NASA rovers looking for evidence of life make surprising revelations for the future of space mining as well.

In the last two months of an ongoing search for signs of ancient life on Mars, NASA's Perseverance and Curiosity have been wheeling around the red planet looking for rocks that may have been created or modified long ago by the presence of water and microbial life. Meanwhile, a rich volcanic history may produce other treasures as well.

A vein of spotted rocks nicknamed Cheyava Falls (after a Grand Canyon waterfall) patterned with marks like a leopard caught the attention of NASA's Perseverance mission team with fascinating traits that may finally answer the question of whether Mars was home to microscopic life in the distant past. The unique mottling could indicate that ancient chemical reactions once occurred within the rock and supported microbial organisms.

NASA/JPL-Caltech

Spotting of this type can occur when chemical reactions involving hematite turn the rock from red to white. These reactions can be an energy source for microbes.

"These spots are a big surprise," said David Flannery, member of the NASA Perseverance science team and an astrobiologist at the Queensland University of Technology in Australia, in a statement. "On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface."

Multiple scans by the rover's SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument indicate it contains organic compounds. While such carbon-based molecules are considered the building blocks of life, they can also be formed by non-biological processes. Perseverance's PIXL (Planetary Instrument for X-ray Lithochemistry) instrument has determined these black halos contain both iron and phosphate.

Other explanations are also being considered by the team, and the research is still preliminary. NASA scientists haven't yet determined whether ancient life is a valid explanation, which will require further study of the sample once it is returned to Earth.

NASA's Mars Sample Return Program, in cooperation with ESA (European Space Agency), is designed to send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for in-depth analysis.

"We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable," said Ken Farley, a Perseverance project scientist out of Caltech in Pasadena, California. "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."

While both the organic matter and the leopard spots are of great interest, there are also nearby veins filled with millimeter-sized crystals of olivine, a mineral that forms from magma.

"Cheyava Falls is the most puzzling, complex, and potentially important rock yet investigated by Perseverance," said Farley. "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. 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."

A pure sulfur curiosity

As Perseverance investigated clues of potential ancient microbial life, Curiosity made its most unusual find to date – rocks made of pure sulfur. This accidental discovery was made when the robot went to check up on a rock it had inadvertently crushed, revealing yellowish-green crystals never spotted before on the red planet.

NASA/JPL-Caltech

Curiosity rover accidently discovered pure sulfur crystals when the robot happened to drive over a rock and crack it open.

"I think it's the strangest find of the whole mission and the most unexpected," said Ashwin Vasavada, Curiosity project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena. "I have to say, there's a lot of luck involved here. Not every rock has something interesting inside."

Sulfates, or salts that contain sulfur that are formed when water evaporates, weren't new to the robotic explorer. The team has seen evidence of bright white calcium sulfate, also known as gypsum, within cracks on the Martian surface that are essentially hard-water deposits left behind by ancient groundwater flows.

"No one had pure sulfur on their bingo card," Vasavada said.

The Curiosity team was eager for the rover to investigate the Gediz Vallis channel, a winding groove that appears to have been created 3 billion years ago by a mix of flowing water and debris. The channel was carved into part of the three-mile-tall (or five kilometers) Mount Sharp, which the rover has been scaling since 2014.

The rover drivers at JPL, who sent instructions to Curiosity, made a 90-degree turn to put the robotic explorer in the right position for its cameras to capture the surrounding landscape. While doing this, the rover, which weighs one ton, had crunched a very special rock under its treads.

Members of the team were stunned twice – once when they saw the "gorgeous texture and color inside" the rock and then when they used Curiosity's instruments to analyze the rock and received data indicating it was pure sulfur, Vasavada said.

Every rover has revealed a new geological bonus. NASA's Spirit rover broke one of its wheels and had to drag it along while using the other five to drive backward. The dragging revealed bright white soil, which turned out to be nearly pure silica. The presence of silica suggests hot springs or steam vents may have once been on Mars, which also could have created conditions favorable for microbial life.

More to come

Perseverance is part of NASA's Moon to Mars exploration approach, which includes Artemis missions and will help prepare for human exploration of the Red Planet. The rover will characterize the planet's geology and past climate to help pave the way for human exploration of the Red Planet and as the first mission to collect and cache Martian rock and regolith.

Though Mars is smaller than Earth, its geology is often immense. The abundance of comparatively massive volcanic Martian features is strong evidence for a variety of ores that would be very useful to potential colonists and future space miners. For example, Olympus Mons, the largest of the Martian volcanoes, is roughly the size of Arizona and more than twice as tall as Everest here at home.

While nothing may yet justify the high cost of transporting material en masse back to Earth, as transport becomes less expensive and more potential ores are available, the more attractive it becomes for the future of space-resource industries. These elements might include the basics of copper, chromium, iron, and nickel, as well as significant amounts of niobium, lanthanum, neodymium, and europium.