NASA(NASA)'s "Perseverance" Mars rover recently discovered possible signs of ancient life. Scientists say this is one of the strongest evidence yet of life on Mars. Researchers said at the Lunar and Planetary Science Conference held in Texas, USA, on March 12,"Leopard patterns" on a rock studied by the rover last year may be remnants of microbial activity on Mars.
But while these "leopard spots" look a lot like spots produced by Earth's microbes, 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 may be at work.
For now, the discovery still scores a 1 on a scale of 1 to 7 for assessing alien life - 1 being an interesting signal detected and 7 being absolute confirmation. Jim Green, the former chief scientist at NASA who developed the classification, said he hopes researchers can conduct additional confirmation to move it to a higher classification. To do this, the "leopard" rocks would need to be brought back to Earth for analysis. There is already a sample in the "belly" of "Perseverance", waiting to return from Mars.
No matter how things develop, this discovery is an important step in the history of searching for extraterrestrial life, and it is also a test of scientists' research capabilities.
NASA first disclosed the discovery at a press conference in July last year, but almost no details were included.
The data presented at the meeting came from a rock from Jezero Crater on Mars. In 2021, a rover will land there to search for signs of life on Mars. Billions of years ago, there may have been a lake in this crater that was conducive to life, and this rock was formed in the channel of an ancient river that once flowed into the lake.
The rock has both black, pepper-like spots, known as "seeds," and larger spots with lighter centers and darker edges, known as "leopard spots." Chemical analysis by instruments on the rover showed that the edges of both the Seed and the Leopard are rich in iron and phosphorus. Joel Hurowitz, a geochemist at the State University of New York at Stony Brook, said at the meeting that the center of the "leopard pattern" is rich in iron and sulfur.
The enrichment of these chemicals suggests that the "seeds" and "leopard patterns" form when carbon-containing "organic" compounds in the rock react with iron and sulfate minerals. On Earth, this reaction is triggered by microorganisms.
If the rock was heated, these reactions might occur without life, but Hurowitz and colleagues don't think that's the case. Because the rock is fine-grained, it indicates that it has not been heated and recrystallized. Michael Tice, a geobiologist at Texas A&M University in the United States, pointed out at the meeting that when rock temperatures remain low, modeling studies show that these spots can easily form if organisms play a role in the process.
What's not clear is whether this reaction can occur in the absence of an organism."We feel the need to do a lot of laboratory, field and model studies to explore these types of features in more detail," Hurowitz said at the meeting. "By bringing these samples back to Earth, we can draw conclusions about whether they were formed by life."
NASA is facing tremendous pressure to bring the 30 samples from Perseverance back to Earth, with early estimates that the mission will cost $11 billion. So far, the agency has taken no action. If the sample can successfully get into the lab, scientists can perform more sophisticated analyses, such as isotope studies. This could help reveal whether microorganisms are involved in the formation of spots.