Strange nodules of unusual minerals found on speckled rocks on Mars have offered more tantalizing clues that ancient life may have once thrived on the now-dead planet, NASA says.

NASA’s Perseverance rover found one such arrow-shaped rock, nicknamed Cheyava Falls, in 2024 along the northern bank of Neretva Vallis, the dried-up remnants of an ancient river that once rushed into Mars’ Jezero crater. An initial analysis of the rock, which appeared in a lake bed formation known as Bright Angel, revealed it was crammed with organic compounds, had evidence that water once flowed through it, and contained flecks of leopard-like spots from chemical reactions that ancient microbes could have used for energy.

These features may result from non-biological processes occurring over millions of years. But now, in a new study published in the journal Nature, NASA scientists have announced intriguing details about additional rock samples found at two nearby sites — and they say these clues bolster the case for past life on Mars. “After a year of review, they have come back and they said, listen, we can’t find another explanation,” Acting NASA Administrator Sean Duffy, said during a news briefing following the announcement. “So this very well could be the clearest sign of life that we’ve ever found on Mars, which is incredibly exciting.”

Since arriving on Mars in 2021, Perseverance has been trundling across the 30-mile-wide Jezero crater, collecting dozens of rock samples for eventual return to Earth. Upon finding the leopard-spotted rock, scans by the rover’s Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument showed that the specimen contained carbon-based molecules, alongside bands of reddish hematite that featured spots of iron and phosphate. “When the rover entered Bright Angel and started measuring the compositions of the local rocks, the team was immediately struck by how different they were from what we had seen before,” study co-author Michael Tice, a geobiologist and astrobiologist at Texas A&M University, said in a statement. “They showed evidence of chemical cycling that organisms on Earth can take advantage of to produce energy. And when we looked even closer, we saw things that are easy to explain with early Martian life but very difficult to explain with only geological processes.”