Constraining the spectral behavior of the clay-bearing outcrops in Oxia Planum, the landing site for ExoMars “Rosalind Franklin” rover

Abstract

Oxia Planum (335.5°E, 18.2°N) is selected as the landing site for ExoMars rover mission (ESA/Roscosmos), where the “Rosalind Franklin” rover is scheduled to land in the decade. The region reveals several extensive clay-bearing outcrops recently exhumed, where biosignatures are possibly preserved. The objectives of the mission are to search for organics and investigate traces of past or extant life on Mars. Preliminary surveys of these outcrops show infrared absorptions typical of Fe,Mg-rich clays in the 1.0–2.6 μm range (1.4, 1.9, 2.3 and 2.4 μm) and an additional absorption at 2.5 μm implying a possible mixture with other mineral phase(s). Here we provide a detailed description of absorptions of the clay-rich materials detected in Oxia Planum, and map their strength and distribution throughout the region using hyperspectral data gathered by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard NASA's Mars Reconnaissance Orbiter (MRO) mission. Our analysis suggests that the Fe,Mg-rich clays identified in Oxia Planum mainly correspond to either Fe-bearing saponites (e.g., Griffithite) or vermiculite ores (i.e., vermiculite associated with a hydrobiotite component). Conversely, large clay-bearing outcrops found in the catchment area (337°E, 16.7°N) are rather consistent with nontronites in association with Al-rich clays and kaolins, in agreement with previous identification in the Mawrth Vallis – west Arabia Terra province. Presence of Fe,Ca-rich carbonates is recognized with the absorption near 2.53 μm and the observation of a broad peak in the 3–4 μm range, supporting their co-occurrence with the clays in Oxia Planum and its catchment area. Although we favor a pedogenesis alteration for the clays found in the catchment area, the origin of those studied in Oxia's basin remains enigmatic, where alternative scenarios could be either lacustrine and deltaic sedimentation, groundwater circulation, or even hydrothermal fluid circulation. Future in-situ measurements by “Rosalind Franklin” rover will indubitably provide new insights on the mineralogical diversity seen in the region and their origins.