NASA'shas collected and stored samples of rocks made up of minerals and organic compounds that, on Earth, would likely preserve traces of past microbial life, researchers said Thursday. The soil samples were gathered at the base of an ancient river delta fanning out from the rim of .
But to find out if any such "potential biosignatures" include actual traces of past life on Mars, scientists will have to wait for a NASA-European Space Agency mission at the end of the decade to collect them and bring them back to Earth for detailed laboratory analysis.
"The samples that we've collected as we presented here today ... have ingredients for life in terms of the environmental setting," said David Shuster, a Perseverance return sample scientist at the University of California.
The material was long ago transported into Jezero Crater by water and deposited into a 25-mile-wide lake with fine particles that settled out amid phases of evaporation — factors that combine to "have high potential for biosignature preservation."
"If these conditions existed, I think, pretty much anywhere on Earth at any point in time over the last ... three and a half billion years, I think it's safe to say, or at least assume, that biology would have done its thing and left its mark in these rocks for us to observe.
"And so that's really why we're so excited to be able to address these questions upon returning these samples to laboratories here on Earth," Shuster said. "We have all of the right ingredients here."
The $2.4 billion Perseverance roveron February 18, 2021, and has spent the past 18 months working its way toward the base of a fan-like delta cutting through the rim where water once rushed in to fill a broad, now-vanished pool the size of Lake Tahoe.
Perseverance is equipped with a suite of sophisticated instruments designed to study the ancient lakebed deposits, on the lookout for traces of past microbial life that might have filtered down to be preserved in what are now layers of sedimentary rock.
Along with giving scientists an opportunity to remotely survey the rocks and sandy soil of Jezero, Perseverance also is equipped with a complex collection and caching mechanism that can store more than 40 samples of soil and rocky cores, sealing them in small environmentally closed tubes to await transport back to Earth.
If all goes well, a joint sample return mission being developed by NASA and the European Space Agency will land another spacecraft near Perseverance around 2030 and either collect the stored samples from the rover or use two small helicopters to pick up sample tubes Perseverance will have dropped onto the surface.
The samples will be loaded onto a small rocket and blasted into Mars orbit where they will be captured by another spacecraft and returned to Earth for analysis to determine if any of the "potential biosignatures" are actual traces of past microbial life.
"Mars sample return stands maybe the best chance ever of answering a very profound question: are we alone in the universe?" said Sunanda Sharma, a researcher at the Jet Propulsion Laboratory who works with one of the rover's instruments.
Perseverance has been operating in near flawless fashion since its landing 559 Mars days ago. In an early surprise, the rover found igneous rock well away from the rim of Jezero Crater where scientists had expected to find sedimentary lakebed layers.
"What we found is igneous rocks, rocks that were crystallized from a melt," said Project Scientist Ken Farley. "This crater not only held the lake at one point, but prior to that, likely prior to that, it also had active volcanism, and possibly even a lava lake filling that crater. So there's some complexity there that we hadn't actually expected."
After collecting samples of the igneous deposits, which will allow scientists to eventually determine how old the formations are, Perseverance headed toward the the base of the delta and found the sedimentary deposits it was looking for.
"This specific area has probably the highest scientific value for exploration of the entire mission," Farley said. "This is the site that brought us to Jezero Crater. This is the place where we have the best chance to explore these ancient sedimentary rocks deposited in the lake."
The rocks there "were deposited in a potentially habitable environment ... and we have been seeking potential biosignatures."
But he quickly cautioned that "a potential biosignature is something that may have been produced by life, but also could have been produced in the absence of life. The key point about a potential biosignature is it compels further investigation to draw a conclusion."
And that further investigation is laboratory analysis on Earth after the sample return mission gets back in the early 2030s.
Perseverance has collected a dozen samples to date, along with a sample of the martian atmosphere and two "witness tubes" to help assess any contamination that might be present. The tubes are stored in the body of the rover, and the science team is debating where to deposit an initial cache for later retrieval by the sample return lander.
The rover eventually will climb up on top of the delta before making its way to the shore of the ancient lake, collecting more samples along the way. Assuming Perseverance stays healthy, it will rendezvous with the sample return lander and hand off its trove of samples.
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