OXIA PLANUM — The ExoMars Rosalind Franklin rover is scheduled to land at Oxia Planum on Mars to investigate newly identified ancient clay deposits and a paleosurface. These features suggest a large-scale, water-driven geological process occurred approximately four billion years ago.
Researchers analyzed the mineral composition of the region using the OMEGA instrument on ESA's Mars Express orbiter and the CRISM instrument on NASA's Mars Reconnaissance Orbiter. The analysis showed that clay deposits in the Oxia Planum region extend beyond previously estimated boundaries, spanning approximately 600 kilometers in width and reaching elevations over one kilometer. These deposits extend about 300 kilometers from the site to the Mawrth Vallis region, and orbital data indicates both locations contain similar mineral layers.
A paleosurface, an ancient exposed geological layer cratered and buried by younger deposits, was identified at the boundary between two primary clay-bearing units at both Oxia Planum and Mawrth Vallis. This paleosurface indicates a historical pause in sediment deposition, followed by shifts in water chemistry and mineral composition. A scientific hypothesis proposes that a large body of water previously covered the landing site, as clay minerals require liquid water to form. The clay deposits may have been shaped by a water body several kilometers deep around four billion years ago.
Jorge Vago, ExoMars project scientist, stated, "Because the area is so large, we are not talking about a localised occurrence, but rather a regional or global process that would have required immense amounts of water. We are targeting the oldest deposits in the sequence, which makes the potential implications for the geology and early climate of Mars very relevant for the Rosalind Franklin mission in its search for life." Inés Torres Auré, lead author from the University of Lyon, said, "We now have a new timeline: Oxia Planum's clays formed first, about four billion years ago, predating those at Mawrth Vallis. By landing at Oxia Planum, we'll uncover a large-scale process that shaped ancient clays across Mars." Torres Auré noted the team identified a pause in deposition, implying a period of minimal surface activity followed by changes in water chemistry and mineralogy in both regions. She added that preparation for the rover's arrival includes mapping the full extent of the deposits, identifying additional pauses in formation, and quantifying their duration.
The rover is equipped with cameras, spectrometers, ground-penetrating radar, an analytical laboratory, and a drill capable of reaching two meters below the surface.