Footage of what are called “tiger spots” on a rock known as the Chevaya Falls (and other similar rocks in the Bright Angel formation) may indicate biological processes, according to a comprehensive analysis conducted by geologist and planetary scientist Joel Horowitz from Stony Brook University in the United States. However, it cannot be confirmed until the sample collected by Perseverance is brought back to Earth for thorough study. Non-biological processes are still under investigation, but the evidence gathered by Horowitz and his colleagues is impressive.
Perseverance discovered the Chevaya Falls rocks just over a year ago as it crawled across the bottom of the Jezero Crater, a vast basin that was once filled with liquid water. Scientists were immediately intrigued, as on Earth, features similar to those seen on the rock are often associated with fossilized microbes.
Horowitz told the magazine, “Perhaps the mix of chemical compounds we found in the Bright Angel formation was a rich energy source for microbial metabolism, but the mere presence of all these attractive chemical signatures in the data does not necessarily mean there is a potential biosignature. We needed to analyze what this data could mean.”
According to Perseverance’s data, the samples it analyzed contained carbon-rich organic materials. There are many organic materials on Mars, and there are also many non-biological processes that can produce organic materials, meaning their presence is not diagnostic by itself. The rock also contained calcium sulfates, separated by layers of an iron-rich mineral called hematite. At the same time, the tiger spots were particularly rich in iron phosphate and iron sulfide, possibly minerals vivianite and greigite.
Phosphate has significant biological importance here on Earth, and both minerals could result from electrochemical redox reactions involving organic carbon, whether biological or abiotic. Mars is certainly capable of producing acidic conditions and high temperatures through volcanic activity. However, the Bright Angel rocks show no other signs of exposure to such a high level of heat, nor even a drop in acidity.
It will be challenging to learn more without studying the rocks themselves, as Perseverance’s toolkit is very limited compared to what geologists can accomplish here on Earth. Researchers are eagerly looking forward to obtaining the collected samples.
