You’d expect a crater once filled with an ancient lake to tell a fairly straightforward story. Instead, NASA’s Perseverance rover has detected traces of the existence of at least three different events of water-rock interaction on the Margin Unit, which is an area located on the edge of the Jezero Crater, including one that involved hot groundwater under the surface.
Based on orbiters’ images, it was expected that the rover would discover sedimentary rocks that formed around the shoreline of an ancient lake. Instead, it discovered igneous rocks that formed from lava or volcanoes.
It turns out that the surprising geology, described in a study published in 2026 by Candice Bedford, research scientist at Purdue University, contains traces of water activity far more complicated than initially thought.
SuperCam on the Perseverance rover was used to study more than 185 targets in the Margin Unit. The first event is related to COâ‚‚-rich groundwater and the interaction of the olivine with this water, which resulted in the formation of carbonates in rock fractures.
The second event seems to be connected to Jezero’s ancient lake, as silica deposits are formed that are typical for the rocks underwater.
The third, high-temperature event formed the veins of Ca-sulphate and fluorite in the eastern Margin Unit.
Hydrothermal systems such as this one have been known to provide conditions for the presence of microbial life on Earth, and that is why scientists who study habitability on Mars are fascinated by the third event.
The sequence of events can be determined, but the exact timing of each event has not been determined yet.
According to Bedford, Jezero crater lies within one of the biggest carbonate outcrops on Mars, and therefore results from this one location can give insights into the planet’s history as a whole.
“Mars never stops surprising you,” she said. “The orbital information almost never matches the rover information.”
The study, published September 21 in Communications Earth & Environment, positions the Margin Unit as a genuine crossroads of groundwater, surface water, and heated fluids rather than a simple lakeshore.
