The announcement came framed with cautionary notes. Organics can have both a biological or non-biological origin, a fact NASA scientists emphasized. Mars rocks have fooled scientists before.

But they’re pumped about this vein-filled rock that they’ve dubbed “Cheyava Falls.” NASA said the rock was sampled July 21 on the edge of an ancient, wide river valley carved by water rushing long ago into Jezero Crater, before Mars lost most of its atmosphere and surface water and became a cold, parched world with dust storms and no sign of anything alive.

“We cannot say right now that we have discovered life on Mars,” said Katie Stack Morgan, the deputy project scientist. “But what we are saying is that we have a potential biosignature, which is a set of features that could have a biological origin but do need further study and more data.”

The reddish rock is covered with white patches known as “leopard spots.” These spots are produced by chemical reactions that on Earth are often associated with biological activity, Stack Morgan said.

“This is the kind of feature if found on Earth, life would probably be involved with it,” she said. “At the same time, these are chemical reactions that don’t require life.”

The rover has been traversing an ancient river delta in Jezero Crater, and pocketing samples of rock and soil as part of the ambitious but troubled Mars Sample Return mission. Cheyava Falls is an arrowhead-shaped rock that measures 3.2 feet by 2 feet, and is named after a waterfall in the Grand Canyon, NASA said.

The rover took a sample of the rock, the 22nd sample obtained so far. The general plan has been to send another spacecraft to the surface of Mars to be met by Perseverance for the sample transfer. Then the new lander will launch the material into orbit, where it will be transferred to yet another spacecraft — one provided by the European Space Agency — for the journey back to Earth.

But fears of cost overruns and delays have called into question whether NASA and its European partners can finish the job. In 2020, a review board estimated that Mars Sample Return would cost $3.8 billion to $4.4 billion. A review last year jacked that estimate to $8.4 billion to $10.9 billion, with samples not getting back to laboratories on Earth until 2040.

NASA officials said that wasn’t acceptable, and earlier this year put the mission on a bare-bones budget. They also asked the NASA Jet Propulsion Laboratory as well as outside contractors to propose new mission architectures that could bring down the cost and operational risk.

The rover does not have the kind of advanced technology necessary to tell if the leopard spots and organic molecules are biological or non-biological in origin, said Andrew Steele, an astrobiologist at the Carnegie Institution for Science who is part of the Perseverance scientific team.

But the rock’s environment, the presence of organics and the surface features are all compelling and make Cheyava Falls the most important sample obtained so far, he said.

“It just ticks all the boxes,” Steele said. “It’s very interesting chemistry with the iron and phosphate concentrations. It shows aqueous activity. It’s a great place for habitability.”

He is eager to see the new rock up close, back here on Earth.