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The NASA Perseverance rover may have found a pivotal clue that’s central to its mission on Mars: geological evidence that could suggest life existed on the red planet billions of years ago.
The robotic explorer came across a vein-filled red rock on July 18 that appears to be scattered with leopard spots. The mottling could indicate that ancient chemical reactions occurring within the rock once supported microbial organisms.
“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.”
The research is still preliminary, and NASA scientists haven’t yet confirmed how the rock was created, which would require studying it on Earth. But the arrowhead-shaped specimen could help the Perseverance team unlock whether Mars was once a planet hospitable to life.
“We’re absolutely thrilled to have this sample in the bag!” said Briony Horgan, co-investigator on the Perseverance rover mission and professor of planetary science at Purdue University in West Lafayette, Indiana, in an email.
“This rock is exactly the type of sample that we came to Mars to find, and we can’t wait to get it into our labs back here on Earth,” she said. “This is precisely the type of potential microbial biosignature that was envisioned when NASA designed the Mars 2020 mission, and we’ve used every instrument in our payload to find and understand this rock.”
The search for signs of ancient life on Mars
The rock, nicknamed Cheyava Falls for one of the Grand Canyon’s waterfalls, intrigues scientists for multiple reasons.
White veins of calcium sulfate present clear evidence that water — crucial for life — once ran through the rock. The rover used its Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals, or SHERLOC, instrument to identify organic carbon-based molecules within the rocks.
And the irregular-shaped leopard spots, tested by the rover’s PIXL instrument, short for Planetary Instrument for X-ray Lithochemistry, detected iron and phosphate within the features, said Morgan Cable, a research scientist on the rover team, in a video shared by NASA’s Jet Propulsion Laboratory in Pasadena, California.
“We’ve never seen these three things together on Mars before,” Cable said.
The team also spotted the potential presence of hematite between the white bands of calcium sulfate in the rock. Hematite is one of the minerals responsible for Mars’ signature red hue.
The leopard spotting may have occurred when chemical reactions with hematite turned the rock from red to white, which can release iron and phosphate and potentially cause the black rings to form. Such reactions can also provide an energy source for microbes.
“Cheyava Falls is the most puzzling, complex, and potentially important rock yet investigated by Perseverance,” said Ken Farley, Perseverance project scientist and professor of geochemistry at the California Institute of Technology in Pasadena, in a statement.
The team also discovered millimeter-size crystals of olivine within the same rock. Olivine, previously detected in another part of the crater by Perseverance, is a mineral that forms from magma. The olivine present in the Cheyava Falls rock could be related to rocks that formed at a different place in the valley, according to the team.
The rover team is grappling with a multitude of questions as they study the rock and try to determine what processes could have formed it.
Cheyava Falls may have begun as a mixture of deposited mud and organic compounds that eventually cemented to become rock. Later on, water may have penetrated through cracks in the rock, depositing minerals to create the calcium sulfate veins and leopard spots.
But it’s also possible that the olivine and sulfate became part of the rock due to scorching hot temperatures on Mars, causing a non-biological chemical reaction that created the leopard spots.
Exploring Mars’ past
Since landing on Mars, Perseverance has crossed Jezero Crater and explored an ancient river delta in search of microfossils of past life. The rover has been collecting samples along the way that could be returned to Earth by future missions.
More recently, Perseverance has been exploring the northern edge of Neretva Vallis, an ancient river valley that once delivered water into Jezero Crater more than 3 billion years ago, and that’s where it spotted Cheyava Falls. The rover landed within the crater to explore the ancient lake site in February 2021.
Geologists on the rover team have been eager for Perseverance to study rocks that were either created or modified by water on Mars in the past, which is why Cheyava Falls intrigued them.
“We have designed the route for Perseverance to ensure that it goes to areas with the potential for interesting scientific samples,” said Nicola Fox, associate administrator for NASA’s Science Mission Directorate, 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 hard road to finding proof of life
In April, NASA said the original complex, multimission design for the program intended to return Perseverance’s samples to Earth, called Mars Sample Return, was no longer feasible in its current architecture due to budget cuts and a delayed return date.
The agency has opened up a call to NASA centers and industry to develop a new plan that combines innovation with lessons learned from proven technology. It is the hope of NASA leadership to return the samples to Earth by the 2030s with less complexity, cost and risk than originally planned, and the agency is expecting to have answers for how best to return samples from Mars by the fall, said NASA administrator Bill Nelson during an April news conference.
Meanwhile, Perseverance continues its crucial investigative work on Mars and will begin climbing the rim of Jezero Crater soon.
“This discovery has come at such a critical time, while NASA is reconsidering the best way to get these samples back from Mars via Mars Sample Return,” Horgan said. “It shows just how important and unique our suite of samples (is) and just how much we could learn about the beginnings of life on Earth-like planets. It also feels very fitting that Jezero threw us one final surprise before we leave the ancient river and lake sediments of the crater floor and start climbing the rim.”
The Perseverance team says returning the samples is the only way to know whether life ever existed on Mars.
“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.”