A Mars rock sample collected last summer shows chemical fingerprints that might be traces of past microbe activity, though non-biological explanations are still possible, according to NASA.

The Perseverance rover found the rock in July 2024. The drilled sample, nicknamed Sapphire Canyon, is now the strongest clue scientists have that life once existed on ancient Mars, according to the U.S. space agency.

NASA held a news conference Wednesday to announce that the rover's findings have since passed peer review in the journal Nature, a key step in the scientific process to ensure the evidence is solid. Associate administrator Nicky Fox emphasized that the sample does not contain life itself but a fossilized remnant that suggests life had possibly been there.

"It's kind of the equivalent of seeing … leftovers from a meal, and maybe that meal has been excreted by a microbe," she said.

But whether this possible sign of life will ever be confirmed remains to be seen. Right now the sample is still on Mars, and it's unclear whether a NASA mission will ever bring it back to Earth for further analysis, crucial for getting to the point of certainty. In January, before President Donald Trump took office, NASA officials said they were working on two potential new approaches for Mars Sample Return that could cut costs. The decision for how to proceed would ultimately fall on the Trump administration, whose budget request calls for cancellation of this mission.

Acting NASA Administrator Sean Duffy, who Trump tapped to lead the agency two months ago, seemed disconcerted by the series of questions from reporters focusing on the mission and its funding rather than the research, which was announced last year.

"We got some of the brightest people at NASA with us," Duffy said during the event. "I was hoping your questions were going to be more on this exciting news that we have today."

The sample, taken from a site called Cheyava Falls, is one of 27 rock cores the rover has collected since landing on the Red Planet in February 2021.
Credit: NASA / JPL-Caltech

The sample, taken from a rock called Cheyava Falls, is one of 27 rock cores the rover has collected in tubes since landing on the Red Planet in February 2021. The Martian location where it was found was in Neretva Vallis, home to a bygone river that once emptied water into Jezero Crater, the region Perseverance has been exploring.

The rock is a reddish, clay-rich mudstone, with speckles and leopard spots that hint at chemical reactions similar to those that some microbes use for energy here on Earth. It contains organic carbon, sulfur, phosphorus, and iron-rich minerals that could have supported tiny life forms billions of years ago. Though these minerals can also form without living things, the local conditions make a non-biological explanation seem less likely.

"When we see features like this in sediment on Earth, minerals are often the byproduct of microbial metabolisms that are consuming organic matter and making these minerals as a result of those reactions," said Joel Hurowitz, lead author of the Nature paper. "But there are non-biological ways to make these features that we cannot completely rule out."

For example, an alternate way to make an iron-sulfide mineral known as greigite, detected in the sample, could be to heat the rock, said Hurowitz, a planetary scientist at Stony Brook University — essentially cooking those ingredients to create a new mineral phase.

Perseverance scientists say they've exhausted what they can learn about the sample with the car-sized rover's instruments. Back home, researchers could better inspect the material. Advanced tools could search for complex organic molecules, DNA, cell structures, and more.

Without the sample in hand, scientists will continue to pore over the rover's data by testing surrogate ingredients in laboratories, especially to see if they can create similar results in non-biological ways.

Mars Sample Return has been in limbo since a review found it would cost upward of $11 billion and take nearly two decades to achieve. NASA engaged the greater aerospace industry for input on how to wrangle in spending and development last year. Several companies suggested a variety of ideas, which Mashable reported, including repurposing Artemis moon landers and rethinking the last leg of the journey.

The mission is not off the table, said the acting administrator, who is also the U.S. transportation secretary, and the agency will continue to explore cost-saving options to make it feasible.

"If we don't have the resources for the right missions, or the right people, I will go to the president, I'll go to the Congress, I'll ask for more money," he said. "I feel pretty confident that with the money that we've been given in the president's budget, we can accomplish our mission."