A new study reveals that clay deposits at the ExoMars Rosalind Franklin rover's landing site stretch far beyond earlier estimates, covering an area roughly 600 kilometers across and rising over a kilometer in altitude. One hypothesis suggests a vast ocean, possibly several kilometers deep, once covered the region around four billion years ago.
Clay deposits hint at a wetter, more habitable Mars
Clay minerals require liquid water to form. The discovery of such an extensive clay bed at Oxia Planum, the rover's landing site, points to a time when the Red Planet was much wetter and more hospitable to life. The deposits extend as far as Mawrth Vallis, a site about 300 kilometers away that was also a candidate for landing. Scientists believe the clays hold clues about the water environment in which they formed and could contain traces of past microbial life.
Two scenarios for an ancient water world
Oxia Planum lies in an open basin. One scenario is that the clay deposits were shaped by an immense body of water reaching several kilometers in depth. Another possibility is that large amounts of water flooded vast plains from ancient groundwater reservoirs. The ExoMars rover, once its wheels and drill hit the ground, will attempt to verify which scenario is more plausible. The study found that the clay deposits at Oxia Planum formed first, about four billion years ago, predating those at Mawrth Vallis.
Why local scientists care about this discovery
For researchers studying Mars, this finding reframes the timeline of the planet's climate history. "Because the area is so large, we are not talking about a localized occurrence, but rather a regional or global process that would have required immense amounts of water," said Jorge Vago, ExoMars project scientist. The rover will target the oldest deposits in the sequence, making the potential implications for Mars's geology and early climate highly relevant for the mission's search for life. Scientists used data from ESA's Mars Express orbiter and NASA's Mars Reconnaissance Orbiter to examine the mineralogy and reconstruct the rock layering between the two sites.
The Rosalind Franklin rover is set to explore Oxia Planum and investigate whether its clay-rich sediments contain signs of past life. The findings from this mission could help reconstruct the planet's climate and assess whether it was ever truly habitable.
