NASA’s Perseverance rover, the first mission to collect and cache Martian rocks and regolith
NASA/JPL-Caltech
On Mars, it’s the little things that hint at a past life. In 2025, tiny details in rocks on the Martian surface revealed some of the most exciting clues yet that microbial life might have existed there.
These come from analysis of samples collected by NASA’s Perseverance rover, which began yielding evidence of life last year: Perseverance encountered rocks with tiny specks, each just a few millimeters wide, surrounded by a ring of dark matter. These spots, nicknamed “leopard spots,” are similar to features we see on Earth associated with microbe fossils.
This year, Joel Hurowitz of Stony Brook University in New York state and his colleagues performed more detailed analyzes on the leopard’s spots, finding forms of iron and sulfur that often come from chemical reactions involving microbes. “I find this much more promising [an indication of life] than anything I’ve seen in the last 20 years,” says Hanna Sizemore of the Planetary Science Institute in Arizona.
Previous discoveries hinting at life on Mars included unexpected variations in the planet’s methane levels, as well as fossil-like structures in Martian meteorites. “I’m more excited about these results than any of them,” Sizemore says. “All of this was not on the right physical scale.” Leopard spots, on the other hand, are about the right size to be caused by microbes, she says.
The same goes for other potential biosignatures found by Perseverance this year: tiny greenish nodules of minerals that, on Earth, tend to be linked to microbial life. “It’s always been obvious that life there is not obvious. It’s not herds of wildebeest sweeping majestically across the plain,” says Andrew Steele of Carnegie Science in Washington DC, who was part of the team that developed Perseverance’s science goals. “Whatever these signs are, they will be subtle and we need the best instruments at our disposal to look for them.”
Perseverance rover captured image of rock with distinctive ‘leopard spots’
NASA/JPL-Caltech/MSSS
Perseverance has a sophisticated suite of scientific instruments, but if we want to determine with certainty whether these rocks show signs of past life, we need to bring the samples back to Earth to examine them in laboratories. This was always the plan: Perseverance would cache samples, and a future mission would retrieve and bring them back.
“These samples represent the best chance we have to take the next step in analyzing whether there is [or has been] life on Mars – we just have to bring them back,” says Steele.
Unfortunately, this prospect seems less and less likely. The Mars Sample Return project is expected to be canceled in the Trump administration’s proposed 2026 NASA budget; if this budget is approved, there will be no plan to recover the samples that Perseverance has so carefully collected.
Indeed, it is possible that we have found signs of life on Mars and will never know it. “We continue to make a lot of progress, but our overall vision of Martian habitability is not moving,” Sizemore says. “We are at the limit – we cannot ignore it and we cannot prove it. Only missions on the ground can change this.”
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