The Perseverance Mars rover collected the "Sapphire Canyon" rock samples in July 2024 from what's thought to be an ancient lakebed, and its poppyseed and leopard-esque spots pointed to potential chemical reactions that piqued the interest of researchers.

If the features resulted from microbial activity that created minerals in the way they do on Earth -- well, that might point to life on Mars.

It's far too soon for scientists to say that definitively, but the findings, which were detailed in research published in the journal Nature, are alluring.

"We put it out to our scientific friends to pressure test it, to analyze it, and go, did we get this right? Do we think this is signs of ancient life on Mars?" NASA's Acting Administrator Sean Duffy said at a news conference.

"They said, 'Listen, we can't find another explanation.' So this very well could be the clearest sign of life that we've ever found on Mars."

"It's kind of the equivalent of seeing like leftover fossils, leftovers from a meal, and maybe that meal has been excreted by a microbe," Nicky Fox, administrator of NASA's Science Mission Directorate, told journalists.

When those kinds of mineral and textured features form in sediment on Earth, it's frequently the product of reactions from mud and organic matter, explained the study's lead author Joel Hurowitz -- a potential "biosignature," or sign of life.

Specifically, Perserverance's instruments identified the minerals vivianite and greigite. On Earth, vivianite is often found in sediments, peat bogs, and around decaying organic matter. Some forms of microbial life on Earth can produce greigite.

"But there are non-biological ways to make these features that we cannot completely rule out on the basis of the data that we collected," Hurowitz said.

Still, the findings are "exciting," he told journalists, explaining that researchers would need to analyze the sample in person to better understand if microbial activity had created the "fantastic textures" and colors including blue and green.

- 'Are we alone in universe?' -

That's no small feat, particularly in light of President Donald Trump administration's plans to cancel the Mars Sample Return program -- a robotic mission planned for the 2030s to bring Perseverance's samples back to Earth.

Asked by journalists if that was still the plan, Duffy was non-committal, hinting the samples might be brought back by a future crewed mission instead.

"We care about resources, we care about the timeframe, we believe there's a better way to do this, a faster way to get these samples back. And so that is the analysis that we've gone through. Can we do it faster? Can we do it cheaper? And we think we can," he said.

There are several rovers ambling across Mars -- Perseverance has been there since 2021 -- seeking signs of life that could have existed millions to billions of years ago, when the planet was thought to have been more habitable.

Evidence that ancient rivers and lakes carved into the planet's surface would indicate that water once flowed there.

And the latest discovery, said Fox, brought researchers "one step closer" to answering the burning question: "Are we truly alone in the universe?"