Mars Was Once a Tropical Oasis, New Study Suggests

Evidence of rain-driven climate on Mars has been found in bleached rocks scattered across Jezero Crater.

Small, pale spots on the reddish-orange landscape of Mars have turned out to be a new clue that parts of the planet may once have hosted wet, oasis-like environments with humid conditions and rainfall similar to tropical regions on Earth.

NASA’s Perseverance rover identified these features as white, aluminum-rich kaolinite clay. On Earth, this type of clay develops when long periods of heavy rain gradually remove other minerals from rocks and sediment, leaving behind the purified material.

Details of the discovery were recently published in the scientific journal Communications Earth & Environment. The study was led by Adrian Broz, a Purdue University postdoctoral research associate working in the lab of Briony Horgan, who serves as a long-term planner for NASA’s Mars Perseverance mission and is a professor of planetary science in Purdue’s Department of Earth, Atmospheric, and Planetary Sciences in the College of Science.

A Rare Martian Mineral and Its Implications

“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.

Fragments of kaolinite on Mars, ranging from tiny pebbles to large boulders, have become a new piece of evidence in the broader scientific discussion about what the planet’s climate was like billions of years in the past. Early analyses using the rover’s SuperCam and Mastcam-Z instruments allowed researchers to compare these Martian samples with their counterparts on Earth. These comparisons may help reveal the environmental conditions Mars once experienced and provide clues about how it eventually became the dry world it is today.

According to Horgan, the kaolinite raises another puzzle. The light-colored rocks appear along Perseverance’s route even though there is no obvious nearby source. The rover has been traveling across Jezero crater since its landing in February 2021, an area that once held a lake about twice as large as Lake Tahoe.

Searching for the Source

“They’re clearly recording an incredible water event, but where did they come from?” Horgan said. “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, and they’re just scattered there. We’re not totally sure.”

Satellite imagery has spotted large outcroppings of kaolinite in other areas of Mars.

“But until we can actually get to these large outcroppings with the rover, these small rocks are our only on-the-ground evidence for how these rocks could have formed,” Horgan said. “And right now the evidence in these rocks really points toward these kinds of ancient warmer and wetter environments.”

Earth Analogs and Martian Mysteries

Broz compared the Martian kaolinite samples examined by Perseverance with rock samples found in locations near San Diego, California, and in South Africa. The rocks from the two planets were a close match.

Aside from a rain-heavy tropical climate, Broz said kaolinite on Earth also forms in a hydrothermal system when hot water is leaching the rock. But that process creates a different chemical signature in the rock than leaching at lower temperatures by rain over thousands to millions of years. He said datasets from three different sites were used to compare the hydrothermal leaching scenario to the Mars rocks.

Rocks on Mars, like the kaolinite, are a similar time capsule, potentially holding information from billions of years ago about the history of environmental conditions on the planet.

“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.”

Reference: “Alteration history of aluminum-rich rocks at Jezero crater, Mars” by A. P. Broz, B. H. N. Horgan, C. Bedford, C. Royer, H. Manelski, S. Connell, R. C. Wiens, E. C. Cardarelli, J. M. Madariaga, L. Mandon, A. Klidaras, M. Bramble, B. Kathir, O. Forni, John Carter, E. Dehouck, C. Quantin-Nataf, J. R. Johnson, J. I. Nuñez, E. Hausrath, U. Wolf, E. A. Cloutis, P. Beck, J. F. Bell, J. I. Simon and A. Cousin, 1 December 2025, Communications Earth & Environment.
DOI: 10.1038/s43247-025-02856-3

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