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

Quantitative High-Resolution Re-Examination of a Hypothesized Ocean Shoreline in Cydonia Mensae on Mars

Dataset in support of research submitted to the Journal of Geophysical Research: Planets

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

GEOMORPHOLOGY AND RELATIVE AGES OF CHANNEL BELT DEPOSITS IN JEZERO'S WESTERN DELTA

International audienceIntroduction: The western delta [1] in Jezero crater is composed of a sequence which includes finely layered planar strata, truncated curvilinear strata, and blocky deposits [2], interpreted as prodelta deposits, laterally accreting point-bars formed in meandering channels, and coarse-grained fluvial channel belt deposits, respectively [3-5]. The Mars 2020 Perseverance rover is completing its investigation of the lowest strata exposed within the western delta scarp [6], and will soon embark on a traverse across the delta “top,” during which it will encounter these curvilinear strata and “blocky” channel belt deposits.Here we use orbiter images and digital terrain models to map and characterize the ridge-forming blocky deposits of the western delta, reconstructing the time-order of channel belt deposition within the upper delta. We also re-examine the stratigraphic relationship between the ridges and the underlying curvilinear and planar layered deposits, as well as the largest impact craters on the top surface of the delta

GEOMORPHOLOGY AND RELATIVE AGES OF CHANNEL BELT DEPOSITS IN JEZERO'S WESTERN DELTA

International audienceIntroduction: The western delta [1] in Jezero crater is composed of a sequence which includes finely layered planar strata, truncated curvilinear strata, and blocky deposits [2], interpreted as prodelta deposits, laterally accreting point-bars formed in meandering channels, and coarse-grained fluvial channel belt deposits, respectively [3-5]. The Mars 2020 Perseverance rover is completing its investigation of the lowest strata exposed within the western delta scarp [6], and will soon embark on a traverse across the delta “top,” during which it will encounter these curvilinear strata and “blocky” channel belt deposits.Here we use orbiter images and digital terrain models to map and characterize the ridge-forming blocky deposits of the western delta, reconstructing the time-order of channel belt deposition within the upper delta. We also re-examine the stratigraphic relationship between the ridges and the underlying curvilinear and planar layered deposits, as well as the largest impact craters on the top surface of the delta

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

Insights into the Sedimentary Record and Processes of the Western Delta of Jezero crater (Mars) as observed by the Mars 2020 rover Perseverance. (Invited)

International audienceSince its landing in Jezero crater in February 2021, the western delta of Jezero has been one of the main targets for the Perseverance rover to explore and sample sedimentary rocks that lead us to better understand the environmental evolution of the region, and could host traces of past biosignatures.During the first year, the rover explored the floor of Jezero crater, focusing on aqueously altered igneous rocks. It also provided the opportunity to remotely observe the main delta front and its remnants (e.g., the Kodiak butte). This allowed us to distinguish several beds of sandstones (with local occurrences of boulders up to 30 cm) arranged into bottomsets, foresets and topsets morphologies. This tripartite geometry and steep slopes of foresets are characteristic of a Gilbert-type delta, formed by the deposition of fluvial sediments prograding into a standing body of water, here a paleolake whose level can be constrained by the transition from the foresets to topsets. Massive beds of boulder conglomerates (with boulders up to 1.5 m) have also been observed at or close to the top of many locations along the delta’s front, hinting at a transition to higher energy flows. Collectively, these elements argue for a polyphase complex depositional history of the delta through time.The toe of the current delta front was reached by the rover on Sol 422 (April 2022) when Perseverance arrived at the Enchanted Lake outcrop, at the base of the southeastern end of the promontory informally named Cape Nukshak on the distal end of the delta. The first in-place sedimentary rocks that were observed were a succession of thinly-laminated medium/coarse sandstones and mudstones. Then, Perseverance pursued its route towards the delta and started its ascension at Hawksbill Gap to assess the first half of the lower delta succession. Strata at the base of Hawksbill Gap are mostly composed of fine to coarse-grained rocks ranging from mudstones to granule conglomerates, displaying planar to low-angle cross-stratifications.These fine-grained detrital rocks are likely to have been deposited by fluvial to deltaic processes. There, the rover collected the first sets of paired sedimentary rock samples (coarse sandstone to micro-conglomerate) that will represent the fine- and coarse-grained lower delta succession once returned to Earth

Insights into the Sedimentary Record and Processes of the Western Delta of Jezero crater (Mars) as observed by the Mars 2020 rover Perseverance. (Invited)

International audienceSince its landing in Jezero crater in February 2021, the western delta of Jezero has been one of the main targets for the Perseverance rover to explore and sample sedimentary rocks that lead us to better understand the environmental evolution of the region, and could host traces of past biosignatures.During the first year, the rover explored the floor of Jezero crater, focusing on aqueously altered igneous rocks. It also provided the opportunity to remotely observe the main delta front and its remnants (e.g., the Kodiak butte). This allowed us to distinguish several beds of sandstones (with local occurrences of boulders up to 30 cm) arranged into bottomsets, foresets and topsets morphologies. This tripartite geometry and steep slopes of foresets are characteristic of a Gilbert-type delta, formed by the deposition of fluvial sediments prograding into a standing body of water, here a paleolake whose level can be constrained by the transition from the foresets to topsets. Massive beds of boulder conglomerates (with boulders up to 1.5 m) have also been observed at or close to the top of many locations along the delta’s front, hinting at a transition to higher energy flows. Collectively, these elements argue for a polyphase complex depositional history of the delta through time.The toe of the current delta front was reached by the rover on Sol 422 (April 2022) when Perseverance arrived at the Enchanted Lake outcrop, at the base of the southeastern end of the promontory informally named Cape Nukshak on the distal end of the delta. The first in-place sedimentary rocks that were observed were a succession of thinly-laminated medium/coarse sandstones and mudstones. Then, Perseverance pursued its route towards the delta and started its ascension at Hawksbill Gap to assess the first half of the lower delta succession. Strata at the base of Hawksbill Gap are mostly composed of fine to coarse-grained rocks ranging from mudstones to granule conglomerates, displaying planar to low-angle cross-stratifications.These fine-grained detrital rocks are likely to have been deposited by fluvial to deltaic processes. There, the rover collected the first sets of paired sedimentary rock samples (coarse sandstone to micro-conglomerate) that will represent the fine- and coarse-grained lower delta succession once returned to Earth