Detection of Carbonates in Martian Weathering Profiles

Noachian surfaces on Mars exhibit vertical assemblages of weathering horizons termed as weathering profiles; this indicates that surface water caused alteration of the rocks that required a different, warmer climate than today. Evidence of this early Martian climate with CO2 vapor as the main component causing greenhouse warming has been challenged by the lack of carbonate in these profiles. Here we report the analysis of Compact Reconnaissance Imaging Spectrometer for Mars L-detector data leading to the detections of carbonates using a spectral signature exclusively attributed to them. The carbonates are collocated with hydroxylated minerals in weathering profiles over the Martian surface. The origin of CO2 for the formation of carbonates could be the atmosphere. The widespread distribution of weathering profiles with carbonates over the surface of the planet suggest global interactions between fluids containing carbonate/bicarbonate ions with the surface of Mars in the presence of atmospheric water until around 3.7 billion years ago. Plain Language Summary The oldest surface of Mars witnessed an impact of dense and humid atmosphere leading to the formation of hydrated minerals. The analysis of remote sensing data allows identifying carbonates mixed with the hydrated minerals. These associations of carbonates and hydrated minerals are widespread on the surface of the planet. This indicates a planetary-scale process of formation involving the presence of fluids containing inorganic carbon. This finding allows a better understanding of the environment of Mars during the period suspected to be the most likely to have host habitable environment on the planet.