Scientists have discovered that huge clay deposits near the landing site of the upcoming ExoMars Rosalind Franklin rover are much larger than previously thought.
The finding strengthens the idea that large amounts of water once existed on Mars and may even suggest that a vast ocean covered part of the planet around 4 billion years ago.
The Rosalind Franklin rover, developed as part of the ExoMars mission, is scheduled to land in a region called Oxia Planum.
Scientists chose this location because it contains clay-rich rocks that formed in the presence of liquid water.
Since water is considered one of the key ingredients for life, these ancient deposits could preserve important evidence about whether life ever existed on Mars.
Clay minerals are especially valuable to researchers because they can trap and preserve chemical and biological traces for billions of years.
Studying them can help scientists understand what Mars was like when it was warmer, wetter, and potentially more suitable for life.
A new study has revealed that the clay deposits at Oxia Planum stretch much farther than expected. Researchers found that these deposits extend all the way to Mawrth Vallis, another scientifically important region located about 300 kilometers away.
Together, the clay-rich area spans roughly 600 kilometers and rises more than one kilometer in elevation.
The enormous size of the deposits suggests that they were formed by a major geological process rather than a small local event.
One possibility is that a deep ocean once covered the region. Because Oxia Planum sits inside a large open basin, scientists believe it may have been submerged beneath water that reached several kilometers in depth.
Another possibility is that massive amounts of groundwater emerged from underground reservoirs and flooded the surrounding plains. Either way, the findings indicate that water played a significant role in shaping the Martian landscape.
Jorge Vago, ExoMars project scientist, said the deposits point to a regional or even global process that required enormous quantities of water. Because the rover will investigate some of the oldest clay deposits on Mars, its discoveries could greatly improve scientists’ understanding of the planet’s early climate and geology.
The study also helps establish a clearer timeline of events on ancient Mars. Researchers found evidence that the clays at Oxia Planum formed before those at Mawrth Vallis. According to lead author Inés Torres Auré from the University of Lyon in France, this means the rover will be able to investigate one of the earliest large-scale processes that shaped the Martian surface.
To make the discovery, scientists analyzed data collected by two orbiting spacecraft: the European Space Agency’s Mars Express and NASA’s Mars Reconnaissance Orbiter. By studying the mineral composition and rock layers across the region, they found that Oxia Planum and Mawrth Vallis share remarkably similar geological structures.
The team also identified what is known as a paleosurface—an ancient landscape that was once exposed to the environment before being buried beneath younger deposits. This buried surface contains many impact craters, showing that there was a period when little new material was being deposited.
Researchers believe this pause was followed by a major change in water chemistry and mineral formation across both regions. The reason for this shift remains a mystery, but it may provide important clues about changes in Mars’s environment billions of years ago.
The Rosalind Franklin rover is designed specifically to investigate questions like these. It carries cameras, spectrometers, a ground-penetrating radar system, and a miniature laboratory. Most importantly, it can drill up to two meters below the surface, allowing it to reach samples that have been protected from harsh radiation and weathering for billions of years.
Scientists hope the rover will confirm what orbiters have observed from space and provide direct evidence about how these clay deposits formed. If Mars once had a warm, nutrient-rich seabed, it may have offered suitable conditions for microbial life.
The rover’s onboard laboratory will carefully examine collected samples for possible biological signatures. Meanwhile, researchers continue to map the clay deposits and investigate their history so they can better understand Mars before the rover begins its exploration.
If successful, the mission could provide some of the strongest evidence yet about whether ancient Mars was once a world capable of supporting life.
