Scientists were cautiously optimistic about Perseverance’s discovery, though they indicated further research is needed before drawing definitive conclusions

Eli Wizevich

July 29, 2024 4:32 p.m.

NASA’s Perseverance Mars rover sampled an arrowhead-shaped rock last week that contained tantalizing hints to the presence of ancient microscopic life. Although the evidence is compelling so far, scientists in charge of the mission are quick to caution that further research, which might include bringing the sample back to laboratories on Earth, is needed to determine whether they have truly found life on Mars.

Perseverance came across the intriguing rock, nicknamed “Cheyava Falls,” on July 21 as it explored the northern edge of Neretva Vallis, a quarter-mile-wide river channel created billions of years ago when water flowed into the nearby Jezero Crater.

“Cheyava Falls is the most puzzling, complex and potentially important rock yet investigated by Perseverance,” Ken Farley, a geochemist at the California Institute of Technology and a researcher on the Perseverance mission, says in a statement from NASA.

The rock is just three feet by two feet in size, but packed within its limited area are three possible signs of ancient life.

First, Perseverance discovered long, white veins of calcium sulfate, a mineral likely deposited by flowing water, streaking across the rock’s reddish surface. Calcium sulfate’s presence bolsters the theory that Neretva Vallis and Jezero Crater were once abundant in water and therefore hospitable to life.

The rover also picked up on dozens of millimeter-sized white blobs on the rock, each surrounded by a black ring in a pattern reminiscent of leopard spots.

“These spots are a big surprise,” says David Flannery, an astrobiologist and member of the Perseverance science team from the Queensland University of Technology in Australia, in the statement. “On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface.”

Using PIXL, an X-ray instrument on the rover, NASA researchers found the black rings contain both iron and phosphate. These products are indicative of chemical reactions with hematite—one of the minerals that gives Mars its distinctive red color—that could have provided an energy source for microbial life.

“We should be cautiously enthused but pragmatically restrained,” Paul Byrne, a planetary geologist at Washington University in St. Louis who is not involved with the rover project, tells New Scientist’s Leah Crane. “For now, this is a sign of (probably) wet rocks undergoing chemical alteration.”

Finally, after scanning the rock, Perseverance found organic compounds using its SHERLOC instrument. Organic compounds are often signs of carbon-based life, but scientists caution they can sometimes form through non-biological processes.

“What we are saying is that we have a potential biosignature on Mars,” Kathryn Stack Morgan, a leading researcher on the mission, tells the New York Times’ Kenneth Chang.

Each of these signs is interesting on its own, but to find all three together on the same rock is unheard of—and it makes an especially strong case for life. Still, the researchers stress that the full story behind these signs of life is unknown, and they haven’t yet discovered fossilized organisms or other definitive pieces of evidence.

“On the one hand, we have our first compelling detection of organic material, distinctive colorful spots indicative of chemical reactions that microbial life could use as an energy source, and clear evidence that water—necessary for life—once passed through the rock,” Farley adds in the statement. “On the other hand, we have been unable to determine exactly how the rock formed and to what extent nearby rocks may have heated Cheyava Falls and contributed to these features.”

In one possible scenario for its formation, Cheyava Falls started off as mud, already rife with organic compounds, before these components were carried into Neretva Vallis by water and cemented into rock with time. Then, water oozed into the cracks of the solid rock, creating the calcium sulfate veins and enabling the chemical reactions that left the leopard spots.

But complicating this story is the presence of olivine, a mineral that forms from magma. Instead, the olivine in Cheyava Falls suggests another scenario in which the black and white splotches on the rock were produced by an abiotic chemical reaction that occurs at “uninhabitably high temperatures,” according to the statement.

While Perseverance’s discovery has made strides toward potentially finding ancient life on Mars, the rover’s capacity to answer these remaining questions is limited.

“We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable,” Farley says in the statement. “Scientifically, Perseverance has nothing more to give.”

Instead, scientists hope to study the rock close-up. A core taken from Cheyava Falls has been added to Perseverance’s collection of samples to bring back to labs on Earth. But until NASA hammers out the details, budget and timeline of its Mars sample return mission—which is controversial, expensive and still uncertain—mysteries will remain about life on the Red Planet.

Source: https://www.smithsonianmag.com/smart-news/mars-rover-finds-three-possible-signs-of-ancient-life-on-a-single-rock-180984783/?utm_source=smithsoniandaily&utm_medium=email&utm_campaign=editorial&spMailingID=50023925&spUserID=MTI1MzcyNjIxNjk1NAS2&spJobID=2743128771&spReportId=Mjc0MzEyODc3MQS2