By analyzing high-resolution geochemical data from the rover, scientists have identified two dozen types of minerals, the building blocks of rocks, that help reveal a dynamic history of volcanic rocks that were altered during interactions with liquid water on Mars. The findings, published in the Journal of Geophysical Research: Planets, provide important clues for the search for ancient life and help guide Perseverance's ongoing sampling campaign.
The study was led by Rice University graduate student Eleanor Moreland and employed the Mineral Identification by Stoichiometry (MIST) algorithm - a tool developed at Rice - to interpret data from Perseverance's Planetary Instrument for X-ray Lithochemistry (PIXL). PIXL bombards Martian rocks with X-rays to reveal their chemical composition, offering the most detailed geochemical measurements ever collected on another planet, according to the study.
"The minerals we find in Jezero using MIST support multiple, temporally distinct episodes of fluid alteration," Moreland said, "which indicates there were several times in Mars' history when these particular volcanic rocks interacted with liquid water and therefore more than one time when this location hosted environments potentially suitable for life."
Minerals form under specific environmental conditions of temperature, pH and the chemical makeup of fluids, making them reliable storytellers of planetary history. In Jezero, the 24 mineral species reveal the volcanic nature of Mars' surface and its interactions with water over time. The water chemically weathers the rocks and creates salts or clay minerals, and the specific minerals that form depend on environmental conditions. The identified minerals in Jezero reveal three types of fluid interactions, each with different implications for habitability.
The first suite of minerals - including greenalite, hisingerite and ferroaluminoceladonite - indicate localized high-temperature acidic fluids that were only found in rocks on the crater floor, which are interpreted as some of the oldest rocks included in this study. The water involved in this episode is considered the least habitable for life, since research on Earth has shown high temperatures and low pH can damage biological structures.
"These hot, acidic conditions would be the most challenging for life," said co-author Kirsten Siebach, assistant professor of Earth, environmental and planetary sciences at Rice. "But on Earth, life can persist even in extreme environments like the acidic pools of water at Yellowstone, so it doesn't rule out habitability."
The second suite of minerals reflects moderate, neutral fluids that support more favorable conditions for life and were present over a larger area. Minerals like minnesotaite and clinoptilolite formed at lower temperatures and neutral pH with minnesotaite detected in both the crater floor and the upper fan region, while clinoptilolite was restricted to the crater floor.
Finally, the third category represents low-temperature, alkaline fluids and is considered quite habitable from our modern Earth perspective. Sepiolite, a common alteration mineral on Earth, formed under moderate temperatures and alkaline conditions and was found widely distributed across all units the rover has explored. The presence of sepiolite in all of these units reveals a widespread episode of liquid water creating habitable conditions in Jezero crater and infilling sediments.
"These minerals tell us that Jezero experienced a shift from harsher, hot, acidic fluids to more neutral and alkaline ones over time - conditions we think of as increasingly supportive of life," Moreland said.
Because Mars samples can't be prepared or scanned as precisely as Earth samples, the team developed an uncertainty propagation model to strengthen its results. Using a statistical approach, MIST repeatedly tested mineral identifications considering the potential errors, similar to how meteorologists forecast hurricane tracks by running many models.
"Our error analysis lets us assign confidence levels to every mineral match," Moreland said. "MIST not only informs Mars 2020 science and decision-making, but it is also creating a mineralogical archive of Jezero Crater that will be invaluable if samples are returned to Earth."
The results confirm that Jezero - once home to an ancient lake - experienced a complex and dynamic aqueous history. Each new mineral discovery not only brings scientists closer to answering whether Mars ever supported life but also sharpens Perseverance's strategy for which samples to collect and return.
This publication provides a thorough compilation of minerals identified using the MIST model for the first three years of Perseverance's mission. While it does not include the specific sampling site presented in the press release about detection of a potential biosignature, this work provides context for how the habitable conditions observed for that sample, Sapphire Canyon, were present more broadly in Jezero. This context-setting information is key to any interpretation of the potential biosignatures that were identified.
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