Outstanding Mars Science questions from the investigation of Oxia Planum, the landing site of Exomars rover mission.

Abstract:

The European Space Agency (ESA) and Roscosmos ExoMars Program will launch the “Rosalind Franklin” rover in 2022. The goals of the mission are to search for signs of past and present life on Mars, to investigate the water/geochemical environment as a function of depth in the shallow subsurface, and to characterize the surface environment. Oxia Planum, the landing site of this mission, is a 200-km wide, low relief terrain located on the crustal dichotomy, within the southwest margin of Arabia Terra and characterized by Noachian hydrous clay-bearing bedrock units. The landing site records the action of at least two distinct, ancient aqueous environments: 1) a first phase leading to the deposition and alteration of about 100-m thick, layered, hydrous clays possibly in a sedimentary context and 2) a latter phase with a chemically-active fluvio-deltaic system post-dating the initial, widespread clay-rich, layered unit.

Hereafter, we list major questions regarding Oxia Planum and Mars’ early history that we plan to address utilizing orbital data and then test through detailed rover investigations. Where do the Oxia planum deposits fit in the overall evolution of Mars, especially in relation to major Noachian events, such as the giant basin-forming impacts (e.g. Chryse, Isidis)? Was the site associated with a large, standing body of water that may have once filled Chryse Planitia? What exactly is the origin and mode of alteration for Oxia clay bearing unit ? Was the intense volcanic and tectonic activity associated with Tharsis bulge formation recorded in Oxia Planum; if so, how? What is the exhumation history of the landing site?

Gleaning answers to the above questions will be crucial to understand ancient Mars history and the role of water in shaping the surface rock record. The answer to each of these questions has a strong impact on the ability of Oxia Planum to have first accumulated, then sequestered and protected organic matter, or even to have been an ancient habitat. As such, its study will provide the necessary geological context framework for any possible candidate biosignatures that Rosalind Franklin may find.