NASA’s Perseverance rover has bagged its first hint of ancient microbes on Mars.
“We’re not able to say that this is a sign of life,” says Perseverance deputy project scientist Katie Stack Morgan of NASA’s Jet Propulsion Lab in Pasadena, Calif. “But this is the most compelling sample we’ve found yet.”
The rover drilled up the sample on July 21 from a reddish rock, dubbed Cheyava Falls after a feature at the Grand Canyon. It is the first piece of Mars that Perseverance has examined that contains organic molecules, the building blocks of life, project scientist Ken Farley of Caltech reported July 25 at the 10th International Conference on Mars in Pasadena.
This isn’t the first sign of organics on Mars — the Curiosity rover detected organic molecules in a region called Gale Crater in 2014 (SN: 12/16/14). But scientists have struggled to identify organics since Perseverance landed in an ancient dried-up lake called Jezero Crater in 2021, says Stack Morgan (SN: 2/17/21).
Adding to the excitement, the reddish rock is speckled with little white spots with black rims. “They look like a tricolored leopard spot,” Stack Morgan says.
Perseverance examined the spots with instruments that can identify their chemical contents and found that the rims contain iron phosphate molecules. On Earth, rings with similar texture and chemistry are associated with ancient microbial life. The chemical reactions that create the rings can be an energy source for microbes.
“They don’t require life, of course, and that’s an important caveat,” Stack Morgan says. “But based on our experience with similar things on Earth, there is a possibility that life could have been involved, and these could have a biological origin.”
The rock has other confusing features that muddy the picture of how it formed, Stack Morgan says. It is shot through with white veins of calcium sulfate. These veins are filled with millimeter-sized crystals of olivine, a mineral that forms from magma. The inclusion of both the spots and these volcanic features in the same rock is “a little bit mysterious,” Stack Morgan says, as they point to different origins. Figuring out how the rock formed could help tell how likely it is to have had the right conditions and temperatures to host biology.
Planetary scientist Paul Byrne thinks we should be circumspect about the finding.
“Could this truly be a biosignature? Yes. And if it is, then it really is the kind of society-altering discovery that the discovery of truly extraterrestrial life would be,” says Byrne, of Washington University in St. Louis. But it’s also possible that the spots came from something other than life, “in which case all this is is an interesting example of water-rock chemistry.”
The only way to find out for sure is to bring the rock home. A big part of Perseverance’s mission is to collect samples from interesting rocks for a future spacecraft to return to Earth, where they can be studied in more sophisticated laboratories than a rover can carry on its back. Perseverance has thrown everything it has at this rock already, Stack Morgan says.
But funding uncertainty has recently put the program, known as Mars Sample Return, on hold (SN: 5/8/24).
“With this sample, the rationale for MSR is strengthened even more, and should I hope motivate NASA to commit to pulling off this project sooner rather than later,” Byrne says.
Stack Morgan says the rover team is carrying on despite the budget uncertainty.
“We have a mission to carry out, and a job to do: collecting compelling samples,” Stack Morgan says. “It can only be our hope that the samples that we collect are compelling enough to justify the cost of Mars Sample Return. I think with this exciting sample, that really hits that home.”
