NASA’s Perseverance spacecraft has identified thousands of light-toned rock fragments, also known as floating rocks, several of which exhibit spectral characteristics of an aluminum-rich clay mineral known as kaolinite. To understand their origins, planetary scientists utilized data from Perseverance’s SuperCam and Mastcam-Z instruments to analyze the chemistry and reflectance spectra of the floating rocks in relation to deeply weathered paleosols (ancient soils) and hydrothermal kaolin deposits recorded in Earth’s geological archives. The increased levels of aluminum and titanium, along with the reduced amounts of iron and magnesium, differentiate these rocks from hydrothermal deposits, aligning them more closely with the bleached layers of paleosoils formed during periods of significant rainfall in Earth’s past greenhouse climates. Thus, these rocks may signify some of the most aqueous periods in Mars’ history.
Mastcam-Z landscape and multispectral images of light-toned float rocks atop the Jezero Crater Margin Unit near the Hans Amundson Memorial Works (Sol 912). It shows the spectral diversity of this material. Image credit: Broz others., doi: 10.1038/s43247-025-02856-3.
“Rocks like these are likely among the most significant outcrops we’ve observed from orbit because their formation is challenging to replicate elsewhere on Mars,” stated Dr. Bryony Hogan, Perseverance’s long-term planner and a researcher at Purdue University.
“Given that these require substantial water, we believe they could be indicative of an ancient, warmer, wetter climate that experienced prolonged periods of rainfall.”
“Tropical environments, such as rainforests, are where kaolinite clays are predominantly found on Earth,” added Adrian Broz, Ph.D., a postdoctoral researcher at Purdue University.
“Thus, when finding kaolinite on Mars, which is desolate and frigid with no surface liquid water, it suggests that there used to be significantly more water than is present today.”
Kaolinite fragments, varying in size from pebbles to larger rocks, contribute to the ongoing discussion about the climate of Mars billions of years ago.
Initial analyses using the SuperCam and Mastcam-Z instruments have involved comparing kaolinite to analogous rocks on Earth.
Debris from Mars could yield crucial insights into not only the planet’s historical environmental conditions but also how it transitioned to its current desolate state.
“Kaolinite carries its own enigmas,” emphasized Dr. Hogan.
“Currently, there are no significant outcrops nearby that could explain the presence of these light-colored rocks, despite their distribution along the mission’s path since Perseverance’s landing in Jezero Crater in February 2021.”
“This crater once housed a lake that was approximately twice the size of Lake Tahoe.”
“While there are compelling indicators of significant water events, the origin of these rocks remains uncertain.”
“It’s possible they were transported into the Jezero lake by rivers that formed the delta regions, or they may have been ejected into Jezero by a meteorite impact. The complete picture is still unclear.”
Satellite imaging has revealed substantial kaolinite outcrops in various regions of Mars.
“However, until we can physically reach these large outcrops with spacecraft, these small rocks are the only tangible evidence we have regarding their formation,” Dr. Hogan noted.
“Currently, the findings in these rocks suggest a historically warmer and wetter environment.”
Mastcam-Z and SuperCam observations of hydrated layers of aluminum-rich floating rock in Jezero Crater, Mars. Image credit: Broz others., doi: 10.1038/s43247-025-02856-3.
The researchers compared the Martian kaolinite samples studied by Perseverance to rock samples located near San Diego, California, and in South Africa. The similarities between the rocks from both planets were striking.
On Earth, kaolinite forms in both rainy tropical climates and hydrothermal systems where hot water permeates into rocks.
Nonetheless, this process leaves behind chemical signatures that differ from the effects of cold leaching from rain over extended periods.
Scientists evaluated various hydrothermal leaching scenarios against Martian rocks using datasets from three distinct sites.
Rocks like kaolinite from Mars act as time capsules, potentially preserving billions of years of information regarding environmental conditions throughout Earth’s history.
“All life requires water, so if these Martian rocks signify a rainfall-driven environment, that’s an extraordinary indication of a potentially habitable space where life could have flourished on Mars,” stated Dr. Broz.
The team’s paper has been published in the journal Communication Earth and Environment.
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AP Broz others. 2025. Alteration history of aluminum-rich rocks in Mars’ Jezero Crater. Communication Earth and Environment 6,935; doi: 10.1038/s43247-025-02856-3
Source: www.sci.news
