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NASA's Perseverance rover has identified rock samples in an ancient Martian riverbed that contain features potentially linked to microscopic life from billions of years ago, researchers announced Wednesday.
The discovery, detailed in the journal Nature, represents what scientists describe as their most promising evidence yet in the search for signs of past life on Mars. However, researchers emphasized that definitive conclusions require extensive laboratory analysis on Earth.
The sample was collected last summer from reddish, clay-rich mudstones within Neretva Vallis, a dried river channel that once flowed into Jezero Crater. The rock formation, part of what scientists call the Bright Angel formation, contained organic carbon alongside microscopic features enriched with iron phosphate and iron sulfide.
The tiny formations, which researchers nicknamed "poppy seeds" and "leopard spots," mirror chemical compounds produced on Earth when microorganisms break down organic matter. In terrestrial environments, similar interactions occur between microorganisms and minerals in Antarctic lakes.
"It would be amazing to be able to demonstrate conclusively that these features were formed by something that was alive on another planet billions of years ago, right?" said Joel Hurowitz of Stony Brook University, the study's lead researcher. "But even if that's not the case, it's a valuable lesson in all of the ways that nature can conspire to fool us."
External scientists not involved in the research cautioned against drawing premature conclusions. SETI Institute's Janice Bishop and the University of Massachusetts Amherst's Mario Parente noted that non-biological processes could produce identical results.
"That's part of the reason why we can't go so far as to say, 'A-ha, this is proof positive of life,'" Hurowitz told The Associated Press. "All we can say is one of the possible explanations is microbial life, but there could be other ways to make this set of features that we see."
The sample marks the 25th collected by Perseverance since its 2021 arrival on Mars. The rover now holds 30 samples, with plans to gather six more before completing its collection mission.
NASA's original timeline called for returning these samples to Earth by the early 2030s, but mounting costs reaching $11 billion have pushed that goal into the 2040s. The space agency is currently exploring cheaper, faster alternatives for the sample return mission.
Ten backup sample tubes were deposited on Mars' surface several years ago as insurance against potential rover failures. Until samples reach Earth-based laboratories, scientists must rely on terrestrial analogues and remote analysis to evaluate the possibility of ancient Martian life.
"There is no evidence of microbes on Mars today, but if any had been present on ancient Mars, they too might have reduced sulfate minerals to form sulfides in such a lake at Jezero Crater," Bishop and Parente wrote in an accompanying editorial.
The findings add to growing scientific interest in Mars' potential to have harbored life during its early history, when the planet maintained warmer temperatures and liquid water on its surface.
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