After a year of intensive study and independent review, the rock sample that NASA’s Perseverance rover drilled out of an ancient mudstone on Mars last summer has lived up to the eye-watering prospect that it holds possible chemical evidence of past microbial life.
“This finding . . . is the closest we’ve actually come to discovering ancient life on Mars,” Nicky Fox, NASA associate administrator for science, told reporters Sept. 10. “[From] everything we know about life on Earth, this is the kind of signature we would see that was made by something biological. In this case, it’s kind of the equivalent of seeing leftovers from a meal, and maybe that meal had been excreted by a microbe. That’s what we’re seeing in this sample.”
At the moment, the U.S. has no plan to retrieve the sample and fly it—and as many as 29 others collected during the ongoing Perseverance mission—to Earth for analysis. “We’re going to look at our budget . . . and look at our timing [to see] how we spend money better, what technology we have to get samples back more quickly . . . and what is the best way to do it,” NASA acting Administrator Sean Duffy said at the Sept. 10 press conference. “That analysis is happening now.”
The prized sample—the 25th in a still-growing collection—was drilled on July 21, 2024, from a rock in Neretva Vallis, an ancient 1,300-ft.-wide river valley that was carved by water rushing into Jezero Crater long ago. The rover landed inside the crater on Feb. 18, 2021, to search for locations that could have supported and preserved evidence of past microbial life and to cache samples to send to Earth.
Sample 25 is the only one that has been confirmed to contain organic materials. The reddish rock has white-toned spots encircled by black rings. Chemically, the light-tone and reddish areas of the rock are the same, suggesting that the features, nicknamed leopard spots, are areas that have been bleached out by another process.
On Earth, similar spotting typically occurs during chemical reactions involving hematite, which can release iron and phosphate to form black rings. These types of reactions can be an energy source for microbes.
In the year since the sample was cached, scientists worked to understand better the environment in which the rocks formed and what chemical reactions could have occurred to create the potential biosignatures. For example, the team determined there was not widespread heating in the region, which could have provided a geologic explanation for the spots.
Ultimately, the determination of whether the rock contains evidence of extraterrestrial life cannot be answered until the sample is brought to Earth for analysis. “We basically threw the entire rover science payload at this rock,” said Perseverance Project Scientist Katie Stack Morgan, with NASA’s Jet Propulsion Laboratory in California. “We’re pretty close to the limits of what the rover can do on the surface in terms of making progress on that particular question. That was by design, since the payload of the Mars Perseverance rover was selected with a sample return in mind.”
Citing costs and schedule concerns, NASA in 2023 paused its overbudget, multispacecraft Mars Sample Return (MSR) campaign, which had been in development with the European Space Agency since 2009. With cost estimates more than doubling the program’s planned $4-5 billion budget, NASA vetted alternatives in 2024 and left to the incoming Trump administration and Congress the decision on how to proceed.
In its spending plan for fiscal 2026, which begins Oct. 1, the White House proposes to end the MSR program formally as part of a nearly 50% cut in NASA science programs and an overall 24% reduction in the agency’s budget. Legislation passed by the House and Senate Appropriations Committees maintain NASA’s annual funding close to its current $25 billion level. The House bill includes $300 million for MSR, the top priority of the U.S. Planetary Science Decadal Survey. The Senate bill does not specifically mention MSR. A 2026 budget has not been passed.
In a related initiative, NASA is proceeding with plans to procure a new Mars telecommunications orbiter to buttress the aging fleet of spacecraft currently supporting the rovers and other Mars science missions. Among the bidders: Rocket Lab, which pitched the communications segment of a MSR mission concept presented to NASA in 2024. Rocket Lab estimated the price of its MSR program at $4 billion.
