Hydrated Silica in Oxia Planum, Mars

Abstract

Hydrated silica (SiO₂·nH₂O; opal) is important for understanding the geological and aqueous history and habitability of Mars, owing to its genesis in a wide range of aqueous environments and its high biosignature preservation potential relative to other hydrated minerals. Utilizing multispectral CaSSIS and hyperspectral CRISM data, we investigated opal-bearing deposits in Oxia Planum, the future landing site of the ExoMars “Rosalind Franklin” rover, in order to further assess the region's aqueous geology and astrobiological potential. Additionally, we used CaSSIS color band ratio composites to expand the CRISM data and identify discrete deposits of hydrated silica throughout the sedimentary fan stratigraphy, and identify potential opal-bearing deposits within the Rosalind Franklin landing ellipses. We have detected opal-bearing material in two main physiogeographic regions of Oxia Planum: (a) stratigraphically between the clay-bearing plains and the overlying sedimentary fan, and (b) in discrete outcrops in topographic lows south of the fan deposits. Amorphous opal, likely derived from weathering processes, is the dominant form of hydrated silica in Oxia Planum. Whilst a detrital origin for the hydrated silica-bearing deposits cannot be conclusively ruled out, an authigenic origin, or one in which opaline silica is concentrated by groundwater or pedogenic silicification processes, remains the most plausible formational hypotheses. These outcrops offer exciting prospects for in situ astrobiological exploration, which will allow for these hypotheses to be tested.