Strange DNA found in desert offers lessons in the hunt for Martian life


The Atacama Desert is about the driest place on earth. In spots it looks a lot like Mars. But it is not lifeless, even in the hyperarid regions. Using state-of-the-art equipment to examine the desert rocks, the researchers found bits of DNA from a fascinating mixture of microbes.

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

These organisms are bacteria that are “so strange and different,” as the report says, that scientists could not identify any known relatives.

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

And that brings him back to the Mars analogy: Atacama, he and his scientific colleagues 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 the microbial signatures. That means it will be difficult to find conclusive evidence of current or past life in Martian soil without bringing samples back to Earth, Azua-Bustos and his colleagues concluded.

The research appears to strengthen 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 as planned, samples of Martian soil obtained by NASA’s Perseverance rover — which just celebrated its second anniversary on Mars — will be returned to Earth sometime early next decade for scrutiny in high-containment laboratories.

But this new research also highlights the challenges facing scientists who want to know the (hypothesized) biological history of Mars. Microbial life, especially if it is extinct and long fossilized, may exist at or beyond the very limit of what can be detected with the kinds of instruments small enough to be blasted 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 will emerge, somehow, under the right conditions. The red planet has long tempted astrobiologists. It was more Earth-like about 3 billion years ago, when it had a thicker atmosphere and liquid water on its surface. There is possibly still cryptic life on Mars, although astrobiologists would be thrilled to find even a microfossil of something that lived billions of years ago.

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

Since the Viking mission, NASA has pursued a more incremental strategy focused on finding and exploring sites that show evidence of being potentially habitable billions of years ago, when Mars was warmer and wetter. Endurance and its still active predecessor, the Curiosity rover, have found traces of organic molecules – the kind of molecules that are the basis of life as we know it – on the surface, although this is not in itself evidence of a biological origin.

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

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

“This means that detection of organics by spacecraft instruments, such as on current and future Mars rovers, may be an even greater challenge, as organic matter readily degrades in the radiation-bathed surface environment of Mars,” Williams said in an email.

Still, the Atacama research shows that even a very dry environment would have layers of sedimentary rock with significant amounts of biological remains, said Chris House, a geologist and astrobiologist at Penn State. “It’s not really a surprise, but the results might just have shown uniform gloom,” he said. That’s good news for scientists who hope dry Martian rocks may yield traces of alien biology.

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

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

More than 100 million years ago, during the age of the dinosaurs, the Red Stone area was a river delta, much like the Martian plateau within the Jezero crater Perseverance explores.

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

However, Azua-Bustos defaults to the less spectacular interpretation of the unclassified organisms: This is genetic material from life forms that have long been extinct and not previously documented.

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 will act as a launch pad. Endurance would then deliver the samples to the lander, which would eject the material into orbit. There it would rendezvous with yet another vehicle, a European-built orbiter, which could carry the precious cargo back to Earth for analysis with the best possible laboratory instruments.

The new research suggests that this may be the most effective – and possibly the only definitive – way to find out if anything has ever been alive on Mars.

“We know there are things to discover,” Azua-Bustos said. “But if your instrument isn’t designed to be able to detect these things, then we have a problem.”

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