Mars' leopard print may be the most powerful evidence of life

NASA 's Perseverance rover has discovered possible signs of ancient life, which scientists say is one of the strongest evidences yet of life on Mars.

The "leopard pattern" on Martian rocks may be evidence of microbial involvement in chemical reactions. Image credit: NASA/JPL-Caltech/MSSS

"Leopard prints" on a rock studied by the Mars rover last year may be the remains of microbial activity on Mars, researchers said March 12 at the Lunar and Planetary Science Conference in Texas.

But while the patterns look a lot like spots produced by microbes on Earth, the researchers say they could also have formed without the involvement of living organisms, although they don't fully understand the Martian chemical and physical processes that might be at work.

For now, the discovery still ranks 1 on a 1 to 7 scale for assessing extraterrestrial life -- 1 being the detection of an interesting signal and 7 being absolute confirmation. Jim Green, NASA's former chief scientist who developed the scale, said he hopes researchers can get additional confirmation to move it up a notch. To do that, the "leopard print" rock will need to be brought back to Earth for analysis. Perseverance already has a sample in its "belly" waiting to be returned from Mars.

No matter how things develop, this discovery is an important chapter in the history of the search for extraterrestrial life and a test of scientists' research capabilities.

NASA first announced the discovery in a press conference last July, but provided few details.

The data presented at the conference came from a rock in the Jezero Crater on Mars, where the rover landed in 2021 to search for signs of Martian life. Millions of years ago, the crater may have hosted a lake that could have supported life, and the rock formed in the channel of an ancient river that once flowed into the lake.

The rock has both black, pepper-like spots, called seeds, and larger spots with lighter centers and darker edges, called stripes. Chemical analysis by instruments on the rover showed that both the seeds and the stripes are rich in iron and phosphorus at the edges. Joel Hurowitz, a geochemist at the State University of New York at Stony Brook, said at the conference that the center of the stripes is rich in iron and sulfur.

The concentration of these chemicals suggests that the seeds and leopard patterns formed when carbon-containing "organic" compounds in the rock reacted with iron and sulfate minerals. On Earth, this reaction is triggered by microorganisms.

If the rock is heated, these reactions could occur in the absence of life, but Hurowitz and his colleagues think this is not the case. The rock is fine-grained, indicating that it was not heated and recrystallized. Michael Tice, a geobiologist at Texas A&M University, pointed out at the meeting that if the rock temperature remains low, model studies show that these spots can easily form if organisms play a role in the process.

What is not yet clear is whether such reactions could occur in the absence of living organisms. "We feel it is necessary to do a lot of laboratory, field and model studies to explore these types of signatures in more detail," Hurowitz said at the meeting. "By bringing these samples back to Earth, we can conclude whether they were formed by life or not."

NASA is under pressure to bring 30 samples from Perseverance back to Earth, with early estimates that the mission would cost $11 billion. So far, the agency has not taken any action. If the samples make it to the lab, scientists can perform more complex analyses, such as isotope studies. This could help reveal whether microorganisms were involved in the formation of the spots.

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Source: China Science Daily

Editor: Yang Yaping

Proofread by Xu Lailinlin