatial resolution mode. With the support of the modeling, we find these waves best fit the expected properties of inertia-gravity waves with horizontal wavelengths of O(100s) of km. PLAIN LANGUAGE SUMMARY Measuring air pressure from the surface of Mars has revealed a wide variety of atmospheric phenomena. The Curiosity rover's record or surface air pressure is now the longest yet made on Mars.We use the first ~8 years of Curiosity's pressure observations to look for atmospheric waves with periods of tens of minutes to hours. We find these waves have a clear pattern in their daily behavior with the strongest activity in the early morning and late evening and a seasonal cycle with the strongest waves in the second half of the martian year (Northern hemisphere fall and winter). The strongest such waves occurred in 2018 during a global dust storm. We find comparable waves in atmospheric modeling. With the support of modeling, we find these waves best fit the expected properties of buoyancy waves forced by airflow over topography with horizontal wavelengths of 100-1000 km.

Scott D Guzewich↗
NASA NTRSDate not supplied

The CheMin X-ray Diffractometer on MSL Curiosity: A Decade of Mineralogical Observations from Gale Crater, Mars

For more than a decade, the CheMin X-ray Diffraction instrument on the Mars Science Laboratory rover Curiosity has been returning quantitative mineralogical data from Gale crater, Mars. CheMin receives and analyzes sieved soil and powdered rock samples from Curiosity’s Sample Acquisition / Sample Processing and Handling (SA/SPaH) system. To date, 38 samples have been analyzed over the course of a 28 km transit. These samples document more than 600 vertical meters of flat-lying lacustrine, fluvial and aeolian sediments that comprise the lower part of the central mound of Gale crater (commonly called Mt. Sharp).The principal mineralogy of the sediments is basaltic, with evidence of early and late-stage diagenetic overprinting. The rocks in many cases preserve most of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed. Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that in many cases the diagenetic changes observed are principally isochemical. Exceptions to this include secondary nodules, calcium sulfate veining and rare alteration halos. A striking hematite-rich feature in lower Mt. Sharp called Vera Rubin Ridge is interpreted to be lake sediment diagenetically altered by silica-poor fluids. A surprising and as yet poorly understood observation is that nearly all of the 3.7 Gyr old sedimentary rocks analyzed to date are comprised of 25-50% X-ray amorphous material. Overall, this 600 m vertical section of sedimentary rock explored in lower Mt. Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments. The mineralogical changes observed going up-section include a transition from trioctahedral to dioctahedral clay minerals and a transition from magnetite to hematite. More recently, in the last 150 m of section, CheMin has documented an overall decrease in clay minerals and increase in Fe3+ oxides and oxyhydroxides. The mineralogical changes observed in Gale crater may document the gradual drying out and oxidation of the martian hydrosphere.

CHEMIN↗
NASA NTRSDate not supplied

MastCam Multispectral Examination of Rocks in the Sulfate-Bearing Terrain of Marker Band Valley, Gale Crater, Mars

A primary objective of the 4th extended mission of the Mars Science Laboratory rover Curiosity is to characterize the sulfate-bearing beds exposed on the slopes of Mt. Sharp (Aeolis Mons) above the clay-bearing beds of the Glen Torridon region characterized in the 3rd extended mission. Orbital reflectance spectroscopy from CRISM has indicated the presence of polyhydrated Mg sulfates in the portion of Mt. Sharp dubbed “Marker Band Valley” (MBV). The Marker Band is a darker toned, high-Ca pyroxene bearing unit that extends around much of Mt. Sharp above the first exposures of sulfate-bearing beds. Standoff imaging of the Marker Band indicates that it is not monolithic, but contains at least two subunits. Curiosity measures multispectral reflectance in the 430 to 1012 nm range with its Mastcam. While diagnostic spectral features of Mg-sulfates are not present in the Mastcam spectral range, a water overtone feature of some polyhydrated sulfates can be observed as a drop in reflectance in the longest wavelength one to three bands of Mastcam multispectral data. Other minerals associated with sulfate-generating alteration processes, most notably Fe-bearing minerals, are more readily detectable in Mastcam multispectral data.

W H Farrand↗
NASA NTRS2022

A Primordial Atmospheric Origin of Hydrospheric Deuterium Enrichment on Mars

The deuterium-to-hydrogen (D/H or 2H/1H) ratio of Martian atmospheric water (~6× standard mean ocean water, SMOW) is higher than that of known sources, requiring planetary enrichment. A recent measurement by NASA’s Mars Science Laboratory rover Curiosity of Hesperian-era (>3 Ga) clays yields a D/H ratio ~3×SMOW, demonstrating that most of the enrichment occurs early in Mars’s history, reinforcing the conclusions of Martian meteorite studies. As on Venus, Mars’s D/H enrichment is widely thought to reflect preferential loss to space of 1H (protium) relative to 2H (deuterium), but both the cause and the global environmental context of large and early hydrogen losses remain to be determined. Here, we apply a recent model of primordial atmosphere evolution to Mars, link the magma ocean of the accretion epoch with a subsequent water-ocean epoch, and calculate the behavior of deuterium for comparison with the observed record. In contrast to earlier works that consider Martian D/H fractionation in atmospheres in which hydrogen reservoirs are present exclusively as H2O or H2, here we consider 2-component (H2O-H2) outgassed atmospheres in which both condensed (H2O) and escaping (H2) components – and their interaction – are explicitly calculated. We find that a a ≈2-3× hydrospheric deuterium-enrichment is produced rapidly if the Martian magma ocean is chemically reducing at last equilibration with the primordial atmosphere, making H2 and CO the initially dominant species, with minor abundances of H2O and CO2. Reducing gases – in particular H2 – can cause substantial greenhouse warming and prevent a water ocean from freezing immediately after the magma ocean epoch. We find that greenhouse warming due to plausible H2 inventories (pH2=1-102 bars) yields surface temperatures high enough (Ts=290-560 K) to stabilize a water ocean and produce an early hydrological cycle through which surface water can be circulated. Moreover, the pressure-temperature conditions are high enough to produce ocean-atmosphere H2O-H2 isotopic equilibrium through gas-phase deuterium exchange such that surface H2O strongly concentrates deuterium relative to H2, which preferentially takes up protium and escapes from the primordial atmosphere. The efficient physical separation of deuterium-rich (H2O) and deuterium-poor (H2) species via condensation permits equilibrium isotopic partitioning and early atmospheric escape to be recorded in modern crustal reservoirs. The proposed scenario of primordial H2-CO-rich outgassing and escape suggests significant durations (>Myr) of chemical conditions on the Martian surface conducive to prebiotic chemistry immediately following magma ocean crystallization.

Mars↗