Brine-driven destruction of clay minerals in Gale crater, Mars

Development of Martian saline seep models and their implications for planetary protection

While life on Mars has not been found, Earth-based microorganisms may contaminate the Red Planet during rover expeditions and human exploration. Due to the survival advantages conferred by the biofilm morphology to microorganisms, such as resistance to UV and osmotic stress, biofilms are particularly concerning from a planetary protection perspective. Modeling and data from the NASA Phoenix mission indicate that temporary liquid water might exist on Mars in the form of high salinity brines. These brines could provide colonization opportunities for terrestrial microorganisms brought by spacecraft or humans. To begin testing for potential establishment of microbes, results are presented from a simplified laboratory model of a Martian saline seep inoculated with sediment from Hailstone Basin, a terrestrial saline seep in Montana (USA). The seep was modeled as a sand-packed drip flow reactor at room temperature fed media with either 1 M MgSO₄ or 1 M NaCl. Biofilms were established within the first sampling point of each experiment. Endpoint 16S rRNA gene community analysis showed significant selection of halophilic microorganisms by the media. Additionally, we detected 16S rRNA gene sequences highly similar to microorganisms previously detected in two spacecraft assembly cleanrooms. These experimental models provide an important foundation for identifying microbes that could hitch-hike on spacecraft and may be able to colonize Martian saline seeps. Future model optimization will be vital to informing cleanroom sterilization procedures.

Lacustrine sedimentation by powerful storm waves in Gale crater and its implications for a warming episode on Mars

This investigation documents that the Rugged Terrain Unit, the Stimson formation, and the Greenheugh sandstone were deposited in a 1200 m-deep lake that formed after the emergence of Mt. Sharp in Gale crater, Mars, nearly 4 billion years ago. In fact, the Curiosity rover traversed on a surface that once was the bottom of this lake and systematically examined the strata that were deposited in its deepest waters on the crater floor to layers that formed along its shoreline on Mt. Sharp. This provided a rare opportunity to document the evolution of one aqueous episode from its inception to its desiccation and to determine the warming mechanism that caused it. Deep water lacustrine siltstones directly overlie conglomerates that were deposited by mega floods on the crater floor. This indicates that the inception phase of the lake was sudden and took place when flood waters poured into the crater. The lake expanded quickly and its shoreline moved up the slope of Mt. Sharp during the lake-level rise phase and deposited a layer of sandstone with large cross beds under the influence of powerful storm waves. The lake-level highstand phase was dominated by strong bottom currents that transported sediments downhill and deposited one of the most distinctive sedimentological features in Gale crater: a layer of sandstone with a 3 km-long field of meter-high subaqueous antidunes (the Washboard) on Mt. Sharp. Bottom current continued downhill and deposited sandstone and siltstone on the foothills of Mt. Sharp and on the crater floor, respectively. The lake-level fall phase caused major erosion of lacustrine strata that resulted in their patchy distribution on Mt. Sharp. Eroded sediments were then transported to deep waters by gravity flows and were re-deposited as conglomerate and sandstone in subaqueous channels and in debris flow fans. The desiccation phase took place in calm waters of the lake. The aqueous episode we investigated was vigorous but short-lived. Its characteristics as determined by our sedimentological study matches those predicted by an asteroid impact. This suggests that the heat generated by an impact transformed Mars into a warm, wet, and turbulent planet. It resulted in planet-wide torrential rain, giant floods on land, powerful storms in the atmosphere, and strong waves in lakes. The absence of age dates prevents the determination of how long the lake existed. Speculative rates of lake-level change suggest that the lake could have lasted for a period ranging from 16 to 240 Ky.

Observational constraints on the process and products of Martian serpentinization

The alteration of olivine-rich rocks to serpentine minerals, (hydr)oxides, and aqueous hydrogen through serpentinization is long thought to have influenced the distribution of habitable environments on early Mars and the evolution of the early Martian hydrosphere and atmosphere. Nevertheless, the planetary importance of Martian serpentinization has remained a matter of debate. To constrain the process and products of Martian serpentinization, we studied serpentinized iron-rich olivines from the 1.1-billion-year Duluth Complex. These data indicate that serpentinized iron-rich olivine would have been accompanied by a fivefold increase in hydrogen production relative to serpentinized terrestrial mantle peridotites. In contrast to previous expectations, this style of serpentinization yields hisingerite as the dominant iron serpentine mineral at comparatively low temperature and pH, consistent with meteorite mineralogy and in situ rover data. The widespread occurrence of oxidized iron-bearing phyllosilicates in highly magnetized regions of the Martian crust supports the hypothesis that serpentinization was more pervasive on early Mars than currently estimated.

The Curiosity Rover's Exploration of Glen Torridon, Gale Crater, Mars: An Overview of the Campaign and Scientific Results

The Mars Science Laboratory rover, Curiosity, explored the clay mineral-bearing Glen Torridon region for 1 Martian year between January 2019 and January 2021, including a short campaign onto the Greenheugh pediment. The Glen Torridon campaign sought to characterize the geology of the area, seek evidence of habitable environments, and document the onset of a potentially global climatic transition during the Hesperian era. Curiosity roved 5 km in total throughout Glen Torridon, from the Vera Rubin ridge to the northern margin of the Greenheugh pediment. Curiosity acquired samples from 11 drill holes during this campaign and conducted the first Martian thermochemolytic-based organics detection experiment with the Sample Analysis at Mars instrument suite. The lowest elevations within Glen Torridon represent a continuation of lacustrine Murray formation deposits, but overlying widespread cross bedded sandstones indicate an interval of more energetic fluvial environments and prompted the definition of a new stratigraphic formation in the Mount Sharp group called the Carolyn Shoemaker formation. Glen Torridon hosts abundant phyllosilicates yet remains compositionally and mineralogically comparable to the rest of the Mount Sharp group. Glen Torridon samples have a great diversity and abundance of sulfur-bearing organic molecules, which are consistent with the presence of ancient refractory organic matter. The Glen Torridon region experienced heterogeneous diagenesis, with the most striking alteration occurring just below the Siccar Point unconformity at the Greenheugh pediment. Results from the pediment campaign show that the capping sandstone formed within the Stimson Hesperian aeolian sand sea that experienced seasonal variations in wind direction.

From Lake to River: Documenting an Environmental Transition Across the Jura/Knockfarril Hill Members Boundary in the Glen Torridon Region of Gale Crater (Mars)

Between January 2019 and January 2021, the Mars Science Laboratory team explored the Glen Torridon (GT) region in Gale crater (Mars), known for its orbital detection of clay minerals. Mastcam, Mars Hand Lens Imager, and ChemCam data are used in an integrated sedimentological and geochemical study to characterize the Jura member of the upper Murray formation and the Knockfarril Hill member of the overlying Carolyn Shoemaker formation in northern GT. The studied strata show a progressive transition represented by interfingering beds of fine-grained, recessive mudstones of the Jura member and coarser-grained, cross-stratified sandstones attributed to the Knockfarril Hill member. Whereas the former are interpreted as lacustrine deposits, the latter are interpreted as predominantly fluvial deposits. The geochemical composition seen by the ChemCam instrument show K₂O-rich mudstones (∼1-2 wt.%) versus MgO-rich sandstones (>6 wt.%), relative to the average composition of the underlying Murray formation. We document consistent sedimentary and geochemical data sets showing that low-energy mudstones of the Jura member are associated with the K-rich endmember, and that high-energy cross-stratified sandstones of the Knockfarril Hill member are associated with the Mg-rich endmember, regardless of stratigraphic position. The Jura to Knockfarril Hill transition therefore marks a significant paleoenvironmental change, where a long-lived and comparatively quiescent lacustrine setting progressively changes into a more energetic fluvial setting, as a consequence of shoreline regression due to either increased sediment supply or lake-level drop.

Self-Assembled Structures Formed in CO2-Enriched Atmospheres: A Case-Study for Martian Biomimetic Forms

The aim of this study was to investigate the biomimetic precipitation processes that follow the chemical-garden reaction of brines of CaCl₂ and sulfate salts with silicate in alkaline conditions under a Mars-type CO₂-rich atmosphere. We characterize the precipitates with environmental scanning electron microscope micrography, micro-Raman spectroscopy, and X-ray diffractometry. Our analysis results indicate that self-assembled carbonate structures formed with calcium chloride can have vesicular and filamentary features. With magnesium sulfate as a reactant a tentative assignment with Raman spectroscopy indicates the presence of natroxalate in the precipitate. These morphologies and compounds appear through rapid sequestration of atmospheric CO₂ by alkaline solutions of silica and salts.

Orbital and In-Situ Investigation of Periodic Bedrock Ridges in Glen Torridon, Gale Crater, Mars

Gale crater, the field site for NASA's Mars Science Laboratory Curiosity rover, contains a diverse and extensive record of aeolian deposition and erosion. This study focuses on a series of regularly spaced, curvilinear, and sometimes branching bedrock ridges that occur within the Glen Torridon region on the lower northwest flank of Aeolis Mons, the central mound within Gale crater. During Curiosity's exploration of Glen Torridon between sols ∼2300-3080, the rover drove through this field of ridges, providing the opportunity for in situ observation of these features. This study uses orbiter and rover data to characterize ridge morphology, spatial distribution, compositional and material properties, and association with other aeolian features in the area. Based on these observations, we find that the Glen Torridon ridges are consistent with an origin as wind-eroded bedrock ridges, carved during the exhumation of Mount Sharp. Erosional features like the Glen Torridon ridges observed elsewhere on Mars, termed periodic bedrock ridges (PBRs), have been interpreted to form transverse to the dominant wind direction. The size and morphology of the Glen Torridon PBRs are consistent with transverse formative winds, but the orientation of nearby aeolian bedforms and bedrock erosional features raise the possibility of PBR formation by a net northeasterly wind regime. Although several formation models for the Glen Torridon PBRs are still under consideration, and questions persist about the nature of PBR-forming paleowinds, the presence of PBRs at this site provides important constraints on the depositional and erosional history of Gale crater.

Astrobiological Potential of Fe/Mg Smectites with Special Emphasis on Jezero Crater, Mars 2020 Landing Site

Life is known to adapt in accordance with its surrounding environment and sustainable resources available to it. Since harsh conditions would have precluded any possible aerobic evolution of life at the martian surface, it is plausible that martian life, should it exist, would have evolved in such a way as to derive energy from more optimum resources. Iron is one of the most abundant elements present in the martian crust and occurs at about twice the amount present on Earth. Clay minerals contribute to about half the iron found in soils and sediments. On Earth, clay acts as an electron donor as well as an acceptor in the carbon cycles and thereby supports a wide variety of metabolic reactions. In this context, we consider the potential of Fe/Mg smectites, one of the most widely reported hydrated minerals on Mars, for preservation of macro- and microscopic biosignatures. We proceed by understanding the environmental conditions during the formation of smectites and various microbes and metabolic processes associated with them as indicated in Earth-based studies. We also explore the possibility of biosignatures and their identification within the Mars 2020 landing site (Jezero Crater) by using the astrobiological payloads on board the Perseverance rover.

Mission Overview and Scientific Contributions from the Mars Science Laboratory Curiosity Rover After Eight Years of Surface Operations

NASA's Mars Science Laboratory mission, with its Curiosity rover, has been exploring Gale crater (5.4° S, 137.8° E) since 2012 with the goal of assessing the potential of Mars to support life. The mission has compiled compelling evidence that the crater basin accumulated sediment transported by marginal rivers into lakes that likely persisted for millions of years approximately 3.6 Ga ago in the early Hesperian. Geochemical and mineralogical assessments indicate that environmental conditions within this timeframe would have been suitable for sustaining life, if it ever were present. Fluids simultaneously circulated in the subsurface and likely existed through the dry phases of lake bed exposure and aeolian deposition, conceivably creating a continuously habitable subsurface environment that persisted to less than 3 Ga in the early Amazonian. A diversity of organic molecules has been preserved, though degraded, with evidence for more complex precursors. Solid samples show highly variable isotopic abundances of sulfur, chlorine, and carbon. In situ studies of modern wind-driven sediment transport and multiple large and active aeolian deposits have led to advances in understanding bedform development and the initiation of saltation. Investigation of the modern atmosphere and environment has improved constraints on the timing and magnitude of atmospheric loss, revealed the presence of methane and the crater's influence on local meteorology, and provided measurements of high-energy radiation at Mars' surface in preparation for future crewed missions. Rover systems and science instruments remain capable of addressing all key scientific objectives. Emphases on advance planning, flexibility, operations support work, and team culture have allowed the mission team to maintain a high level of productivity in spite of declining rover power and funding.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11214-022-00882-7.

Merging Perspectives on Secondary Minerals on Mars: A Review of Ancient Water-Rock Interactions in Gale Crater Inferred from Orbital and In-Situ Observations

Phyllosilicates, sulfates, and Fe oxides are the most prevalent secondary minerals detected on Mars from orbit and the surface, including in the Mars Science Laboratory Curiosity rover’s field site at Gale crater. These records of aqueous activity have been investigated in detail in Gale crater, where Curiosity’s X-ray diffractometer allows for direct observation and detailed characterization of mineral structure and abundance. This capability provides critical ground truthing to better understand how to interpret Martian mineralogy inferred from orbital datasets. Curiosity is about to leave behind phyllosilicate-rich strata for more sulfate-rich terrains, while the Mars 2020 Perseverance rover is in its early exploration of ancient sedimentary strata in Jezero crater. It is thus an appropriate time to review Gale crater’s mineral distribution from multiple perspectives, utilizing the range of chemical, mineralogical, and spectral measurements provided by orbital and in situ observations. This review compares orbital predictions of composition in Gale crater with higher fidelity (but more spatially restricted) in situ measurements by Curiosity, and we synthesize how this information contributes to our understanding of water-rock interaction in Gale crater. In the context of combining these disparate spatial scales, we also discuss implications for the larger understanding of martian surface evolution and the need for a wide range of data types and scales to properly reconstruct ancient geologic processes using remote methods.

A Review of the Phyllosilicates in Gale Crater as Detected by the CheMin Instrument on the Mars Science Laboratory, Curiosity Rover

Curiosity, the Mars Science Laboratory (MSL) rover, landed on Mars in August 2012 to investigate the ~3.5-billion-year-old (Ga) fluvio-lacustrine sedimentary deposits of Aeolis Mons (informally known as Mount Sharp) and the surrounding plains (Aeolis Palus) in Gale crater. After nearly nine years, Curiosity has traversed over 25 km, and the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on-board Curiosity has analyzed 30 drilled rock and three scooped soil samples to date. The principal strategic goal of the mission is to assess the habitability of Mars in its ancient past. Phyllosilicates are common in ancient Martian terrains dating to ~3.5–4 Ga and were detected from orbit in some of the lower strata of Mount Sharp. Phyllosilicates on Earth are important for harboring and preserving organics. On Mars, phyllosilicates are significant for exploration as they are hypothesized to be a marker for potential habitable environments. CheMin data demonstrate that ancient fluvio-lacustrine rocks in Gale crater contain up to ~35 wt. % phyllosilicates. Phyllosilicates are key indicators of past fluid–rock interactions, and variation in the structure and composition of phyllosilicates in Gale crater suggest changes in past aqueous environments that may have been habitable to microbial life with a variety of possible energy sources.