Martian Hydrated Minerals: A Significant Water Sink

Abstract

Quantifying the water in all Martian water reservoirs is important for understanding the history of water on Mars, including Mars' past climate and potential for habitability. Hydrated minerals are widespread on Mars and may comprise a significant portion of the water inventory. We calculated the possible volumes of water stored within and required to form hydrated minerals on Mars by estimating the weight percent (wt.%) water of ice free, near surface materials, the wt.% water required to form subsurface hydrated minerals, and the densities and thicknesses of rock units with hydrated minerals. We estimated the near surface wt.% water using Mars Odyssey Neutron Spectrometer and OMEGA 3 µm hydration feature surveys. We calculated the wt.% water required to form subsurface hydrated minerals by estimating: (1) percent occurrences of subsurface hydrated minerals using mineralogical crater surveys, (2) abundance per detection of hydrated minerals using published spectral unmixing results of hydrated mineral detections, and (3) the wt.% water required to form hydrated minerals using estimated masses and hydration states of hydrated minerals. We estimated the densities of rock units with hydrated minerals using prior crustal density estimates and measurements of sedimentary rock density in Gale Crater. We estimated the thicknesses of rock units with hydrated minerals using mineralogical crater surveys. Our best estimate for the volume of water stored within or required to form hydrated minerals on Mars is 130-260 m global equivalent layer (GEL) and our plausible range extends from 70-860 m GEL. Compared to other Martian reservoirs, hydrated minerals are a significant water sink.