Anoxic atmospheres on Mars driven by volcanism : implications for past environments and life

This work was supported by NNX10AN67G grant from NASA's Mars Fundamental Research Program awarded to DCC.Mars today has no active volcanism and its atmosphere is oxidizing, dominated by the photochemistry of CO2 and H2O. Mars experienced widespread volcanism in the past and volcanic emissions should have included reducing gases, such as H2 and CO, as well as sulfur-bearing gases. Using a one-dimensional photochemical model, we consider whether plausible volcanic gas fluxes could have switched the redox-state of the past martian atmosphere to reducing conditions. In our model, the total quantity and proportions of volcanic gases depend on the water content, outgassing pressure, and oxygen fugacity of the source melt. We find that, with reasonable melt parameters, the past martian atmosphere (∼3.5 Gyr to present) could have easily reached reducing and anoxic conditions with modest levels of volcanism, >0.14 km3 yr−1, which are well within the range of estimates from thermal evolution models or photogeological studies. Counter-intuitively we also find that more reducing melts with lower oxygen fugacity require greater amounts of volcanism to switch a paleo-atmosphere from oxidizing to reducing. The reason is that sulfur is more stable in such melts and lower absolute fluxes of sulfur-bearing gases more than compensate for increases in the proportions of H2 and CO. These results imply that ancient Mars should have experienced periods with anoxic and reducing atmospheres even through the mid-Amazonian whenever volcanic outgassing was sustained at sufficient levels. Reducing anoxic conditions are potentially conducive to the synthesis of prebiotic organic compounds, such as amino acids, and are therefore relevant to the possibility of life on Mars. Also, anoxic reducing conditions should have influenced the type of minerals that were formed on the surface or deposited from the atmosphere. We suggest looking for elemental polysulfur (S8) as a signature of past reducing atmospheres. Finally, our models allow us to estimate the amount of volcanically sourced atmospheric sulfate deposited over Mars’ history, approximately ∼106-109 Tmol, with a spread depending on assumed outgassing rate history and magmatic source conditions.PostprintPeer reviewe

Geomorphic and Atmospheric Investigations on the Habitability of Past and Present Mars

Thesis (Ph.D.)--University of Washington, 2019While the current surface of Mars is viewed to be inhospitable to life as we know it, past Mars may have harbored habitable environments though the extent and duration of such environment is still unclear. There are several requirements to make an environment habitable, which include a liquid solvent (e.g. liquid water), a source of energy (e.g. redox gradients), bioimportant major and trace elements (e.g. CHNOPS), and sustained clement conditions for necessary biochemical reactions to take place (e.g. temperature, pH). This dissertation focuses on better constraining these requirements through atmospheric modeling and quantitative surficial geomorphological investigations. The first half of this dissertation explores the habitability of past and present Mars through the lens of atmospheric redox chemistry. The photochemically produced CO-O2 redox pair in the modern atmosphere produces the second largest atmospheric thermodynamic disequilibrium in the solar system (behind Earth’s atmosphere-ocean system), which represents an untapped source of free energy for potential life to exploit. A rigorous upper limit on the possible extant biomass that can be sustained from this free energy is presented. Volcanic outgassing of reducing gases, e.g. CO and H2, can shift the redox state of the atmosphere, changing the surface conditions towards being reducing and anoxic which are more favorable for the formation of prebiotic chemical compounds (e.g. amino acids). The required levels of volcanism needed to create reducing conditions and potential observables of such environments are also presented here. The latter half of this dissertation focuses on assessing the current state of coastal evidence for past liquid water oceans on Mars. While nearly all aspects of these hypothesized oceans are vigorously debated, availability of large sustained bodies of liquid water would be a boon for constraining the past surface habitability. Presented here is a toolkit developed for quantitatively identifying paleoshorelines using topographic, morphological, and spectroscopic investigations. This toolkit is then applied to 40 individual sites across Mars that have been proposed as ancient ocean shorelines and evaluated along with the general mapped contacts on their consistency with such an origin. None of the putative paleoshoreline sites provided compelling evidence nor consistency with a coastal origin and can all be explained through more conservative geological processes. Together, the chapters in this dissertation provide quantitative means of characterizing contributing aspects of potentially habitable environments on past and present Mars

Anoxic atmospheres on Mars driven by volcanism:implications for past environments and life

Mars today has no active volcanism and its atmosphere is oxidizing, dominated by the photochemistry of CO2 and H2O. Mars experienced widespread volcanism in the past and volcanic emissions should have included reducing gases, such as H2 and CO, as well as sulfur-bearing gases. Using a one-dimensional photochemical model, we consider whether plausible volcanic gas fluxes could have switched the redox-state of the past martian atmosphere to reducing conditions. In our model, the total quantity and proportions of volcanic gases depend on the water content, outgassing pressure, and oxygen fugacity of the source melt. We find that, with reasonable melt parameters, the past martian atmosphere (∼3.5 Gyr to present) could have easily reached reducing and anoxic conditions with modest levels of volcanism, >0.14 km3 yr−1, which are well within the range of estimates from thermal evolution models or photogeological studies. Counter-intuitively we also find that more reducing melts with lower oxygen fugacity require greater amounts of volcanism to switch a paleo-atmosphere from oxidizing to reducing. The reason is that sulfur is more stable in such melts and lower absolute fluxes of sulfur-bearing gases more than compensate for increases in the proportions of H2 and CO. These results imply that ancient Mars should have experienced periods with anoxic and reducing atmospheres even through the mid-Amazonian whenever volcanic outgassing was sustained at sufficient levels. Reducing anoxic conditions are potentially conducive to the synthesis of prebiotic organic compounds, such as amino acids, and are therefore relevant to the possibility of life on Mars. Also, anoxic reducing conditions should have influenced the type of minerals that were formed on the surface or deposited from the atmosphere. We suggest looking for elemental polysulfur (S8) as a signature of past reducing atmospheres. Finally, our models allow us to estimate the amount of volcanically sourced atmospheric sulfate deposited over Mars’ history, approximately ∼106-109 Tmol, with a spread depending on assumed outgassing rate history and magmatic source conditions

Mars Helicopter, Ingenuity: Third Year Extended Mission Operations and Results

International audienceThe Mars Helicopter, Ingenuity, is completing its third year operating on Mars. It is a technology demonstration carried on the 2020 Rover to show that flight in the thin Mars atmosphere is possible [1]. The first 18 flights of the mission were summarized in [2]. Surface operations and results from flights 19 through 38 of the 1st extended mission during calendar year 2022 are described in [3]. This abstract describes the third year of surface operations and contributions it has made

Mars Helicopter, Ingenuity: Third Year Extended Mission Operations and Results

International audienceThe Mars Helicopter, Ingenuity, is completing its third year operating on Mars. It is a technology demonstration carried on the 2020 Rover to show that flight in the thin Mars atmosphere is possible [1]. The first 18 flights of the mission were summarized in [2]. Surface operations and results from flights 19 through 38 of the 1st extended mission during calendar year 2022 are described in [3]. This abstract describes the third year of surface operations and contributions it has made

Landscape evolution on early Mars: insights from the Jezero western fan

International audienceThe modern surface of Mars does not sustain liquid water, however relict landforms observed onorbital images provide strong evidence of past aqueous activity. Nevertheless on-the-groundanalysis of sedimentary strata are required to robustly characterise the specific nature of early Marspalaeoenvironments. The Mars 2020 Perseverance rover is exploring a prominent sedimentary fandeposit at the western margin of Jezero crater – the Western fan – which has been interpreted to bean river delta that prograded into an ancient lake basin during the Late Noachian-Early Hesperianepochs on Mars (~3.6-3.8 Ga). Perseverance’s traverse across the fan in 2022-2023 provides aremarkable window into a fossilised sediment routing system on Mars with potential to understandhow water and sediment were distributed across a Martian landscape under a markedly differentclimate to present day. Here we use the rover’s cameras to characterise sedimentary geometries ina distal to proximal transect across the western fan and reconstruct sediment dynamics on theWestern fan and infer past environmental change. The distal reaches of the preserved fan show asedimentary succession that records a transition from distal alluvial fan into lacustrine andsubsequently foreset delta deposits. This succession records the initiation of a martian lake systemand lake level rise, though overlying delta stratal geometries suggest deposition during episodes oflake level fall. In the medial sector of the upper exhumed portion of the fan, complex stratalgeometries are observed with a variety of scenarios for palaeoenvironmental interactions possible.In particular, the presence of large-scale foreset units preserved in this ‘mid-fan’ sector possiblysuggests complex deltaic interfingering with fluvial strata during lake level fluctuations. In moreproximal and stratigraphically higher (and hence younger) sectors of the fan, we observe stratadeposited by progradation of fluvial systems culminating in a sequence of rounded bouldercontainingdeposits that signal transition to a routing system characterised by high discharges.Misquoting Shakira “the sediments don’t lie”; they record a history of sustained water transport andhabitability on early Mars

DIGITAL THREE-DIMENSIONAL MAPPING OF THE STRATIGRAPHIC ARCHITECTURE OF THE JEZERO WESTERN FAN FRONT

International audienceThe NASA Mars2020 rover Perseverance traversed series that represent the transition from crater floor lithologies to deposits of the Jezero western fan during its second Earth year of rover operations. During that time, the mission explored the exposed stratigraphic succession at the delta front, named the Shenandoah formation. The main science camera on the rover, Mastcam-Z, collects stereo-images of outcrops encountered in visible to near infrared wavelengths at focal lengths ranging from 34 to 110 mm. We use the Planetary Robotics Vision Processing and Planetary Robotics 3-D Viewer tools (PRoViP and PRo3D respectively) for processing, viewing and analysing correctly scaled and located 3-D digital outcrop models using Mastcam-Z stereo-images. Scaling and georeferencing of the models is achieved by incorporation of detailed camera models, image metadata detailing the camera pointing azimuths, focus, exposure and rover attititude, and spatial metadata obtained through incorporation and conversion of SPICE kernels. We can visualise these digital outcrop datasets overlain on high resolution orbital terrain data to measure the geometry of geological bodies and correlate observations between rover positions.Four cross-sections were constructed across the lower delta stratigraphy at the base of Hawksbill Gap and Cape Nukshak using data collected from 3D reconstructions of Mastcam-Z stereo-images and HiRISE topography. Lithological observations made from Mastcam-Z image mosaics were used to inform interpretations on multiple 3D reconstructions of stereo-image data. Stratigraphic boundaries based on team analyses, and the key dip and dip azimuth measurements, were mapped in PRo3D and plotted on topographic profiles to visualise the depositional architecture. Stratigraphic thicknesses were corrected for dip, where necessary, to build stratigraphic logs. The basal surfaces of the identified members which comprise the Shenandoah formation were correlated between the lines of section to illustrate the architectural variations across the delta front. We show that the overall boundaries of the stratigraphic units identified are sub-horizontal at the 100s of metre scale but show considerable variation in some locations at the sub-metre scale, largely as a result of soft sediment deformation, and the limited development of scours and low angle cross-stratification

CONSTRUCTING GEOLOGICAL CROSS-SECTIONS TO CONSTRAIN THE THREE-DIMENSIONAL STRATIGRAPHIC ARCHITECTURE OF THE JEZERO DELTA FRONT

International audienceThe NASA Mars2020 rover Perseverance has been traversing series that represent the transition from crater floor lithologies to deposits of the Jezero western delta since Sol 422 of rover operations [1]. During that time, the mission has explored the exposed stratigraphic succession at the delta front, named the Shenandoah formation [2]. Here we analyse Mastcam-Z mosaics and 3D data products derived from Planetary Robotics processing and viewing tools (PRoViP and PRo3D [3]) to map the 3D geometry of key stratigraphic boundaries and document the 3D stratigraphic architecture at the sub-km- to m-scale within the Shenandoah formation

CONSTRUCTING GEOLOGICAL CROSS-SECTIONS TO CONSTRAIN THE THREE-DIMENSIONAL STRATIGRAPHIC ARCHITECTURE OF THE JEZERO DELTA FRONT

International audienceThe NASA Mars2020 rover Perseverance has been traversing series that represent the transition from crater floor lithologies to deposits of the Jezero western delta since Sol 422 of rover operations [1]. During that time, the mission has explored the exposed stratigraphic succession at the delta front, named the Shenandoah formation [2]. Here we analyse Mastcam-Z mosaics and 3D data products derived from Planetary Robotics processing and viewing tools (PRoViP and PRo3D [3]) to map the 3D geometry of key stratigraphic boundaries and document the 3D stratigraphic architecture at the sub-km- to m-scale within the Shenandoah formation

The Complex Exhumation History of Jezero Crater Floor Unit and Its Implication for Mars Sample Return

During the first year of NASA's Mars 2020 mission, Perseverance rover has investigated the dark crater floor unit of Jezero crater and four samples of this unit have been collected. The focus of this paper is to assess the potential of these samples to calibrate the crater-based Martian chronology. We first review the previous estimation of crater-based model age of this unit. Then, we investigate the impact crater density distribution across the floor unit. It reveals that the crater density is heterogeneous from areas which have been exposed to the bombardment during the last 3 Ga to areas very recently exposed to bombardment. It suggests a complex history of exposure to impact cratering. We also display evidence of several remnants of deposits on the top of the dark floor unit across Jezero below which the dark floor unit may have been buried. We propose the following scenario of burying/exhumation: the dark floor unit would have been initially buried below a unit that was a few tens of meters thick. This unit then gradually eroded away due to Aeolian processes from the northeast to the west, resulting in uneven exposure to impact bombardment over 3 Ga. A cratering model reproducing this scenario confirms the feasibility of this hypothesis. Due to the complexity of its exposure history, the Jezero dark crater floor unit will require additional detailed analysis to understand how the Mars 2020 mission samples of the crater floor can be used to inform the Martian cratering chronology