Morphological and Spectral Diversity of the Clay-Bearing Unit at the ExoMars Landing Site Oxia Planum

Abstract

The European Space Agency and Roscosmos' ExoMars rover mission, which is planned to land in the Oxia Planum region, will be dedicated to exobiology studies at the surface and subsurface of Mars. Oxia Planum is a clay-bearing site that has preserved evidence of long-term interaction with water during the Noachian era. Fe/ Mg-rich phyllosilicates have previously been shown to occur extensively throughout the landing area. Here, we analyze data from the High Resolution Imaging Science Experiment (HiRISE) and from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments onboard NASA's Mars Reconnaissance Orbiter and the Colour and Stereo Surface Imaging System (CaSSIS) onboard ESA's Trace Gas Orbiter to characterize, at a high spatial resolution, the morphological and spectral variability of Oxia Planum's surface deposits. Two main types of bedrocks are identified within the clay-bearing, fractured unit observed throughout the landing site: (1) an orange type in HiRISE correlated with the strongest detections of secondary minerals (dominated by Fe/Mg-rich clay minerals) with, in some locations, an additional spectral absorption near 2.5 mm, suggesting the mixture with an additional mineral, plausibly carbonate or another type of clay mineral; (2) a more bluish bedrock associated with weaker detections of secondary minerals, which exhibits at certain locations a *1 mm broad absorption feature consistent with olivine. Coanalysis of the same terrains with the recently acquired CaSSIS images confirms the variability in the color and spectral properties of the fractured unit. Of interest for the ExoMars mission, both types of bedrocks are extensively outcropping in the Oxia Planum region, and the one corresponding to the most intense spectral signals of clay minerals (the primary scientific target) is well exposed within the landing area, including near its center.

Mineralogical and Spectral (Near-Infrared) Characterization of Fe-Rich Vermiculite-Bearing Terrestrial Deposits and Constraints for Mineralogy of Oxia Planum, ExoMars 2022 Landing Site

“…The origin of such voluminous Fe,Mg-phyllosilicate deposits is not yet fully understood. Layering within the deposits reported by Mandon et al (2021) and draping of the topography documented by Quantin-Nataf et al (2021) suggest that the bedrock phyllosilicates formed in a subaqueous environment (palustrine, lacustrine, or marine) or in subaerial conditions compatible with airborne volcaniclastics altered by pedogenesis or via aeolian deposits. Furthermore, geomorphological features indicate that postdating deposition of the bedrock unit, a separate aqueous event occurred in this place, most likely connected to fluvial and deltaic activity (Turner and Bridges, 2017;Quantin-Nataf et al, 2021).…”

“…An automated correcting mode on the instrument was used to better correct the OH signatures due to ambient air (slightly noisy data are spotted around 1.4, 1.9, and 2.7 mm). Noise present near 2.6 mm does not permit verification of absorption at 2.5 mm such as the one reported to exist locally at Oxia by Mandon et al (2021). The spectra were processed using a procedure of continuum removal from 1.00 to 2.60 mm to compare our laboratory results with CRISM and OMEGA spectra, which are best interpreted by using this part of the signal.…”

“…Based on geomorphological evidence, bedrock clay deposits at Oxia Planum could have formed either in a subaqueous environment (palustrine, lacustrine, or marine) or in subaerial conditions compatible with airborne volcaniclastics altered by pedogenesis or aeolian deposits (Carter et al, 2016;Turner and Bridges, 2017;Mandon et al, 2021;Quantin-Nataf et al, 2021). Deep burial and metamorphic conditions do not seem likely (Quantin-Nataf et al, 2021).…”

“…Remote sensing observations were used to choose a landing ellipse (*19 • 120 km) comprising 70% of middleto late-Noachian (>3.9 Ga) in age, stratified bedrock deposits rich in hydrous Fe,Mg-clays (Carter et al, 2016;Turner and Bridges, 2017;Mandon et al, 2021;Quantin-Nataf et al, 2021). The bedrock unit is one of the largest exposures of this type on Mars and is more than 50 m thick (Quantin-Nataf et al, 2021), although the exact amount of clays in this region is not fully recognized from the orbit.…”

Subsurface Thermal Modeling of Oxia Planum, Landing Site of ExoMars 2022

“…is location has been identified in Oxia Planum, a 200 km-wide low-relief terrain [4], at a latitude of about 18 ∘ . Oxia Planum shows evidence of subaqueous episodes being characterized by hydrous claybearing bedrock units and layered outcrops [4][5][6]. e entire area of Oxia is undergoing erosion, attested by morphology (inverted features) and crater statistics [4].…”