A few of the recently collected samples contained organic material, indicating that the Jezero Crater, which probably once contained a lake and the delta that emptied into it, had possibly habitable environments 3.5 billion years ago.
“The rocks we examined in the delta have the highest concentration of organic matter we’ve found during the mission to date,” 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, involves searching for signs of ancient microbial life. Perseverance is collecting rock samples that could to have save this telltale bio signatures. Currently, the rover contains 12 rock samples.
Digging in the delta
The location of the delta makes Jezero Crater, which is 45 kilometers long, special great interest in NASA scientists. The fan-shaped geologic feature, once present where a river met a lake, preserves layers of Martian history in sedimentary rock, which formed when particles fused in this previously water-filled environment.
The rover examined the crater floor and found traces of igneous or volcanic rock. During its second campaign to study the delta in 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 by crystallization of magma — discovered at the crater floor,” Farley said.
“This juxtaposition gives us a rich understanding of the geological history after the crater formed and a diverse array of samples. For example, we found a sandstone with grains and rock fragments made far from Jezero crater.”
The mission team named one of the rocks Perseverance sampled 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 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 expose chemicals, minerals and organic matter, said Sunanda Sharma, a 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, associated with sulfates. Sulfate minerals, often found in the layers of sedimentary rock, store information about the aqueous environments in which they formed.
Organic molecules are important on Mars because they represent the building blocks of life, such as carbon, hydrogen and oxygen, as well as nitrogen, phosphorus and sulfur. Not all organic molecules need life to form, as some can be created by chemical processes.
“While the detection of this class of organics alone doesn’t mean life was definitively there, this series of observations is starting to resemble some of the things we’ve seen here on Earth,” Sharma said. “To put it simply, if this is a search for possible signs of life on another planet, organic matter is a clue. And we’re getting stronger clues as we go through our delta campaign.”
Both Perseverance and the Curiosity rover have previously found organic material on Mars. But this time, the detection took place in an area where life once existed.
“In the distant past, the sand, mud and salts that now make up the Wildcat Ridge monster were deposited under conditions where life could potentially have thrived,” Farley said.
“The fact that the organic matter was found in such a sedimentary rock – known for preserving fossils of ancient life here on Earth – is important. However capable our instruments aboard Perseverance are, further conclusions about what might be in the Wildcat Ridge sample will have to wait for it to return to Earth for in-depth research as part of the agency’s Mars Sample Return campaign.”
Send monsters back to Earth
The samples collected so far represent such a wealth of diversity from key areas in the crater and delta that the Perseverance team is interested in depositing some of the collection tubes at a designated spot on Mars within about two months, Farley said. .
Once the rover has dropped off the monsters 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 in the world. Perseverance is unlikely to find undisputed evidence of life on Mars because the burden of proof to locate it on another planet is so high, Farley said.
“I’ve spent much of my career studying the habitability and geology of Mars and know firsthand 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.
“It’s truly phenomenal that we’ve deployed Perseverance’s fascinating samples for weeks and brought them to Earth for just a few more years so scientists can study them in great detail. We’ll learn so much.”
Some of the various rocks in the delta were about 20 meters apart and they each tell a different story.
A piece of sandstone called Skinner Ridge is evidence of rocky material likely transported hundreds of miles away into the crater, representing material that the rover cannot travel to during its mission. Wildcat Ridge, on the other hand, preserves evidence of clay and sulfates that layered together and formed rock.
Once the samples are in labs on Earth, they can 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 these are two of the most important samples we’ll be collecting on this mission,” said David Shuster, a Perseverance return sample researcher at the University of California, Berkeley.