An arrowhead-shaped rock on Mars sporting features that may hint at ancient microbial activity on the Red Planet has left scientists puzzled.
NASA announced in July of last year that the rock, found in Mars’ Jezero Crater by the agency’s Perseverance rover, held some of the best evidence yet that ancient microbial life may have existed on the Red Planet billions of years ago, when it was significantly wetter than it is today. Earlier this week, scientists involved with the discovery presented their findings publicly for the first time this week at the Lunar and Planetary Science Conference in Texas, detailing the rock’s chemical signatures and structures that continue to offer tantalizing hints of ancient Martian microbial life.
The fine-grained mudstone named Cheyava Falls, after the highest waterfall in Arizona’s Grand Canyon, sits at the edge of an ancient river valley known as Neretva Vallis, which runs along the inner wall of the crater. The rock features spots of black, blue, or greenish hues, which the researchers have nicknamed “poppy seeds.” Alongside these are dozens of dark-rimmed, millimeter-size splotches dubbed “leopard spots.” Perseverance’s instruments have revealed that several rocks hosting these two features are rich in iron, but that they vary in their oxidation states and redness — a telltale sign of activity by organic matter, which may have bleached the rocks of their red color.
“On Earth, reactions like these are commonly associated with microbially-driven organic matter respiration,” Joel Hurowitz, the deputy principal investigator of the PIXL instrument located at the end of Perseverance’s robotic arm, said at the conference.
Back in July, the discovery team had also noted the presence of calcium sulfate veins running through the rock, suggesting that water may have once flowed through it. While this and other features could point to non-biological processes, such as exposure to high temperatures from a volcanic event, ongoing analysis suggests the rock was never subjected to such heat or exposed to heat-related processes that would have caused it to recrystallize. “Everything seems to be consistent with low-temperature processes,” Hurowitz said.
Scientists suspect the Neretva Vallis channel was carved out eons ago, by water gushing into the crater. One theory is that mud loaded with organic compounds was deposited into the valley, later cementing into the Cheyava Falls rock. Alternatively, a second water episode could have seeped into the rock after it had already formed, creating the features observed. “The rocks that we investigated appear to fill the Neretva Vallis channel,” Hurowitz said.
There are no life-detection instruments onboard Perseverance, as its mission is to collect samples of scientific interest that will be returned to Earth for further scrutiny.
“As a community, we should feel compelled to do a whole lot of laboratory, field and modeling studies to try to investigate features like this in more detail,” Hurowitz said. “And ultimately bring these samples back home so that we can reach a conclusion with regard to whether they were or were not formed by life.”
However, details of the troubled Mars Sample Return effort remain uncertain after costs that ballooned to $11 billion led NASA to overhaul its approach and seek new ideas from its research centers, private industry and academia.
Former NASA administrator Bill Nelson announced earlier this year that the agency is leaving two options for the Trump administration to return to Earth 30 cigar-sized tubes containing bits of Mars that Perseverance has been collecting since 2021, including the Cheyava Falls sample. The two approaches differ in the way they would put hardware down on Mars, but either would require Congress to allocate $300 million to the mission for it to start launch proceedings by 2030 and return the samples between 2035 and 2039.
Scientists are eager to analyze the Cheyava Falls sample, as it could help answer one of humanity’s most profound questions: Are we alone in the universe?
“The discovery of life beyond Earth is so profound, so paradigm-shifting, you have to get it right,” Amy Williams, an astrobiologist at the University of Florida who’s on the Perseverance science team, had told Space.com shortly after the discovery. “Once you cross that line, you can’t come back.”