NASA’s Perseverance rover has assembled a compelling mineralogical case that Jezero crater on Mars once sustained a warm, wet climate with rainfall lasting millions of years. Light-colored rocks scattered across the crater floor carry chemical signatures that, on Earth, form almost exclusively under tropical conditions, where heavy rains leach iron and magnesium from bedrock and concentrate aluminum-bearing clays. Combined with carbonates, iron phosphates, and water-altered volcanic rocks found along the rover’s traverse, the evidence suggests Jezero was far more than a cold, dry basin. It may have been a rain-fed lake system with the chemical ingredients to support microbial life.
Bleached Rocks Point to Tropical Rainfall
The strongest thread connecting Jezero to a tropical past comes from a set of light-toned, aluminum-rich float rocks the rover identified on the crater floor. Published in Communications Earth and Environment, the analysis shows these rocks carry kaolin-group signatures, specifically kaolinite and halloysite, with pronounced aluminum-to-titanium enrichment and simultaneous iron and magnesium depletion. That chemical profile is diagnostic: on Earth, kaolinite forms when sustained rainfall percolates through rock, stripping away soluble metals and leaving behind aluminum-rich clays. The process requires abundant liquid water interacting with rock surfaces over geological timescales, not a one-off flood or brief thaw.
Researchers at Purdue University have drawn a direct parallel, noting that kaolinite is most common in tropical climates on Earth and that the bleached rocks scattered across Jezero provide evidence of a rain-driven climate persisting for millions of years. The rocks appear as light-colored dots against the reddish-orange Martian surface, standing out precisely because they have been chemically stripped in a way that cold, arid conditions cannot replicate. This is where the “tropical oasis” framing gains its footing: the mineral assemblage does not merely suggest the presence of water but implies a sustained hydrological cycle with atmospheric moisture, precipitation, and surface runoff carving and leaching the crater’s ancient terrain.
Volcanic Bedrock Transformed by Water and Carbon Dioxide
Kaolinite alone would be striking, but Perseverance has also documented extensive alteration of the volcanic bedrock that lines Jezero’s floor and walls. Coarse-grained olivine-rich igneous rocks across a roughly 10 km traverse and more than 400 m of elevation show pervasive conversion to magnesium- and iron-carbonates, silica, and phyllosilicates. That mineral suite forms when olivine reacts with liquid water charged with dissolved carbon dioxide, a process called carbonation. The sheer spatial extent of this alteration, stretching across kilometers and hundreds of meters of vertical relief, rules out localized groundwater seeps and instead points to a regional aqueous environment where CO₂-rich fluids interacted with rock at scale over long periods of Martian history.
Separately, the U.S. Geological Survey has documented olivine-rich ultramafic float boulders with olivine composition around Fo73, along with high-magnesium orthopyroxene and chromium-rich oxides. These boulders are unusual compared to the bedrock Perseverance has analyzed along its traverse, suggesting they were excavated from deeper crustal or mantle layers by the ancient impact that carved Jezero. Their presence on the surface means the crater’s geological record reaches far below what the rover can drill, offering a window into Mars’ deep interior chemistry. The fact that even some of these deep-sourced rocks show signs of aqueous interaction reinforces the idea that water was not a surface curiosity but a pervasive agent reshaping Jezero’s geology from top to bottom.
Iron Phosphates and the Habitability Question
Mineral evidence of water is necessary but not sufficient to argue for habitability. What elevates Jezero’s case is the discovery of Fe³⁺-bearing phosphate minerals embedded in a carbonate-rich matrix at an outcrop the team nicknamed “Onahu.” Published in Nature Communications, the finding relied on integrated rover analyses using Perseverance’s cameras, spectrometers, and X-ray diffraction instrument. Phosphorus is one of the six essential elements for life as scientists understand it, and finding it locked into minerals that formed in an aqueous, carbonate-buffered setting means Jezero once had both the energy sources and the chemical building blocks that microbial ecosystems require on Earth. The oxidized iron in these phosphates also hints at redox gradients that could have powered primitive metabolisms.
The carbonate matrix itself carries additional weight. NASA’s Jet Propulsion Laboratory has confirmed that carbonate-bearing rocks were sampled in Jezero, and carbonates on Earth are well known for preserving biosignatures, trapping organic molecules and microbial textures within their crystal lattices. If returned to Earth laboratories, these samples could be tested for isotopic fractionation patterns that distinguish biological from purely chemical processes, as well as for microscopic textures that reveal whether microbial mats once colonized the lakebed. The co-occurrence of kaolinite-rich rocks (indicating acidic rainfall), carbonated olivine (indicating CO₂-charged water), and iron phosphates (indicating bioavailable nutrients) within the same crater builds a layered argument. Jezero did not just have water, it had the kind of chemically active, nutrient-rich water that life exploits.
Crater Rim Exploration Adds New Context
Perseverance reached the Jezero crater rim on December 12, 2024, entering a new phase of its mission that targets rocks predating the lake itself. According to mission updates from rim investigations, the rover has been studying a diverse suite of lithologies exposed in the higher-standing terrain, including finely layered rocks that may record ancient airfall deposits and more massive units that could represent older volcanic or impact-related materials. These outcrops provide a stratigraphic backdrop for the minerals observed on the crater floor, helping scientists determine whether the water signatures are tied to a single lake episode or to multiple wet periods separated by drier intervals.
The rim campaign also offers a vantage point on Jezero’s broader landscape, allowing the science team to trace channels, deltas, and erosional features that once funneled water into the basin. By combining orbital mapping with in situ measurements, Perseverance can link specific mineral signatures to particular landforms, such as ancient shorelines or groundwater upwelling zones. This contextual information is crucial for interpreting the kaolinite-bearing float rocks and carbonate-rich units: if they can be tied to distinct layers or geomorphic settings, researchers can reconstruct how rainfall, surface runoff, and subsurface flow interacted through time to transform Jezero from a fresh impact scar into a habitable lake environment.
Sample Caching and the Path to Mars Sample Return
All of these discoveries gain significance because Perseverance is not just a field geologist, it is also a sample courier for future missions. The rover is systematically drilling and caching cores from key outcrops, guided by a science strategy developed by NASA mission planners and international partners. Each core, sealed in a metal tube, represents a carefully chosen snapshot of Jezero’s history: kaolinite-bearing float, carbonated igneous rock, fine-grained deltaic sediments, and the iron phosphate–bearing carbonates that may be especially promising for biosignature searches. The goal is to assemble a collection that spans different environments and alteration styles, maximizing the scientific return when these samples eventually reach Earth.
The current catalog of cached material, summarized in Perseverance’s evolving rock sample list, reflects that diversity. Some cores come from minimally altered igneous rocks that can anchor Mars’ volcanic and geochronological record, while others capture the heavily altered, water-processed units that speak directly to climate and habitability. Future Mars Sample Return missions, still in the planning stages, aim to retrieve a subset of these tubes and deliver them to terrestrial laboratories, where instruments far more sensitive than any rover payload can probe their chemistry, mineralogy, and potential biosignatures. In that sense, Perseverance’s findings about Jezero’s tropical-like past are not the final word but a roadmap, pointing to the specific pieces of Martian crust that may one day reveal whether life ever took hold on the Red Planet.
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*This article was researched with the help of AI, with human editors creating the final content.
