Thousands of strange white rocks found on Mars. Will they ever be brought to Earth?

NASA's Perseverance Mars rover used its dual-camera Mastcam-Z imager to capture this image of "Santa Cruz," a hill within Jezero Crater, on April 29, 2021.
NASA's Perseverance Mars rover used its dual-camera Mastcam-Z imager to capture this image of "Santa Cruz," a hill within Jezero Crater, on April 29, 2021. (Image credit: NASA/JPL-Caltech/ASU/MSSS)

Mars' rusty red surface may have given it its famous "Red Planet" status, but it would also appear that thousands of white rocks are strangely littered on the Martian ground. NASA's Perseverance rover, a robotic geologist that has been exploring the Jezero Crater since early 2021, puzzled scientists when it delivered images of over 4,000 light-toned, pebble-sized rocks scattered all over the crater floor.

"These are very unusual rocks and we're trying to figure out what's been going on," Candice Bedford, a planetary scientist at Purdue University in Indiana and a member of the Mars 2020 science team, said at the Lunar and Planetary Science Conference (LSPC) last month.

The announcement comes as NASA wraps up an architectural review of returning Martian rocks to Earth as part of the agency's ambitious Mars Sample Return (MSR) program.

Related: NASA's Perseverance rover captures 360-degree view of Mars' Jezero Crater (video)

The imaged white rocks are what scientists refer to as "floats," meaning they have been removed and transported from their original habitats; some are smooth with pits while others appear to be an amalgamation of multiple layers. Initial analyses, conducted with Perseverance's onboard instruments, revealed the rocks are dehydrated — not only in water content, but also in other minerals including iron, magnesium, calcium and sodium. "These are pretty depleted in a lot of things," Bedford said.

The team is particularly interested in the origins of these unusual rocks as their sources can reveal clues about the Red Planet's past, including precisely when water would've flooded the Jezero crater, which we see as an arid stretch of land today. Despite spotting more than 4,000 such rocks, Perseverance hasn't managed to see even a hint of what's known as an "outcrop" related to the rocks, which is essentially a bedrock of similar properties that'd jut out of the Martian surface. 

The rocks' dehydrated nature suggests they were heated and metamorphosed by either lava flows or asteroid impacts elsewhere on Mars and later dumped onto the crater floor, said Bedford. Whatever the specific process may have been, she and her team suspect it would have occurred relatively recently in terms of Jezero Crater's geologic history.

The Perseverance rover, which has driven more than 15 miles (24.8 kilometers) since its arrival on Mars, celebrated 1,000 days of science last December, which also marked the official completion of the mission it was originally designed to do. It has now filled 26 of its 43 Mars rock sample tubes, mission team members shared at LPSC. "Each sample has innumerable grains that we could potentially study for forever, essentially," said Benjamin Weiss, a professor of planetary sciences at the Massachusetts Institute of Technology and a member of the Mars 2020 team.

As part of a bonus mission that kicked off this spring, Bedford said Perseverance began inching its way toward the Jezero Crater rim, and its long-distance camera has already imaged more light-toned rocks scattered in that area as well.

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All of these puzzling rocks, however, are not the only reason why scientists are eager to get Perseverance to the crater rim and possibly beyond. There, they believe a unique geology exists, one that hasn't yet been encountered within the crater floor. That includes pre-Jezero rocks that may have records of the formation of Mars' crust and early climate. It may even hold evidence of biosignatures.

Scientists are currently tagging a variety of interesting sampling locations while mapping the rim itself in more detail, said Lisa Mayhew, a research associate at the University of Colorado, Boulder. Of much interest to scientists is a terrain adjacent to Jezero crater called Nili Planum, whose rocks they think would have formed in warm conditions during a time when life most likely evolved — if it ever existed on the now-barren world, that is. Sampling such rocks "would provide huge added scientific value to the cache that's already existing on Perseverance," said Mayhew.

That scientific value, however, can only be fully realized after those rocks are returned to Earth

Scientists need to time-date them using equipment on Earth, without which they wouldn't have a precise timeline for when the Red Planet was habitable and when it became parched. "It doesn't overstate to say it will revolutionize our understanding of Mars," said Weiss.

Questions remain about the MSR program, which NASA is spearheading, including when and how the agency plans to return collected samples to Earth. Last October, NASA commissioned a response team (MIRT) to evaluate alternative approaches to MSR after an independent review board (IRB) found the current architecture would lead to overruns in cost and schedule.

"Much of the work is already complete," said Meenakshi Wadhwa, a planetary scientist at Arizona State University and MSR's principal scientist. The MIRT's recommendation report for a new approach was expected by the end of March, followed by a revised plan and budget by NASA sometime in April, she said.

The agency's fiscal year 2025 budget proposal, made public March 11, allocated $2.7 billion for planetary science but the funding for MSR remained "TBD." NASA's budget this year and next will be announced in April after the MIRT review is completed, NASA Administrator Bill Nelson told reporters at the time.

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Sharmila Kuthunur
Space.com contributor

Sharmila Kuthunur is a Seattle-based science journalist covering astronomy, astrophysics and space exploration. Follow her on X @skuthunur.