Volumetric estimates of ancient water on Mount Sharp based on boxwork deposits, Gale Crater, Mars

While the presence of water on the surface of early Mars is now well known, the volume, distribution, duration, and timing of the liquid water have proven difficult to determine. This study makes use of a distinctive boxwork-rich sedimentary layer on Mount Sharp to map fluid-based cementation from orbital imagery and estimate the minimum volume of water present when this sedimentary interval was formed. The boxwork structures on Mount Sharp are decameter-scale light-toned polygonal ridges that are unique compared to previous observations of Martian fractured terrain because they are parallel-sided ridges with dark central linear depressions. This texture and the sedimentary setting strongly imply that the ridges are early diagenetic features formed in the subsurface phreatic groundwater zone. High-resolution orbital imagery was used to map the volume of light-toned cemented ridges. Based on the cemented volume, a minimum of 5.25 × 105 m^3 of cement was deposited within the fractures. Using a brine composition based on observations of other Martian cements and modeling the degree of evaporation, each volume of cement requires 800–6700 pore volumes of water, so the mapped boxwork ridge cements require a minimum of 0.43 km^3 of water. This is a significant amount of groundwater that must have been present at the −3620 m level, 1050 m above the current floor of Gale Crater, providing both a new constraint on the possible origins of Mount Sharp and a possible future science target for the Curiosity rover where large volumes of water were present, and early mineralization could have preserved a once-habitable environment

Extraformational sediment recycling on Mars

Extraformational sediment recycling (old sedimentary rock to new sedimentary rock) is a fundamental aspect of Earth's geological record; tectonism exposes sedimentary rock, whereupon it is weathered and eroded to form new sediment that later becomes lithified. On Mars, tectonism has been minor, but two decades of orbiter instrument-based studies show that some sedimentary rocks previously buried to depths of kilometers have been exposed, by erosion, at the surface. Four locations in Gale crater, explored using the National Aeronautics and Space Administration's Curiosity rover, exhibit sedimentary lithoclasts in sedimentary rock: At Marias Pass, they are mudstone fragments in sandstone derived from strata below an erosional unconformity; at Bimbe, they are pebble-sized sandstone and, possibly, laminated, intraclast-bearing, chemical (calcium sulfate) sediment fragments in conglomerates; at Cooperstown, they are pebble-sized fragments of sandstone within coarse sandstone; at Dingo Gap, they are cobble-sized, stratified sandstone fragments in conglomerate derived from an immediately underlying sandstone. Mars orbiter images show lithified sediment fans at the termini of canyons that incise sedimentary rock in Gale crater; these, too, consist of recycled, extraformational sediment. The recycled sediments in Gale crater are compositionally immature, indicating the dominance of physical weathering processes during the second known cycle. The observations at Marias Pass indicate that sediment eroded and removed from craters such as Gale crater during the Martian Hesperian Period could have been recycled to form new rock elsewhere. Our results permit prediction that lithified deltaic sediments at the Perseverance (landing in 2021) and Rosalind Franklin (landing in 2023) rover field sites could contain extraformational recycled sediment.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737

Discovery of Carbonate-Rich Outcrops in the Gusev Crater Columbia Hills by the MER Rover Spirit

The chemical composition, global abundance, distribution, and formation pathways of carbonates are central to understanding aqueous processes, climate, and habitability of early Mars. The Mars Exploration Rover (MER) Spirit analyzed a series of olivine-rich outcrops while descending from the summit region of Husband Hill into the Inner Basin of the Columbia Hills of Gusev Crater to the eastern edge of the El Dorado ripple field in late 2005. Reanalysis of Spirit s mineralogical data from the Moessbauer Spectrometer (MB) and the Miniature Thermal Emission Spectrometer (Mini-TES) and chemical data from the Alpha Particle X-Ray Spectrometer (APXS) in 2010, coupled with new laboratory data for carbonate-bearing samples, lead to identification of carbonate in one of the outcrops (Comanche) [Morris, R.V., et al., Science, 329, 421-424]. The carbonate is rich in magnesium and iron (Mc62Sd25Cc11Rh2, assuming all Ca and Mn is associated with the carbonate) and is a major component of the Comanche outcrops (16 to 34 wt.%). The mineralogical, chemical, and abundance data are constrained in multiple, mutually consistent ways by the MER analyses. For example, a low-Ca carbonate is required by the MB and APXS data and is consistent with Mini-TES data. Three spectral features attributable to fundamental infrared vibrational modes of low-Ca carbonate are present in the Mini-TES spectra of Comanche outcrops. The average composition of Comanche carbonate approximates the average composition of the carbonate globules in Martian meteorite ALH 84001. Analogy with ALH 84001, terrestrial, and synthetic carbonate globules suggests that Comanche carbonate precipitated from aqueous solutions under hydrothermal conditions at near neutral pH in association with volcanic activity during the Noachian era. Comanche outcrop morphology suggests they are remnants of a larger carbonate-bearing formation that evolved in ultramafic rock and then preferentially eroded by a combination of aeolian abrasion and chemical decomposition by exposure to acid-sulfate vapors/solutions. The high carbonate concentration in the Comanche outcrops supports climate models involving a CO2 greenhouse gas on a wet and warm early Mars and subsequent sequestering of at least part of that atmosphere in carbonate minerals

Low Hesperian P_(CO2) constrained from in situ mineralogical analysis at Gale Crater, Mars

Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planetwide evidence of liquid water in the Noachian and Early Hesperian. In this study, we use mineral and contextual sedimentary environmental data measured by the Mars Science Laboratory (MSL) Rover Curiosity to estimate the atmospheric partial pressure of CO_2 (P_(CO2)) coinciding with a long-lived lake system in Gale Crater at ∼3.5 Ga. A reaction–transport model that simulates mineralogy observed within the Sheepbed member at Yellowknife Bay (YKB), by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicates atmospheric P_(CO2) levels in the 10s mbar range. At such low P_(CO2) levels, existing 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 lake waters from being lost to the atmosphere. Thus, either 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 locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO_2 in inferred warmer conditions and valley network formation of the late Noachian

Regional Paleoenvironments Recorded in Sedimentary Rocks of the Western Fan-Delta, Jezero Crater, Mars

International audienceThe Mars 2020 Perseverance rover science team recently completed an investigation of the fan-delta sedimentary sequence [1] and has begun exploration of the crater margin. High resolution chemical, mineralogical, and morphological observations collected with the rover instrument payload provide powerful constraints on rock origins, contextualizing the suite of high-value samples collected as part of the Mars Sample Return campaign

Regional Paleoenvironments Recorded in Sedimentary Rocks of the Western Fan-Delta, Jezero Crater, Mars

International audienceThe Mars 2020 Perseverance rover science team recently completed an investigation of the fan-delta sedimentary sequence [1] and has begun exploration of the crater margin. High resolution chemical, mineralogical, and morphological observations collected with the rover instrument payload provide powerful constraints on rock origins, contextualizing the suite of high-value samples collected as part of the Mars Sample Return campaign

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