Photo: nature.com
NASA’s Perseverance rover has discovered light fragments of kaolinite in Jezero Crater that could only have formed under a prolonged rainy climate. Scientists compared these Martian rocks with similar samples on Earth and concluded that Mars once had conditions potentially suitable for life, Phys reports.
In a study published in Communications Earth & Environment, an international team of researchers described fragments of kaolinite — a white, aluminum-rich clay — detected by Perseverance in Jezero Crater. On Earth, this mineral forms only after long-term leaching of other components in wet, rainy environments.
“It takes so much water that we think this may be evidence of an ancient warmer and wetter climate where rain fell for millions of years,” said Briony Horgan, a professor of planetary science at Purdue University. Lead author Adrian Broz noted that this type of clay is most common in tropical regions on Earth. “When you see kaolinite in a place like Mars, a barren, cold environment with no liquid water on the surface, it tells us there was once much more water than today,” he added.
Researchers compared the Martian samples with rocks from California and South Africa and found significant similarities. The kaolinite fragments, ranging from pebbles to boulders, add a new layer to the debate over Mars’ ancient climate.
Initial analyses using the rover’s SuperCam and Mastcam-Z confirmed their similarity to terrestrial rocks formed under warm and wet conditions. These findings help reconstruct how the planet shifted from past wet periods to its modern dry landscape. Despite the large number of clay fragments, there are no nearby bedrock exposures they could have originated from. Orbital images show large kaolinite outcrops elsewhere on Mars, but they remain out of reach for direct sampling.
“They might have been washed into Jezero’s ancient lake by the river that formed its delta, or they could have been ejected by an impact and scattered there. We’re not entirely sure,” Horgan said.
The study also evaluated a potential hydrothermal origin — involving hot water — but chemical analysis pointed instead to long-term rainfall weathering at low temperatures. The team used data from several Earth locations to compare these processes. Kaolinite on Mars serves as a kind of geological time capsule that may preserve clues about environmental conditions billions of years ago. “All life uses water,” Broz emphasized. “So having rocks formed by sustained rainfall suggests a potentially habitable environment.”
“When we think about the possibility that these rocks on Mars represent a rainfall-driven environment, it’s truly an incredible, habitable place where life could have thrived if it ever existed there,” he said.
Perseverance continues collecting samples in Jezero Crater, once home to a large lake roughly twice the size of Lake Tahoe. Scientists hope future analyses will help determine when and how Mars lost its water and became the barren desert we see today.
