NASA's Perseverance rover identified light-colored rocks in Jezero crater that consist of white, aluminum-rich kaolinite clay. These rocks formed after prolonged exposure to water leached other minerals from parent rocks and sediments. The process required millions of years of rainfall in a humid environment.
Perseverance's SuperCam and Mastcam-Z instruments analyzed the kaolinite fragment Los Angeles CA (SPX) Dec 03, 2025
NASA's Perseverance rover identified light-colored rocks in Jezero crater that consist of white, aluminum-rich kaolinite clay. These rocks formed after prolonged exposure to water leached other minerals from parent rocks and sediments. The process required millions of years of rainfall in a humid environment.
Perseverance's SuperCam and Mastcam-Z instruments analyzed the kaolinite fragments, which range from pebbles to boulders. Researchers compared these samples to Earth rocks from sites near San Diego, California, and in South Africa. The Martian kaolinite matches formations from rain-driven leaching over extended periods.
Kaolinite occurs on Earth primarily in tropical rainforest settings with heavy rainfall. On Mars, such deposits indicate past conditions with abundant surface water. Satellite images reveal larger kaolinite outcrops elsewhere on the planet, but these small fragments provide the first ground-level data from Jezero.
The crater once held a lake roughly twice the size of Lake Tahoe, and a river likely deposited the rocks via the delta. An impact event may also have scattered them across the area. The absence of a nearby major outcrop adds uncertainty to their origin.
"Elsewhere on Mars, rocks like these are probably some of the most important outcrops we've seen from orbit because they are just so hard to form," Horgan said. "You need so much water that we think these could be evidence of an ancient warmer and wetter climate where there was rain falling for millions of years."
Broz said tropical climates like rainforests are the most common environments to find kaolinite clay on Earth.
"So when you see kaolinite on a place like Mars, where it's barren, cold and with certainly no liquid water at the surface, it tells us that there was once a lot more water than there is today," said Broz, a postdoctoral collaborator on the Perseverance rover.
Hydrothermal processes can form kaolinite, but they produce a distinct chemical signature unlike the rain-leached type observed here. Datasets from three Earth sites confirmed the low-temperature, rainfall origin for the Mars samples. These rocks preserve environmental conditions from billions of years ago.
"All life uses water," Broz said. "So when we think about the possibility of these rocks on Mars representing a rainfall-driven environment, that is a really incredible, habitable place where life could have thrived if it were ever on Mars."
Research Report:Alteration history of aluminum-rich rocks at Jezero crater, Mars
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