A Martian rock formation that looked like an ancient shoreline from space now appears to preserve a much more astonishing water history.
Since 2021, NASA‘s Perseverance rover has explored Jezero crater, a 28-mile-wide basin on Mars where rivers once fed a lake. Scientists had hoped to find sedimentary rocks along the crater’s edge — a clue that would support the lakeshore prediction.
But, in a twist, the rover discovered these rocks are igneous, meaning their origins are volcanic and not formed by the lake. Water, the rover found, had actually soaked the rocks at least three separate times, in three different ways. This new understanding of the Jezero landmark, dubbed the “margin unit,” gives scientists a fuller picture of ancient Mars, revealing a planet where water kept finding new ways to move through the landscape.
Though the rover data didn’t reveal evidence of life, they did show an abundance of carbonates — minerals known to be good at locking in traces of past microbes. On Earth, these minerals often form in shallow oceans and lakes that host life.
“Jezero Crater sits inside one of the largest exposures of carbonate on Mars,” said Candice Bedford, a scientist at Purdue University in Indiana, in a statement. “What we learn here reaches well beyond this crater.”
For the study, Perseverance explored an elevation range of about 870 feet across the margin unit. It used its SuperCam instrument to identify minerals in rocks based on the light they reflect. All told, the rover examined 185 rocks. The paper analyzing this data, led by Bedford, appears in the journal Communications Earth & Environment.
To scientists, the biggest surprise from the study may be that this strip of land didn’t initially form at the bottom of a lake. It began earlier when magma deep underground cooled. As its temperature dropped, it formed olivine, a mineral common in volcanic rocks. Much later, after erosion exposed the rocks at the surface, carbon dioxide–rich groundwater began to seep into their cracks. That interaction led to threads of carbonate minerals. Over time, the surrounding rock wore away, leaving only the crack fillers standing.
Credit: NASA / JPL-Caltech
Then, researchers found evidence of a later episode of water that could have been from the lake.
“Turning olivine into carbonate can leave silica behind, and we see more of that silica in rocks that sat below the water line,” said Eleni Ravanis, a co-author and planetary scientist at the University of Hawaii at Manoa.
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The rocks preserve other signs of the lake. In some places, water appears to have broken and moved pieces. The researchers found layered rocks that could reflect activity along the lake’s shore, as well as a jumbled deposit that resembles mud and rocks carried by a rush of water.
In one particular part of the strip of land, Perseverance detected mineral veins of calcium sulfate and fluorite. Those minerals hint that the site experienced yet a third wet episode involving hot water passing through the volcanic rocks, a bit like a hot spring system.
This water history matters in the search for ancient life. Scientists want to know what kind of water existed, what chemicals it carried, and whether it created environments where microbes could get the necessary food to live. The Perseverance team can determine the order of these ancient water episodes, but not when they happened.
Regardless, a place that was repeatedly wet gives life more chances to emerge and more chances to leave behind evidence. The rover has collected samples from the formation, which could shed more light on the environment if NASA can figure out how to get the extraterrestrial material back to Earth. Congress killed future funding for the Mars Sample Return mission in January.
“If there is one thing I have learned after 10 years working with Mars rovers, it is that Mars constantly throws surprises at you,” Bedford said. “It is very rare that things are as we expect them to be from orbital data.”
