Bleached Martian rocks suggest Mars may have been warmer and wetter.

NASA's Perseverance rover identified thousands of bleached, kaolinite-rich rocks across Jezero crater, and a December 2025 study reports their chemistry matches Earth clays formed by long-term water exposure; researchers say the rocks' exact source in or beyond the crater is still undetermined.

Perseverance has found thousands of unusually pale, clay-rich rocks scattered across Jezero crater. Scientists report these rocks are rich in kaolinite, a clay that on Earth typically forms when water slowly leaches minerals from rock over long periods. Researchers compared rover data with Earth examples from Southern California and South Africa and found similar chemical signatures. The findings are described in a paper published in December 2025 in Nature Communications Earth & Environment. Key findings: - Perseverance identified several thousand bleached rocks ranging from pebbles to large boulders across Jezero crater. - The rocks contain kaolinite, a clay mineral that on Earth commonly forms in warm, humid environments with prolonged water exposure. - Chemical comparisons with terrestrial kaolinite deposits showed close matches, supporting formation by sustained water alteration rather than volcanic or hydrothermal activity. - Kaolinite-bearing terrains had been seen from orbit before, but these are direct surface observations by the rover. - The study reports no obvious nearby bedrock source; the closest potential source is about 1.2 miles (2 kilometers) away where orbital data show kaolinite in fractured rock. - Researchers note possible transport mechanisms into the crater, including ancient river flow along Neretva Vallis or emplacement by impacts, but the origin remains unresolved. Summary: The presence and chemistry of these bleached, kaolinite-rich rocks add evidence that parts of Mars experienced prolonged water-driven weathering, consistent with a warmer and wetter climate in the distant past. Where the rocks originated and how they arrived at Jezero crater is undetermined at this time, and researchers are continuing to investigate possible source areas and transport processes.