Spectral Analysis of Clay-bearing Outcrops in Northern Xanthe Terra, Mars: Comparison with Oxia Planum, the Landing Site for the ExoMars Rover Mission

Abstract

Clay minerals detected on Mars are valuable targets to seek traces of life on the planet, where biosignatures might be preserved. Here, we report an in-depth spectral analysis of clay-rich outcrops identified in northern Xanthe Terra (300°–320° E, 10°–20° N). We focused particularly on the absorptions centered in the 1.0–2.6 μm spectral range to (1) constrain the mineralogy of the clay outcrops, (2) map their strength and distribution throughout the region, and thus (3) develop a better understanding of the geologic environment at circum–Chryse Planitia. We then compared the infrared signatures in Xanthe Terra and Oxia Planum. Like in Oxia Planum, Xanthe’s clays are consistent with either Fe-bearing saponites or vermiculites. However, the spectral signatures in Xanthe are weaker relative to Oxia Planum, perhaps due to significant dust cover in the region. Besides the spectral signatures, northern Xanthe Terra displays several morphological features similar to Oxia Planum, indicating long-lasting aqueous activity (fluvial channels and fan deltas). Clays found at the fan deltas could be detrital (fluvial transport) or authigenic (lacustrine or deltaic sedimentation), while the origin of clays seen elsewhere on the surrounding plateaus remains undetermined. Oxia Planum has been selected as the landing site for ESA’s ExoMars “Rosalind Franklin” rover, where its instruments will search for signs of life and constrain the nature and origin of the clays. This exploration will indubitably provide new clues on the clays found in the circum-Chryse basin.