Bleached Kaolinite Rocks on Mars Suggest Long-Term Rain and a Potentially Habitable Past

NASA’s Perseverance rover has discovered bleached, white rock fragments on Mars that researchers interpret as kaolinite — a clay mineral typically formed by prolonged rainfall and sustained humidity on Earth. The finding adds to growing evidence that parts of ancient Mars experienced warm, wet conditions capable of altering rocks the way tropical weathering does on our planet.

A team that analyzed thousands of fragments published their results in Communications Earth & Environment in December. The researchers say the fragments range from pebble-sized pieces to boulders and closely match kaolinite-bearing rocks found near San Diego and in regions of South Africa.

What the Rocks Reveal

Kaolinite is an aluminum-rich clay that forms when other minerals are leached away by long-term exposure to water and humidity — processes that on Earth occur over millions of years in tropical, rainy climates. Finding this mineral on Mars suggests that some locations underwent sustained alteration by liquid water, not just brief wet events.

“It tells us that there was once a lot more water than there is today,” said Adrian Broz, lead author of the study and a planetary scientist at Purdue University.

Rowan Horgan, a long-term planner on the Perseverance mission, noted from orbital observations that rocks like these are hard to form and require extensive water: “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.”

Where the Fragments Came From

The fragments were found in and around Jezero Crater, a basin long interpreted as the site of an ancient lake. Because no major kaolinite outcrop lies immediately adjacent to the find sites, the team suggests two plausible transport mechanisms: the pieces were either washed into the crater by ancient rivers and runoff, or they were excavated and scattered across the landscape by an impact event. Orbital spectral data also reveal other kaolinite-rich outcrops elsewhere on Mars, supporting a broader distribution of this alteration product.

Why This Matters

The bleached rocks act like a time capsule, preserving clues about environmental conditions billions of years ago and helping scientists reconstruct how Mars transitioned from a wetter world to the cold, dry planet we see today. Because liquid water is a fundamental requirement for life as we know it, evidence for long-lived, rainfall-driven environments increases the possibility that ancient Mars could once have supported habitable environments.

Perseverance — launched in 2020 and arriving at Jezero Crater in February 2021 after a roughly 200-day, 300-million-mile journey — has spent years collecting geological context and samples. By late 2024 the rover began exploring the crater rim, continuing its search for rocks that might preserve biosignatures or other traces of past habitability.

What Comes Next: Researchers will continue to map kaolinite occurrences from orbit, study returned samples (when available), and compare Martian fragments with terrestrial analogs to better constrain the timing and duration of the wet conditions that produced them.

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Purdue University research into scattered kaolinite rocks on Mars’ surface shows the dry, dusty planet could have featured a rain-heavy climate billions of years ago.