NASA's Perseverance rover has discovered bright white rocks made of kaolinite clay in Jezero Crater, suggesting Mars once experienced millions of years of rainfall in warm, humid conditions. These aluminum-rich clays, similar to those formed in Earth's tropical rainforests, imply the planet had abundant water and potentially habitable environments long ago. The scattered rocks puzzle scientists about their origins, possibly from floods or impacts.
Small, pale rocks scattered across Mars' surface have provided compelling evidence of a wetter past for the Red Planet. NASA's Perseverance rover, which landed in Jezero Crater in February 2021, identified these as kaolinite, an aluminum-rich clay. On Earth, kaolinite forms through prolonged chemical weathering from heavy rainfall in warm, wet climates, such as rainforests, a process that takes millions of years.
The discovery, detailed in a study published in Communications Earth & Environment, was led by Adrian Broz, a postdoctoral researcher at Purdue University, under Briony Horgan, a professor of planetary science and mission planner for Perseverance. "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," Horgan said.
The rover's SuperCam and Mastcam-Z instruments analyzed the rocks, ranging from pebbles to boulders, revealing chemical signatures matching Earth samples from near San Diego, California, and South Africa. These comparisons ruled out hydrothermal formation, favoring surface rainfall as the cause. Broz noted, "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."
Jezero Crater, once home to a lake about twice the size of Lake Tahoe, shows no nearby source for the kaolinite, leading to theories of river transport or asteroid impacts. "They're clearly recording an incredible water event, but where did they come from?" Horgan questioned. "Maybe they were washed into Jezero's lake by the river that formed the delta, or maybe they were thrown into Jezero by an impact."
Such findings offer insights into Mars' transition from a potentially habitable world to its current dry state, preserving clues about ancient environments that might have supported life. "All life uses water," Broz emphasized. "That is a really incredible, habitable place where life could have thrived if it were ever on Mars."
