NASA's Perseverance rover may have discovered signs of ancient life in a rock on Mars, although scientists say further research is needed.
The rover collected a sample from an arrowhead-shaped reddish rock, nicknamed Cheyava Falls after a waterfall at the Grand Canyon, on July 21.
Analysis by the rover revealed that the rock possesses "fascinating traits" and features that could suggest Mars was once home to microscopic life.
For example, it shows chemical signatures and structures that might have been created by life billions of years ago.
Inside the rock, organic compounds were also detected. While such carbon-based molecules are considered the building blocks of life, they can also be formed by non-biological processes.
In its quest to find signs of ancient microbial life, the Perseverance mission has concentrated on rocks that might have been formed or altered by water long ago. This focus is why the team selected Cheyava Falls for closer examination.
"We have designed the route for Perseverance to ensure that it goes to areas with the potential for interesting scientific samples," Nicola Fox, associate administrator, Science Mission Directorate at NASA Headquarters in Washington, said in a statement. "This trip through the Neretva Vallis riverbed paid off as we found something we've never seen before, which will give our scientists so much to study."
The fascinating rock also features large white veins of calcium sulfate running through it. Between these veins are bands of reddish material—which likely contain hematite—a mineral responsible for Mars' characteristic rusty color.
After examining these red areas more closely, the team discovered numerous irregularly shaped, millimeter-sized off-white splotches, each bordered by black rings, resembling leopard spots and containing both iron and phosphate.
"These spots are a big surprise," David Flannery, astrobiologist and member of the Perseverance science team, said in a statement. "On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface."
Ken Farley, a scientist involved in the project, also described Cheyava Falls as the most puzzling, complex, and potentially significant rock yet investigated by Perseverance.
"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," he said in a 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."
The distinctive spotting found on the rock can occur when chemical reactions involving hematite turn rock from red to white.
Those reactions can also release iron and phosphate, possibly causing the black halos to form. Reactions of this type can be an energy source for microbes, explaining the association between such features and microbes in a terrestrial setting.
One scenario the Perseverance science team is considering is that Cheyava Falls was initially deposited as mud containing organic compounds, which later hardened into rock. Subsequently, a second episode of fluid flow infiltrated cracks in the rock, leading to the formation of the large white calcium sulfate veins and the distinctive spots seen today.
In addition to the organic matter and leopard spots, scientists were surprised to find that the veins are filled with millimeter-sized crystals of olivine, a mineral that forms from magma.
This olivine could be linked to rocks that originated higher up in the river valley, potentially formed by magma crystallization. The team now faces another question: Could the olivine and sulfate have been introduced to the rock at extremely high temperatures, leading to an abiotic chemical reaction that created the leopard spots?
"We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable," Farley said. "Scientifically, Perseverance has nothing more to give. To fully understand what really happened in that Martian river valley at Jezero Crater billions of years ago, we'd want to bring the Cheyava Falls sample back to Earth, so it can be studied with the powerful instruments available in laboratories."
A key objective of Perseverance's mission on Mars is astrobiology, particularly the collection of samples that could contain evidence of ancient microbial life.
The rover will also study the planet's geology and past climate, which will help prepare for future human exploration of Mars. Perseverance is the first mission to date to collect and cache Martian rock and regolith for future analysis.
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