Radiolysis of Macromolecular Organic Material in Mars‐Relevant Mineral Matrices

Fox, A. C.; Eigenbrode, J. L.; Freeman, Katherine H.

doi:10.1029/2019je006072

Cited by 36 publications

(50 citation statements)

References 46 publications

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“…As a Noachian‐Hesperian clay‐rich fluviolacustrine siliciclastic system, the Jezero delta deposits represent a promising astrobiological target (McMahon et al, ), provided that putative Martian life colonized surface or near‐subsurface environments. Contingent that putative life survived possibly prolonged dry spells and that organics were protected from galactic cosmic rays by a thicker atmosphere throughout the formation of the Jezero delta (Fox et al, ; McMahon et al, ), our findings corroborate the hypothesis that the distal deposits of Jezero may have preserved evidence of past Martian life. Our estimated “instantaneous” lateral migration rates for the Jezero rivers imply an “instantaneous” bed aggradation rate of

italicAr \approx 5_{- 2}^{+ 5}

m/year, or

italicAr \approx {1.5}_{- 0.5}^{+ 1.5}

cm/sol.…”

Section: Discussionsupporting

confidence: 82%

The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

Lapôtre

Ielpi

2020

AGU Advances

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Although there is little doubt that rivers once flowed on Mars' surface, how sustained and frequent their flows were remains enigmatic. Understanding the hydrology of early Mars, nonetheless, is a prerequisite to resolving the planet's climate history and the astrobiological potential of various ancient putative ecosystems. In 2021, NASA's Perseverance rover will attempt to land near ancient fluviodeltaic deposits in Jezero crater. Deltas offer enhanced organic-matter burial and preservation on Earth but translating this notion to early Martian environments remains speculative in the absence of information on flow intermittency and sedimentation rates. Here we develop a new model to infer the lateral migration rate of Martian river meanders, which, combined with orbiter-based observations of the fluviodeltaic deposits at Jezero crater, allows us to determine a minimum timescale for the formation of its delta. We then independently constrain the total duration of delta formation, including dry spells. Our best estimates suggest that delta formation spanned~19-37 years over a total duration of~380,000 years, i.e., that rivers flowed for a minimum~1 sol/15-30 Martian years and conceivably more frequently, but uncertainties on total duration are large. Despite a possibly arid climate, predicted sedimentation rates are high, suggesting a rapid burial of putative organics in distal deposits. Altogether, our results support Jezero crater's potential as a prime target to look for ancient Martian life and acquire samples to return to Earth. Any discrepancies between our predictions of the deposits' grain-to-bedform-scale architecture and future rover observations will shed critical light onto Mars' early surface environments. Plain Language Summary Rivers once flowed on Mars, but how often, and for how long? Answering these questions will increase our understanding of Mars' habitability at a time when life was already evolving on Earth. NASA's Perseverance rover will land by the remnants of an ancient river delta in Jezero crater. Here we develop a new model to calculate the pace of shifting Martian rivers, which, when applied to orbital observations of the Jezero delta, allows us to determine a minimum duration for delta formation. Combined with an independent estimate for the total duration of delta formation (including dry spells), our results suggest that the delta took a few decades to form over a total timespan of, most likely, hundreds of thousands of years. This result suggests that Mars was likely arid at the time, with rivers flowing for at least 1 Martian day every 15-30 Martian years, and possibly more often. Nonetheless, we predict that sediments would have been buried quickly in the delta, favoring the long-term preservation of possible organic matter. Altogether, our results confirm that Jezero crater is a prime location to understand Mars' early climate, look for traces of ancient Martian life, and return samples from for further analysis on Earth.

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italicAr \approx 5_{- 2}^{+ 5}

m/year, or

italicAr \approx {1.5}_{- 0.5}^{+ 1.5}

cm/sol.…”

Section: Discussionsupporting

confidence: 82%

The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

Lapôtre

Ielpi

2020

AGU Advances

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“…CO 2 evolved at less than ~400°C temperatures from previous samples, coincident with CO, was also generally attributed to these oxidized carbon phases (Sutter et al, 2017, and references therein), and some of these phases such as Mg and Ca oxalates can also evolve CO 2 and CO at temperatures above 400°C (Gadalla, 1984). These types of organic compounds are expected to be present on the Martian surface as a result of oxidation or irradiation of more reduced organic compounds, which are either delivered by meteoritic infall or endogenous to Mars (Benner et al, 2000; Fox et al, 2019). These oxidized carbon compounds could also be present, as is, in meteoritic material that falls to the surface of Mars (Flynn, 1996).…”

Section: Results and Interpretationmentioning

confidence: 99%

Constraints on the Mineralogy and Geochemistry of Vera Rubin Ridge, Gale Crater, Mars, From Mars Science Laboratory Sample Analysis at Mars Evolved Gas Analyses

et al. 2020

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Vera Rubin ridge (VRR) is a topographic high within the layers of Mount Sharp, Gale crater, that exhibits a strong hematite spectral signature from orbit. The Mars Science Laboratory Curiosity rover carried out a comprehensive investigation to understand the depositional and diagenetic processes recorded in the rocks of VRR. Sample Analysis at Mars (SAM) evolved gas analyses (EGA) were performed on three samples from the ridge and one from directly beneath the ridge. SAM evolved H 2 O data suggested the presence of an Fe-rich dioctahedral smectite, such as nontronite, in the sample from beneath the ridge. H 2 O data are also consistent with ferripyrophyllite in VRR samples. SAM SO 2 data indicated that all samples contained Mg sulfates and some Fe sulfate. Several volatile detections suggested trace reduced sulfur sources, such as Fe sulfides and/or S-bearing organic compounds, in two samples while significant O 2 and NO evolved from one sample indicated the presence of oxychlorine and nitrate/nitrite salts, respectively. The O 2 evolution was the second highest to date and the first observed in~1,200 sols. HCl released from all samples likely resulted, in part, from trace chloride salts. All samples evolved CO 2 and CO consistent with oxidized carbon compounds (e.g., oxalates), while some CO 2 may result from carbonate. SAM-derived constraints on the mineralogy and chemistry of VRR materials, in the context of additional mineralogy, geochemistry, and sedimentology information obtained by Curiosity, support a complex diagenetic history that involved fluids of a range of possible salinities, redox characteristics, pHs, and temperatures. Plain Language Summary The Mars Science Laboratory Curiosity rover conducted a detailed study of the rocks that make up the Vera Rubin ridge (VRR) feature in Gale crater, Mars, to better understand Martian geologic history. The Curiosity rover's Sample Analysis at Mars (SAM), a suite of scientific instruments on the rover, measured several diagnostic gases when it was used to heat samples from on and beneath VRR. These gases provided information about the mineralogy and chemistry of VRR samples that, together with additional information from other instruments on the rover, indicated that several different types of fluids affected the rocks in the ridge over geologic time. These fluids varied in temperature, salt content, and acidity.

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“…Fox et al (2019) have used laboratory radiation on Martian analog materials to simulate the effect of cosmic rays and the solar wind on organic material at the surface or subsurface of Mars. Fox et al (2019) examined the effects of cosmic rays by exposing model combinations of organic matter and selected mineral matrices to radiation doses equivalent to geological time scales on Mars. By varying both the mineral matrices and the source of the organic material, they drew conclusions about the role of these rays in the destruction of organic material on Mars.…”

Section: Commentarymentioning

confidence: 99%

“…Fox et al () examined the effects of cosmic rays by exposing model combinations of organic matter and selected mineral matrices to radiation doses equivalent to geological time scales on Mars. By varying both the mineral matrices and the source of the organic material, they drew conclusions about the role of these rays in the destruction of organic material on Mars.…”

Section: Commentarymentioning

confidence: 99%

New Paths for Survivability of Organic Material in the Martian Subsurface

Montgomery

2020

JGR Planets

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Recent space missions have identified organics, chlorinated and non‐chlorinated, on Mars. Understanding the origin, current state and reactivity of this carbonaceous material is critical to efforts to detect organic signatures of possible past life on Mars. Environmental effects such as ultraviolet radiation, pressure, diagenesis, aqueous activity, and presence of perchlorates have been assessed previously using analog experiments. To this list, Fox, et al. adds and quantifies the effect of galactic cosmic rays and solar winds on organic material on the surface and in the near subsurface of Mars. Their work, using laboratory analog materials and radiation, shows that the same organic acids, formic and oxalic acid, are produced after exposure equivalent to that over Martian history at depths of less than 5 cm, independent of mineral matrix or starting organic materials. These experiments suggest that planned subsurface exploration using the drill on the Rosalind Franklin Rover (ExoMars) will sample organic material which has not been altered by cosmic rays, although it may have been exposed to other environmental factors such as water or salts.

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Radiolysis of Macromolecular Organic Material in Mars‐Relevant Mineral Matrices

Cited by 36 publications

References 46 publications

The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

Constraints on the Mineralogy and Geochemistry of Vera Rubin Ridge, Gale Crater, Mars, From Mars Science Laboratory Sample Analysis at Mars Evolved Gas Analyses

New Paths for Survivability of Organic Material in the Martian Subsurface

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