MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images
MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images
NASA’s Perseverance rover has discovered diverse and abundant organic molecules—the building blocks for life—in the ancient Martian lakebed where it landed two years ago, reports a new study. The rover has detected organic matter in practically every target it has studied, including compounds that appear to have different origins, hinting at a more complex chemical history on Mars than was previously known. The presence of organic molecules at Perseverance’s landing site, Jezero Crater, does not prove that aliens ever existed on Mars since they can emerge from abiotic processes, though it offers tantalizing clues about the planet’s habitability billions of years ago, when it was warmer, wetter, and evidently rich in the ingredients for life. But, researchers aren’t ruling it out.
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“The presence of organic material in Jezero is a promising hint towards past habitability,” said Joseph Razzell Hollis, a research fellow at the Natural History Museum in London, U.K. who co-authored the study, in an email to Motherboard. “The fact that organics are so ubiquitous, appearing in so many of the targets we studied, even after billions of years of exposure to radiation and oxidation, hints at the possibility that Jezero Crater was abundant in organics when water still flowed through the crater 3-4 billion years ago, around the same time life evolved on Earth.” Since it landed on Mars in February 2021, Perseverance has traveled nearly 12 miles across Jezero Crater, a region that was brimming with water in the deep past. The rover is equipped with an instrument called the Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) that can spot the “fluorescence” signatures of organic matter in Martian rocks. Organic molecules contain carbon and can be made by a number of different geological and biological processes.Hollis and his colleagues now report that Perseverance has detected a range of different “aromatic” organic compounds, which have ring-like internal structures, at the Máaz and Séítah formations of Jezero Crater. The discovery suggests that “there may be a diversity of aromatic molecules prevalent on the Martian surface” that potentially indicate “different fates of carbon across environments,” according to the team’s study, which was published on Wednesday in Nature.
“As our paper shows, we detected exciting fluorescence signatures pretty much the first time we used SHERLOC in Jezero, and in most of the rocks we’ve looked at since,” said Hollis, who is a member of the SHERLOC team. “It was a huge deal for us on the team, we were actually seeing something using an analytical technique that’s never been used on another planet before!” “Then came the long process of proving to ourselves and others that what we were seeing was real, and most likely organic in origin,” he continued. “The challenge of doing something new on Mars meant that we weren’t entirely sure what we expected to see going in, but the sheer variety of signatures we have observed so far is really exciting, and to see them varying with geological context—it suggests that there are a lot of different kinds of organics present in Jezero, some may come from the rock itself and some may have been added or altered later by the flow of water.”The discovery of such a varied array of organic compounds opens a new window into the conditions at Jezero Crater more than 3.5 billion years ago. In this bygone era, the crater hosted a river and a lake that converged to form a sweeping fan-like delta where sediments piled up over time. Perseverance is now exploring the desiccated remains of this delta and drilling out core samples that scientists hope to retrieve with a future mission called Mars Sample Return (MSR). While the rover can perform a preliminary analysis of Martian rocks with its onboard instruments, scientists will need to bring the core samples back to Earth to definitively determine whether they contain “biosignatures,” which are signs of life.
“The challenge of detecting biosignatures is that the burden of proof is very high, and for good reason,” Hollis said. “Organic material can occur naturally through simple geochemical and astrochemical processes” and “many of the most basic building blocks of life occur naturally in completely abiotic places like meteorites and nebulae, and so the question becomes about what doesn’t make sense about the sample if you assume a purely abiotic origin.” “Organic material that is too complex, too organized, or too concentrated to be explained by purely abiotic processes—that is when we start wondering about possible biological origins,” he added. “We often call it the ‘hypothesis of last resort’ for that reason.” To that point, Hollis and his colleagues proposed numerous abiotic explanations for the organic compounds that the rover detected at Máaz and Séítah, though they don’t rule out a biotic origin for the molecules. Ancient interactions between water and the basaltic landscape of Jezero Crater may have forged the diverse array of organics in various ways. The team noted that organic matter is more concentrated at Máaz by an order of magnitude, suggesting that the site’s compounds were made by different processes than those at Séítah. Perseverance’s findings build on similar discoveries made by its predecessor, Curiosity, which is still exploring Mars’ Gale Crater more than a decade after it landed there in 2012. Curiosity is about 2,300 miles away from Perseverance, but it also found organic molecules at its site, demonstrating that Mars once had the right conditions to support life. Now, Perseverance has added a new chapter in the search for life on Mars with its detection of wide-ranging organic matter in Jezero Crater.
“Every rock we scan with SHERLOC provides us with another little glimpse into the organics that were present when that delta was deposited, and helps us build up a bigger picture,” Hollis said. “It’s a lot like a jigsaw really, each piece is tiny and starts off meaningless, but as you collect and compare them you start to see patterns that connect pieces together.” “This will just the first of many papers that will be published about organics in Jezero Crater, all thanks to SHERLOC, and every paper will bring us a little closer to a more complete understanding of what organic material was present in Jezero billions of years ago, and whether or not it was purely abiotic in origin,” he noted.Assuming everything goes to plan, the forthcoming MSR mission will pick up Perseverance’s carefully cached samples within the next decade, and haul them back to Earth sometime in the 2030s. These extraterrestrial materials could finally answer one of humanity’s most essential questions: Are we alone in the universe? If scientists can unambiguously detect signs of extraterrestrial fossils in the returned samples, it might suggest that simple forms of life may commonly arise on other worlds across the galaxy. And while it's mind-boggling to imagine that we might find alien traces in the precious Mars rocks, Hollis pointed out that any outcome of this interplanetary endeavor would help humans understand our place in the universe.“Even if we bring back the samples with MSR and cannot find any evidence for biological origins, there are still so many exciting questions we can ask about what we have found,” he concluded. “For example, why did life evolve on Earth, but not on Mars? What ingredients does life need to evolve? These questions are just as important as ‘was there life on Mars?’ and will keep astrobiologists busy for decades.”