At the boundary between the two main clay-bearing units, the team also identified a paleosurface: a remnant of an ancient, exposed surface that was heavily cratered and later covered by younger deposits. This paleosurface marks a pause in sedimentation, followed by a shift in water chemistry and mineralogy across both sites.

These results align with recent studies suggesting an intermittently wet climate on early Mars.

“We have identified a pause in deposition, which is quite puzzling because it implies a period of minimal surface activity (except for meteorite bombardment), followed by a shift in water chemistry and mineralogy in both Oxia Planum and Mawrth Vallis,” adds Inés.

Guided by this finding, the Rosalind Franklin rover is well equipped to confirm the orbiters’ results from the surface and help reconstruct Mars’ early water history.