Remote Detection of Phyllosilicates on Mars and Implications for Climate and Habitability

Abstract Identification of phyllosilicates and short-range ordered (SRO) materials on Mars has led to new insights about the early martian climate and habitability. Phyllosilicates were first conclusively identified on Mars in 2005 using visible/near-infrared (VNIR) remote sensing by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activite (OMEGA) instrument. Following these detections, phyllosilicates and poorly crystalline aluminosilicates were documented in numerous large and small outcrops using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) VNIR instrument. Analyses of the Thermal Emission Spectrometer (TES) imagery also support the presence of phyllosilicates and SRO materials in several locations on Mars. These orbital detections are reinforced by measurements taken by the Chemistry and Mineralogy (CheMin) instrument on the Mars Science Laboratory (MSL) rover at Gale Crater. Characterization of Mars analog materials containing phyllosilicates such as smectites, kaolin-serpentine group clay minerals, chlorites, mica, talc, prehnite, and SRO phases such as hydrated silica, allophane, imogolite, ferrihydrite, schwertmannite, and akaganeite has enabled constraints to be placed on the geochemical conditions of formation for alteration materials on Mars. Association of phyllosilicates with related minerals such as carbonates, sulfates, iron oxides/hydroxides, and Cl salts on Mars provides further constraints on the temperature, pH, salinity, and water/rock ratio of potentially habitable environments on Mars. These observations together support warm and wet conditions on early Mars where liquid water was stable on the surface during parts of the Noachian, followed by periods during the Hesperian and Amazonian where surface water was only transient. Subsurface alteration and formation of clays also occurred on Mars during its early history and may have enabled the formation of clay minerals more recently when surface conditions no longer could support liquid water. Both surface and subsurface aqueous environments could have provided important niches for astrobiology on Mars. The phyllosilicates and associated minerals formed in subaqueous and subaerial surface environments on Mars provide constraints on the climate. Smectite clays that formed in surface environments mark a time when liquid water was stable on the surface with temperatures likely 20°C or warmer. Transitions to SRO materials rather than phyllosilicates on Mars indicate a change in climate to colder conditions where water was only transiently present on the surface.