On Mars, Perseverance finds traces of three episodes of water at the edge of Jezero crater

The facts

On Monday 21 September 2026, the journal Communications Earth & Environment published a study of the “Margin Unit”, a strip of terrain running along the inner edge of Jezero crater, on Mars. Led by Candice Bedford, a researcher at Purdue University (Indiana), it draws on data from NASA’s Perseverance rover, which reached this area in September 2023.

The rocks there bear the marks of at least three episodes of water. First, groundwater laden with carbon dioxide reacted with the olivine in the rock and filled its fractures with carbonates. These veins, harder than the surrounding rock, now form ridges. Next, silica was deposited between the grains, especially in rocks lying below the former level of the crater’s lake; this episode may be linked to the lake itself, or to a change in the groundwater. Finally, at one spot in the eastern part, veins about 25 centimetres thick contain calcium sulphate and fluorite. The latter mineral usually forms when hot water circulates through volcanic rocks: the sign of a hydrothermal episode.

The team knows the order of these episodes, but not their age.

The context

Jezero once held a lake. Seen from orbit, its rim showed strong signals of carbonates, minerals that on Earth often form in lakes or shallow seas. Scientists therefore expected to find sedimentary rocks, made of layers of sand and mud deposited over time.

The rover found something else: an igneous rock rich in olivine. Higher up, it is crystalline and coarse-grained, and shows almost no trace of water. It formed in a pocket of magma that cooled slowly at depth, before being exposed by erosion.

The key tool in the study is SuperCam, mounted at the top of the rover’s mast. Its laser targets rocks up to 6.5 metres away; the light from the tiny cloud of vaporised material reveals their chemical composition. More than 185 targets were analysed in this way, over about 265 metres of elevation. SuperCam is co-led by Purdue University, Los Alamos National Laboratory and, in France, IRAP and CNES, in Toulouse.

Why it matters

According to Candice Bedford, Jezero lies within one of the largest carbonate outcrops on Mars: what happened there therefore sheds light on the history of water well beyond the crater. Carbonates and silica are also of interest in the search for traces of past life, because they can preserve its imprint.

Above all, the study shows that the lake’s edge was a crossroads for different flows of water, rather than the simple shoreline imagined from orbital images. “Mars constantly throws surprises at you,” the researcher sums up. Perseverance collected rock samples in the Margin Unit.

Archive note

• Study published on 21 September 2026 in Communications Earth & Environment, led by Candice Bedford (Purdue University).
• More than 185 rock targets analysed by laser with the SuperCam instrument, co-led in France by IRAP and CNES.
• Three successive episodes of water, the last one hydrothermal; their age remains unknown.