Frances Rivera-Hernández

Abundant geologic evidence suggests that sediment transport by liquid water on Mars took place across a wide range of atmospheric pressures, from at least ∼100 mbar in the Noachian‐Hesperian to ∼7 mbar average of today. Because these low pressures do not occur naturally on Earth, experimental studies in Mars pressure chambers are required to understand and interpret sediment flows and their deposits. Previous experimental studies show that low surface pressures (∼5–13 mbar) affect the transport and deposition of sediments by liquid water. Building on these studies, we conducted experiments to explore how pressure affects the morphology and stratigraphy of warm‐temperature (>293 K) basaltic sediment‐rich flows under varying Mars‐like pressures (7–1,013 mbar), representative of warmer conditions in the Noachian, Hesperian, and Amazonian epochs. At low pressures, over a warm surface, vaporization‐related processes dominate, resulting in deposits with numerous lobes and surface features like vugs, levees, and high surface roughness and slope. Their stratigraphy is characterized by wavy to convoluted bedding that is laterally discontinuous, consistent with burial and entrainment. In contrast, at higher pressures, deposits have sub‐planar bedding, fewer lobes, and surfaces lacking vugs and levees. Our results suggest that sedimentary deposits formed under periods of low atmospheric pressure may be distinguished from deposits formed under the denser and wetter conditions of early Mars and on Earth based on differences in morphology and stratigraphy. Identifying pressure‐dependent differences could help constrain the atmospheric conditions under which sedimentary deposits formed, providing insights into the climatic evolution of Mars.

Process‐based depositional models for perennially ice‐covered lakes (PICLs) are important for interpreting palaeolake deposits and their connection to past climate. PICLs are only stable under specific climate states, and unlike other ice‐free or seasonally ice‐covered lakes, PICL deposits generally have bimodal grain sizes: mud introduced by streams and glaciers and moderately sorted medium to coarse sand deposited as disseminated grains, mounds and ridges from the ice cover. Previous work implies that ice properties influence the mud‐to‐sand ratio and sand depositional style. Here we present multi‐year observations from Lake Joyce, Antarctica, demonstrating how ice cover properties influence deposition to help inform interpretations of climate from the sedimentary record. Lake Joyce's ice cover had smooth to rough textures with rougher ice trapping more sediment and forming multi‐grain sediment pods, and smooth ice containing scattered grains. Low‐albedo medium sand grains preferentially melted into the ice over higher albedo grains and those that are finer and coarser. Thicker pods slowed underlying ice melt, whereas thinner pods accelerated it. Grains migrated downwards and accumulated at an equilibrium depth which was shallower than the ice cover thickness. Sediment pods commonly contained inverse grading, resulting from deflation and preferential melting of finer grains into the ice. These observations help inform PICL deposit interpretations: pods in rough ice result in sand mounds and ridges, while scattered grains on smooth ice lead to disseminated grains. Deposits have a narrow grain‐size range due to the preferential melting of medium sand, and inverse grading in mounds mirrors that of pods. Our observations suggest that ice roughness and thickness control where and how much sediment accumulates, its vertical migration through the ice and depositional style. Temporal or spatial variations in ice properties may be preserved as stratigraphic or lateral facies changes. Because ice properties are climate‐dependent, stratigraphic variations in PICL facies may be used as palaeoclimate indicators if found on Earth and Mars.

Thousands of saline to hypersaline lakes exist across the Yilgarn Craton in Western Australia, representing potential Mars analogs with diverse and varying salinity, pH, and oxygen conditions that remain poorly constrained. Here, we report geochemical trends in lake waters that vary across wet‐dry cycles as well as with regional location and geomorphic setting within the craton's paleovalley system. We identify two different geochemical regimes: (a) lakes where groundwater is more acidic than lake water, and shifts in composition reflect changing precipitation, and (b) lakes that are more acidic than local groundwater due to subsurface and surface geochemical interactions. Elevated salinity in all lakes relative to groundwater occurs due to cyclic evaporation driven by strong seasonal forcing. Most lakes occupy shallow, surficial basins that lack exposed outcrops. Lakes that are deeply incised expose truncated lateritic profiles dominated by clay minerals, quartz veins, and Fe‐oxides. These contrasting settings represent geologic and geochemical endmembers across the region, for which interactions between evaporative concentration and acidic groundwater shape the geochemical evolution of lake systems differently. These factors, in turn, influence microbial habitability, the deposition of salts and other surficial indicators of environmental change. Our observations reveal visible signatures of prolonged acidic‐groundwater interactions, including features consistent with Fe redox cycling, and recurring wet‐dry cycles. These findings suggest that paleodrainage systems within and near craters in Mars' Terra Sirenum, which host similar layered and bleached Al‐rich clay outcrops with smaller exposures of acidic weathered minerals, may record evaporitic concentration and potentially long‐duration groundwater interactions.

Serpentinization produces hydrogen and methane through abiotic water‐rock interactions, potentially supporting chemotrophic life in planetary subsurface environments. Serpentine deposits in the Martian Noachian landscapes of Nili Fossae and the Southern Highlands have been considered as potential paleo‐habitable zones. However, the geochemical and physical conditions of Martian serpentinization fluids are poorly constrained because of limited data on serpentinite composition and formation environment. Furthermore, the co‐occurrence of magnesite and magnesium‐enriched serpentines on Mars remains enigmatic. To address such gaps, we investigated antigorite‐magnesite paleo‐serpentine bodies along the Highland‐Vijayan suture of Sri Lanka as Martian analog sites, using thermodynamic batch reaction models to constrain alteration fluids and the production of primary (H ₂ ) and secondary (CH ₄ ) serpentinization products. Geochemist's Workbench models combined field X‐Ray Fluorescence (XRF) observations with varied protolith compositions (ultramafic or gneissic), precursor fluids (seawater or freshwater), temperatures (100–600°C), volumetric water‐to‐rock ratios (1–100,000), and CO ₂ partial pressures (0.01–1 bar). Models successfully reproduced the co‐occurrence of antigorite and magnesite observed on Mars, with both minerals forming at 100°C across water‐to‐rock ratios. Despite their Mg‐enriched composition, ultramafic protoliths produced H ₂ yields (up to 229 mmol/kg at W/R 1 at 100°C), supporting chemotrophic populations up to 10 ^7.5 cells/mL. Geochemical models indicate Mg enrichment from ultramafic mineralogy and Fe contribution from regional gneisses. Our thermodynamic equilibrium results show that Mg‐rich serpentine systems with sufficient ferrous iron can produce biologically significant H ₂ , establishing Sri Lankan serpentinites as valuable analogs for Noachian Mars habitability.

Bonestell Crater in Acidalia Planitia and a ∼13 km‐diameter crater to the northwest preserve geomorphic and thermophysical evidence of Amazonian‐aged glacial activity. In Bonestell, lobate deposits along the northwestern rim and a cirque‐like depression along the southeastern rim display steep scarps, lineated textures, and polygonal surface patterns consistent with debris‐covered ice and periglacial modification. The cirque depression contains thrust‐like ridges and compressional structures resembling terrestrial glacial cirques, interpreted as a remnant of polythermal glaciation, where cold‐ and warm‐based ice likely coexisted. Thermal inertia values across these deposits range from ∼300 to 800 J·M ⁻² K ⁻¹ ·s ^−1/2 , suggesting a downslope transition from poorly consolidated sediment to indurated material. CRISM spectra reveal hydrated minerals and altered silicates consistent with episodic basal melting or volatile‐driven alteration. In contrast, the unnamed northwest crater hosts clear examples of rock glaciers. Multiple lobate flows descend from alcoves along the crater walls, exhibiting convex‐upward profiles, degraded termini, and compressive ridges that closely resemble terrestrial debris‐covered glaciers. HiRISE image data show flow‐parallel lineations and banding indicative of internal deformation and sublimation‐driven modification. Spectral unmixing of THEMIS ROTO data acquired from multiple viewing geometries fit modeled mixtures of sand and indurated crust with thermal inertia values ∼600 J·M ⁻² K ⁻¹ ·s ^−1/2 , consistent with debris‐coated ice. These results demonstrate that mid‐latitude ice in the region is preserved in diverse forms, including cirques, rock glaciers, and debris‐mantled ice masses. Their co‐occurrence indicates that Amazonian glaciation was not singular nor isolated but regionally extensive and capable of producing transient wet‐based conditions that locally sustained liquid water and habitable environments.

Saline lakes are expected to have been extensively present on ancient Mars, particularly as the planet dried or cooled. Such lakes likely deposited sulfate salts, as these salts have been widely identified from orbital and in situ Mars data. However, the relationship between martian sulfates and the environmental conditions that formed them (including whether conditions were warm, cool, drying, or freezing), remains under‐characterized. To evaluate the relationship between sulfates and climate, we investigated the hypersaline, sulfate‐bearing Basque Lakes in British Columbia, Canada, which serve as an analog for both “cold and wet” and “warm and wet” early Mars. We use the rover and orbiter relevant instrument techniques of Raman, Near Infrared, and X‐Ray Fluorescence spectroscopy to evaluate seasonal lake mineralogy. We find that temperature‐dependent, multi‐cation salts form widely within the Basque Lakes' efflorescent crusts in the fall, which transform to meridianiite, mirabilite, a metastable Na‐sulfate 7‐hydrate, and epsomite in the wintertime. In both seasons, salt assemblages are metastable and persist beyond expected thermodynamic stability fields, suggesting ongoing climatic changes can prevent saline systems from settling into equilibrium phases. Coupled with sedimentological evidence, intimately mixed Mg‐sulfates of different hydration states could be an indicator of surface fluids that interacted with an atmosphere, while formation of Na‐sulfates could be evidence for brine freezing. Curiosity's exploration of the Gale crater sulfate‐bearing unit and Perseverance's exploration of Jezero crater on Mars offer excellent chances to investigate the influence of climate on Mg‐sulfate formation.

Landforms created by flowing water with sediment have left deposits on the surface of Mars, allowing study of the ancient environment. These features could provide constraints on surface water activity and past habitability. However, only a few lab studies have investigated the appearance and behavior of sediment-rich flows at relevant Mars surface conditions. We conducted experiments in a Mars environment chamber to understand the rheology and deposit morphology of mud under atmospheric pressures from 5 to 1000 mbar and surface temperatures between 248 and 297 K. We found that sediment flows in the Noachian era, when most aqueous activity occurred, could behave similarly to Earth analogs, but only under certain climate conditions. However, in the Hesperian and Amazonian periods, the dominant physical regime changed due to global atmospheric loss. Sediment flows during these eras would not have been similar to Earth analogs, and would have been dominated by freezing, evaporative cooling, and boiling depending on the microclimate (local pressure and temperature). Thus, regional climate and compositional context are important factors for interpreting satellite remote sensing images of these features on Mars. The results suggest we may be able to discover the paleo-atmospheric pressure record on Mars by analyzing sediment flow morphology.

This study uses data from the Mars Science Laboratory Curiosity rover to document the facies of the Sutton Island member of the Murray formation, interpret paleoenvironments, and establish key stratigraphic transitions at Gale crater. Two facies associations were identified: Facies Association 1 (FA1) and Facies Association 2 (FA2). Individual facies in FA1 include planar‐laminated mudstone with minor intervals of planar sandstone, ripple cross‐laminated sandstone, cross‐stratified sandstone, and alternating laminated sandstone and mudstone. Meter‐thick packages of planar‐laminated mudstone in FA1 are interpreted to represent deposition in low‐energy ponded environments along the lake margin. Straight‐ and curve‐crested ripple cross‐laminated facies are interpreted to represent current‐influenced deposition. Cross‐stratified sandstone facies consist of dm‐thick sets that represent deposition in distal channels. Intercalated mm‐scale mudstone and sandstone laminae represent waning flow conditions and possible channel abandonment. Facies in FA1 collectively represent deposition in a distal delta plain. FA2 is comprised of planar‐laminated mudstone with minor sandstone and is interpreted to represent deposition in a lacustrine‐basin setting by suspension settling linked to density flows. FA1 transitions upward into FA2, defining a rapid transgression substantial enough to facilitate the deposition of distal lake facies above delta plain facies. The abrupt transition from FA2 back to FA1 deltaic deposits is suggestive of forced regression. Facies in FA1 and FA2 are consistent with the prevalence of aqueous environments recorded in other Murray formation members and extend our understanding of the dynamic sedimentary processes that characterized ancient lacustrine systems at Gale crater.

Aeolian processes have shaped and contributed to the geological record in Gale crater, Mars, long after the fluviolacustrine system existed ∼3 Ga ago. Understanding these aeolian deposits, particularly those which have been lithified and show evidence for aqueous alteration, can help to constrain the environment at their time of deposition and the role of liquid water later in Mars' history. The NASA Curiosity rover investigated a prominent outcrop of aeolian sandstone within the Stimson formation at the Greenheugh pediment as part of its investigation of the Glen Torridon area. In this study, we use geochemical data from ChemCam to constrain the effects of aeolian sedimentary processes, sediment provenance, and diagenesis of the sandstone at the Greenheugh pediment, comparing the Greenheugh data to the results from previous Stimson localities situated 2.5 km north and >200 m lower in elevation. Our results, supported by mineralogical data from CheMin, show that the Stimson formation at the Greenheugh pediment was predominately sourced from an olivine‐rich unit that may be present farther up the slopes of Gale crater's central mound. Our results also suggest that the Greenheugh pediment Stimson formation was cemented by surface water runoff such as that which may have formed Gediz Vallis. The lack of alteration features in the Stimson formation at the Greenheugh pediment relative to those of the Emerson and Naukluft plateaus suggests that groundwater was not as available at this locality compared to the others. However, all sites share diagenesis at the unconformity.