NASA’s Perseverance rover has found that rocks in Mars’ Jezero Crater were altered by water three separate times. The finding rewrites the crater’s water history.

The study, published in Communications Earth and Environment, rests on more than 185 bedrock analyses by the rover’s SuperCam instrument. Lead author Candice Bedford of Purdue University mapped the chemical changes across the crater’s Margin Unit.

First, carbon-dioxide-rich groundwater reacted with olivine rock, leaving carbonate deposits in cracks. Later, lake water or shifting groundwater deposited silica in rocks below the ancient shoreline.

The third episode was the most surprising. Veins about 25 centimetres thick contain calcium sulfate and fluorite. Fluorite typically forms when hot water moves through volcanic rock, pointing to a later hydrothermal system.

On Earth, olivine-water reactions can release hydrogen, a possible energy source for microbes. Carbonate and silica also preserve traces of past life. The researchers could not yet fix the ages of the three episodes.