Strange DNA found in the desert offers lessons in the search for life on Mars End-shutdown


The Atacama Desert in Chile is almost the driest place on Earth. In some parts, it looks a lot like Mars. But it is not lifeless, even in hyper-arid regions. Using state-of-the-art equipment to probe desert rocks, researchers found DNA fragments from a intriguing mix of microbes.

A staggering 9 percent of genetic fragments belong to organisms unknown to science, making them part of the “dark microbiome,” according to a report released Tuesday in the journal Nature Communications.

These organisms are bacteria that are “so strange and different,” as the report says, that the researchers were unable to identify any known relatives.

“In almost half of the cases, the databases couldn’t clearly tell what we had on our hands,” lead researcher Armando Azua-Bustos, a microbiologist at the Center for Astrobiology in Madrid, told The Washington Post.

And that brings him back to the Mars analogy: The Atacama, he and his fellow scientists believe, is a brilliant test bed for the search for Martian life. But the same search conducted with versions of the instruments on today’s Mars rovers could barely detect any microbial signatures. That means it will be difficult to find conclusive evidence of present or past life in Martian soils without bringing samples back to Earth, Azua-Bustos and his colleagues concluded.

The research appears to bolster the long-term Mars exploration strategy of NASA and its partner, the European Space Agency. They are in the middle of a multi-stage mission called Mars Sample Return. If all goes according to plan, samples of Martian soil obtained by NASA’s Perseverance rover, which just celebrated its second anniversary on Mars, will be transported back to Earth early next decade for analysis in laboratories at high containment.

But this new research also highlights the challenges facing scientists who want to learn the (conjectured) biological history of Mars. Microbial life, especially if long extinct and fossilized, may exist at the furthest limit of what can be detected with the kind of instruments small enough to be launched into space and land on another planet.

Scientists have never found an example of life beyond Earth, but a general assumption is that “habitable” worlds will be inhabited, that life emerges, somehow, under the right conditions. The Red Planet has long tantalized astrobiologists. It was most like Earth about 3 billion years ago, when it had a thicker atmosphere and liquid water on the surface. Possibly, there is still cryptic life on Mars, although astrobiologists would be delighted to find even a microfossil of something that lived billions of years ago.

NASA’s 1976 Viking mission carried out experiments designed to detect life, and one offered an initially promising signal, but most scientists concluded they had landed on barren soil.

Since the Viking mission, NASA has followed a more progressive approach focused on finding and exploring sites that show evidence of being potentially habitable billions of years ago, when Mars was warmer and wetter. Perseverance and its still-active predecessor, the Curiosity rover, have found traces of organic molecules, the kind of molecules that underlie life as we know it, on the surface, though this is not in itself proof of an origin. biological.

“The question remains whether they are meteorites, geological or biological,” said Amy Williams, a planetary scientist at the University of Florida and a member of the Curiosity and Perseverance science teams.

Williams said the new report by Azua-Bustos and her colleagues is important because it shows that the preservation of organic matter is limited in Mars-like environments and will be difficult to detect even with state-of-the-art laboratory instruments.

“This means that detection of organic compounds with spaceflight instruments, such as on current and future Mars rovers, may be even more challenging, as organic matter readily decays in the moon-drenched Martian surface environment. radiation,” Williams said in an email.

Still, the Atacama research shows that even a very arid environment will have layers of sedimentary rock with significant amounts of biological remains, said Chris House, a geologist and astrobiologist at Pennsylvania State University. “It’s not really a surprise, but the results could have shown consistent bleeding,” he said. That’s good news for scientists who hope dry rocks on Mars could yield traces of alien biology.

Azua-Bustos is an Atacama native who spent years as a winemaker before becoming a scientist. He remembers growing up in a Chilean town where rain fell only once a year, always a highlight. There are places, he said, where residents have never seen rain for generations.

He said he would regularly pass through a desert region, called Red Stone, on his way to a research site, and one day he decided it might be worth taking a closer look. The rocks were rusty red due to the presence of a mineral, hematite, which also explains the red color of Mars, he said.

More than 100 million years ago, in the age of the dinosaurs, the Red Stone site was a river delta, much like the plateau on Mars inside the Jezero crater that Perseverance is exploring.

Azua-Bustos was surprised by the genetic material of an unknown nature seen in the Atacama investigation. All life on earth stems from a common ancestor, as far as we know. There has been speculation, notably by scientist and author Paul Davies, that life could have originated on Earth more than once and to this day there could be a “shadow” biosphere that is simply too weird to fit into. our definition of life on Earth.

Azua-Bustos, however, resorts to the less spectacular interpretation of unclassified organisms: they are relict genetic material from previously undocumented and long-extinct life forms.

The Perseverance rover continues to explore Jezero Crater, excavating and storing samples of Martian soil. The plan is to put another spacecraft on the surface, which would also function as a launch pad. Perseverance would then deliver the samples to the lander, which would launch the material into orbit. There it would meet another vehicle, a European-built orbiter, which could carry the precious cargo back to Earth. for analysis with the best possible laboratory instruments.

New research suggests this may be the most effective method – and possibly the only conclusive way – to find out if anything was ever alive on Mars.

“We know there are things to detect,” Azua-Bustos said. “But if your instrument is not designed to be able to detect those things, then we have a problem.”

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