NASA’s Perseverance rover, the first mission to collect and cache Martian rock and regolith
NASA/JPL-Caltech
On Mars, it’s the little things that hint at past life. In 2025, tiny details in rocks across the Martian surface have revealed some of the most exciting clues yet that there may once have been microbial life there.
These come from analysis of samples collected by NASA’s Perseverance rover, which began to provide evidence of life last year: Perseverance came across rocks with tiny splotches, each just millimetres wide with a ring of dark material around it. These splotches, dubbed “leopard spots”, are similar to features we see on Earth associated with fossils of microbes.
This year, Joel Hurowitz at Stony Brook University in New York state and his colleagues did more detailed analyses on the leopard spots, finding forms of iron and sulphur that often come from chemical reactions involving microbes. “I find it much more promising [an indication of life] than anything I’ve seen in the last 20 years,” says Hanna Sizemore at the Planetary Science Institute in Arizona.
Past findings that hinted at life on Mars included unexpected variation in the planet’s methane levels, along with fossil-like structures in Martian meteorites. “I am more enthusiastic about these findings than any of those,” says Sizemore. “That was all at the wrong physical scale.” The leopard spots, on the other hand, are just about the right size to be caused by microbes, she says.
The same is true for the other potential biosignatures Perseverance found this year: tiny greenish nodules of minerals that, on Earth, tend to be linked with microbial life. “It was always obvious that life there isn’t obvious. It’s not herds of wildebeests sweeping majestically across the plain,” says Andrew Steele at Carnegie Science in Washington DC, who was part of the team that developed the science goals for Perseverance. “Whatever these signs are, they’re going to be subtle, and we need the best instruments available to us to look for them.”
The Perseverance rover captured an image of a rock with distinctive “leopard spots”
NASA/JPL-Caltech/MSSS
Perseverance does have a sophisticated suite of scientific instruments, but if we want to definitively determine whether these rocks have signs of past life, we have to bring the samples back to Earth to be examined in laboratories here. That was always the plan: Perseverance would cache samples, and a future mission would pick them up and bring them back.
“These samples represent the best chance that we have of a next step in the analysis of whether there is [or has been] life on Mars – we just have to bring them back,” says Steele.
Unfortunately, that prospect is looking less and less likely. The Mars Sample Return project is marked for cancellation in the Trump administration’s proposed NASA budget for 2026; if that budget is approved, there will be no plan to pick up the samples that Perseverance has so carefully collected.
Indeed, it is possible that we have found signs of life on Mars and might never know it. “We keep making so much progress, but our big picture of Martian habitability keeps not moving,” says Sizemore. “We’re right on the edge – we cannot dismiss it and we cannot prove it. It’s only missions on the ground that will change that.”
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