An abandoned rock sample could prove life once existed on Mars. But will it ever reach Earth? - CNN

A leopard-spotted rock that could prove whether life ever existed beyond Earth is sitting in a tube on Mars.

NASA’s Perseverance rover grabbed up the sample, called Sapphire Canyon, from rocky outcrops on the edges of the Neretva Vallis, a valley sculpted by rivers that once flowed into an ancient lake in Jezero Crater more than 3 billion years ago. The rover landed at the dried lakebed in February 2021 for expressly this purpose, hunting for rocks created or modified by water in the past, which would have had the best chance of preserving evidence of life.

Members of the Perseverance science team have said the Sapphire Canyon sample, about the size of a chalk stick, is exactly the type of rock they hoped the rover would discover.

“This is the first time I think we’ve found something that qualifies as a ‘potential biosignature’” on Mars, said Adrian Broz, a member of Perseverance’s science team and a postdoctoral researcher in the Planetary Surface Processes Lab at Purdue University in Indiana. “It’s currently sealed inside of Perseverance rover’s chassis, and it sits there quietly and awaits return to Earth.”

But the sample might not make it to our planet, at least not anytime soon.

The Mars Sample Return program, a joint venture by NASA and the European Space Agency to ferry the promising cache back to Earth, attracted intense scrutiny for its high price tag and complex design. After sinking billions of dollars into the endeavor, NASA paused and began reassessing the program in 2024 before canceling it entirely — with no clear alternative in sight.

“While Perseverance’s samples remain safely stored on Mars, NASA is exploring a range of potential return options that could offer simpler and more affordable approaches than the original Mars Sample Return plan, including possible commercial or international contributions,” the agency said in a statement shared with CNN in July. NASA’s leaders still haven’t revealed a path forward.

And while the discovery of the Sapphire Canyon sample is building a strong case for the existence of ancient microbial life on Mars, there’s only so much scientists can learn from afar, said Dr. Briony Horgan, professor of Earth, atmospheric and planetary sciences at Purdue University.

The rover, which cost NASA about $2.4 billion to build and launch, doesn’t have the instrument suite to answer such lofty questions by itself on the red planet.

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“We can keep doing these studies and coming up with these hints, but we’re never going to know for sure until we get those samples back,” said Horgan, also a coinvestigator and planner on the Perseverance team. “These samples are our best current chance for really understanding is life abundant and common, or is Earth truly unique?”

Now, it’s possible one of NASA’s biggest competitors in the new space race will be the first to achieve Mars sample retrieval: China is looking to pick up its own souvenir from the red planet in 2031, and it has taken steps to ensure success by designing a mission that’s similar to one it pulled off two years ago. But the rocks returned by the country’s Tianwen-3 mission, expected to launch in 2028, could look very different — and perhaps offer different insights — from Perseverance’s samples, depending on how plans evolve.

Scientists consider Sapphire Canyon such a promising find because of its spotted appearance. On Earth, the tiny dots, called reaction fronts or reduction spots, form in soils and sediments due to the presence of microbial activity.

“When there’s organic matter that’s lodged in sediment or soil that’s buried and microbes start to digest some of that organic matter, they form these bleached halos and spots that are quite resemblant to the ones that Perseverance found in this ancient river valley,” said Broz, coauthor of a study about the rock sample published in September 2025.

Perseverance drilled the Sapphire Canyon sample from an arrowhead-shaped rock called Cheyava Falls in July 2024. The mudstones surrounding the rock were also covered in hundreds of thousands of promising reduction spots potentially made by ancient microscopic life.

Still, returning the samples to Earth is the only way to determine whether these distinctive features were formed by the presence of life, or abiotically — through chemical or geological processes that did not require life, Broz said.