In November 2022, Matthew Genge was looking through an electron microscope when he noticed something off a millimeter-sized spot on the asteroid Ryugu. A small, yet unmistakable, rod-like pan of organic matter unseen before was stuck to the surface. “I thought, ‘Well, that’s weird,'” Geng recalls. “Then I found another and another.”
For a brief moment, he and his colleagues reflected that they had just made perhaps the most momentous discovery in human history: the discovery of alien life imported to Earth in a few grams of material extracted from a space rock. The Japan Aerospace Exploration Agency (JAXA) had the Hayabusa2 mission captured the samples in 2019 and delivered them Australia to a remote touch point in an airtight capsule next year. JAXA scientists then cataloged Individual particles have been collected using sterilized instruments in state-of-the-art clean rooms and sent to researchers around the world—including Genge’s team—in sealed containers filled with nitrogen.
But if the tiny threads were aliens, they must have been hungry and behaving terrestrial microbes, feeding Ryugu’s tiny patch of nutrients to increase their numbers 10-fold before dying under the bombardment of scanning electron microscope measurements. curious scientists Observing the up-and-down cycle, Genge and his colleagues realized that they were almost certainly terrestrial invaders that had somehow colonized the small alien sample despite the researchers’ strict precautions. Humbled, they dutifully wrote down their findings, which they were published last month “It’s a bit of a shame,” says Genge, a planetary scientist at Imperial College London. “But as a scientist, you have to tell the truth; it’s important to report these things.”
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A case for careful watch
That the Ryugu grains provided a generous buffet for Earth’s microorganisms comes as no surprise to scientists studying such primitive asteroids, which are typically littered with carbon-rich organic molecules. The event, however, is a reminder that even the strictest protocols cannot always prevent land contamination. “I don’t think this is a failure of the team, but rather that working under conditions that cannot guarantee sterility is an inevitable consequence of doing business on Earth,” says astrobiologist Andrew Steele of Carnegie Science, who was not involved in the new study. The space agencies and scientists working with the samples make every effort to avoid contamination, and the fact that such intrusions can be detected even in a small particle is a testament to advanced technology and rigorous screening methods. “But at the end of the day, we live on a planet ruled by microbes, and random events happen,” Steele says, so this episode “provides us with new ways to learn and learn.”
One lesson is that changes in the handling of a grain are dangerous. When Genge and his team first examined the specimen in October 2022, there was no sign of bacteria, suggesting that the contamination likely did not occur because of a slip in JAXA’s rigorous process, but rather during a necessary preparation step in a Natural History Museum laboratory. London, where researchers removed the specimen from the container for analysis. “We were pretty careful about it, but nobody was as careful as JAXA, because we don’t have a facility,” Geng says. “You only need one bacterial cell to fall on your grain, and that’s it, it’s infected.”
The case underscores “the importance of curatorship and that it is worth the great effort we put into mission development to maintain these high standards,” says JAXA’s Toru Yada, who directs sample care on the Hayabusa2 mission and published it. the papers about the rigorous process. Those measures, which also include the construction, launch and recovery of spacecraft, make it extremely difficult to contaminate the agency’s facilities, but the risk inevitably increases when samples are sent to scientists around the world who don’t have similar infrastructure. “And (scientists from around the world are) the ones who would make the discoveries,” Geng says. “If you’re misinterpreting a contaminant as part of the sample, that becomes dangerous: you start polluting the science with the wrong assumptions.”
Genge’s best guess is that the rod-like filaments in the Ryugu grain belonged to a genus of microbes. Bacillus. These hardy bacteria are known for their ability to quickly survive in new extreme environments. Firm identification by DNA testing, however, was not attempted because the suspected microbes were effectively trapped under a carbon coating applied for analysis. Various the experiments meteorites have shown that extraterrestrial material is rich in organic matter to support life as we know it, sometimes for years. But microbes can survive on so little that, unless they reach very large populations, they usually don’t change the composition of a rock enough for scientists to find it easily. The microfossils they leave behind can be valuable clues to their presence, but they distinguish true microfossils. abiotic processes who can imitate them is not an easy task and has before it sparked heated debates.
“If we found microfossils—insert your favorite world—it could be a potential indicator of life,” says astrobiologist Manasvi Lingam of the Florida Institute of Technology, who was not affiliated with the new work. But the case of the contamination of the Ryugu sample shows that “if we find these structures, we have to be careful not to let humans in somehow.”
Only a decade ago, scientists blamed poor clean room etiquette for allowing bacteria common in nasal phlegm. enter NASA’s Surveyor 3 spacecraftIn the 1960s fragments traveled to the Moon and returned to Earth. Technology and protocols have advanced greatly over the years to help keep both cleanrooms and otherworldly explorations as clean as possible. Even so, scientists will undoubtedly continue to ask similar difficult questions as they search for signs of alien life in samples returned with icy satellites from the moon, Mars and, perhaps someday, the giant planets of the outer solar system.
If it belongs to NASA The messy Mars Sample Return (MSR) program is successful, for example, scientists hope to study carefully selected parts his understanding of the world life prospects. “Not only are we expecting rich organic samples, but we are preparing for potential biosignatures,” the MSR team said. American scientific. “Therefore, in addition to improved cleaning protocols, comprehensive sterilization of equipment and instruments will be required, which are part of (the European Space Agency’s) ongoing research and development efforts with our partners.”
Closer to home, the moon is so used by most organisms for energy that microbial contamination is of little concern to scientists working with Apollo-era lunar samples. That could change in the future with efforts like NASA’s Artemis III lunar sampling missions bring back material from slightly more hospitable regions, for example craters filled with ice of the south pole of the moon. All these samples would be prepared in clean environments and loaned to licensed scientists subject to security requirements. “NASA has been an extraordinary custodian of the Apollo samples,” says geologist Darby Dyar of Mount Holyoke College, who is studying some of the remaining pristine Apollo samples.
Also, as JAXA’s Martian Moons eXploration (MMX) mission prepares to return samples from Phobos, a Martian moon, in 2026, Yada says the agency has begun monitoring the environment where the spacecraft is being built and is developing one. the protocol to handle returned samples. “We publish these steps to share our curation procedures with the global community … so that researchers who receive samples can be sure how they were handled, which is essential for interpreting scientific results,” he says.
The agencies do not mandate specific infrastructure or procedures for organizations that borrow alien samples, including for managing microbial contamination. “They’re everywhere,” Dyar says of microbes. “From a scientific perspective, you do the best you can.” Thanks to advances in technology and screening tools, scientists are able to study complex nuances of biotic and abiotic chemistry that were unimaginable just a decade ago. However, could we be fooled by mistaking plain old earth microbes or their lifeless remains for alien life forms?
“It’s something we’ve struggled with in the Mars community for a long time,” Steele says. “The short answer is no, unless alien life closely resembles life on Earth.”
