A few of the recently collected samples include organic matter, indicating that Jezero Crater, which likely once held a lake and the delta that emptied into it, had potentially habitable environments 3.5 billion years ago.
“The rocks that we have been investigating on the delta have the highest concentration of organic matter that we have yet found on the mission,” said Ken Farley, Perseverance project scientist at the California Institute of Technology in Pasadena.
The rover’s mission, which began on the red planet 18 months ago, includes looking for signs of ancient microbial life. Perseverance is collecting rock samples that could have preserved these telltale biosignatures. Currently, the rover contains 12 rock samples.
Digging into the delta
The site of the delta makes Jezero Crater, which spans 28 miles (45 kilometers), of particularly high interest to NASA scientists. The fan-shaped geological feature, once present where a river converged with a lake, preserves layers of Martian history in sedimentary rock, which formed when particles fused together in this formerly water-filled environment.
The rover investigated the crater floor and found evidence of igneous, or volcanic, rock. During its second campaign to study the delta over the past five months, Perseverance has found rich sedimentary rock layers that add more to the story of Mars’ ancient climate and environment.
“The delta, with its diverse sedimentary rocks, contrasts beautifully with the igneous rocks — formed from crystallization of magma — discovered on the crater floor,” Farley said.
“This juxtaposition provides us with a rich understanding of the geologic history after the crater formed and a diverse sample suite. For example, we found a sandstone that carries grains and rock fragments created far from Jezero Crater.”
The mission team nicknamed one of the rocks that Perseverance sampled as Wildcat Ridge. The rock likely formed when mud and sand settled in a saltwater lake as it evaporated billions of years ago. The rover scraped away at the surface of the rock and analyzed it with an instrument known as the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals, or SHERLOC.
This rock-zapping laser functions as a fancy black light to uncover chemicals, minerals and organic matter, said Sunanda Sharma, SHERLOC scientist at NASA’s Jet Propulsion Laboratory in Pasadena.
The instrument’s analysis revealed that the organic minerals are likely aromatics, or stable molecules of carbon and hydrogen, which are connected to sulfates. Sulfate minerals, often found sandwiched within the layers of sedimentary rocks, preserve information about the watery environments they formed in.
Organic molecules are of interest on Mars because they represent the building blocks of life, such as carbon, hydrogen and oxygen, as well as nitrogen, phosphorous and sulfur. Not all organic molecules require life to form because some can be created through chemical processes.
“While the detection of this class of organics alone does not mean that life was definitively there, this set of observations does start to look like some things that we’ve seen here on Earth,” Sharma said. “To put it simply, if this is a treasure hunt for potential signs of life on another planet, organic matter is a clue. And we’re getting stronger and stronger clues as we’re moving through our delta campaign.”
Perseverance as well as the Curiosity rover has found organic matter before on Mars. But this time, the detection occurred in an area where life may have once existed.
“In the distant past, the sand, mud, and salts that now make up the Wildcat Ridge sample were deposited under conditions where life could potentially have thrived,” Farley said.
“The fact the organic matter was found in such a sedimentary rock — known for preserving fossils of ancient life here on Earth — is important. However, as capable as our instruments aboard Perseverance are, further conclusions regarding what is contained in the Wildcat Ridge sample will have to wait until it’s returned to Earth for in-depth study as part of the agency’s Mars Sample Return campaign.”
Returning samples to Earth
The samples collected so far represent such a wealth of diversity from key areas within the crater and delta that the Perseverance team is interested in depositing some of the collection tubes at a designated site on Mars in about two months, Farley said.
Once the rover drops off the samples at this cache depot, it will continue exploring the delta.
Future missions can collect these samples and return them to Earth for analysis using some of the most sensitive and advanced instruments on the planet. It’s unlikely that Perseverance will find undisputed evidence of life on Mars because the burden of proof for establishing it on another planet is so high, Farley said.
“I’ve studied Martian habitability and geology for much of my career and know first-hand the incredible scientific value of returning a carefully collected set of Mars rocks to Earth,” said Laurie Leshin, director of NASA’s Jet Propulsion Laboratory, in a statement.
“That we are weeks from deploying Perseverance’s fascinating samples and mere years from bringing them to Earth so scientists can study them in exquisite detail is truly phenomenal. We will learn so much.”
Some of the diverse rocks in the delta were about 65.6 feet (20 meters) apart, and they each tell different stories.
One piece of sandstone, called Skinner Ridge, is evidence of rocky material that was likely transported into the crater from hundreds of miles away, representing material that the rover won’t be able to travel to during its mission. Wildcat Ridge, on the other hand, preserves evidence of clays and sulfates that layered together and formed into rock.
Once the samples are in labs on Earth, they could reveal insights about potentially habitable Martian environments, such as chemistry, temperature and when the material was deposited in the lake.
“I think it’s safe to say that these are two of the most important samples that we will collect on this mission,” said David Shuster, Perseverance return sample scientist at the University of California, Berkeley.