Samples of 'alien' asteroid Ryugu are crawling with life — from Earth

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Scientists have found microorganisms crawling over a sample retrieved from the 200 million-mile-distant asteroid Ryugu. But they almost certainly came from Earth.

microscopic image of of the Hayabusa2 samples returned from C-type asteroid Ryugu
The sample gathered from the asteroid Ryugu by the Hayabusa2 spacecraft. (Image credit: Yada, et al.; Nature Astronomy)

A rock retrieved from a near-Earth asteroid is crawling with microbial life, scientists have discovered. But the bacteria on its surface almost certainly came from Earth.

The sample is part of a 0.2-ounce (5.4 grams) chunk of rock that Japan's Hayabusa2 spacecraft scraped from the surface of the asteroid Ryugu and brought back to our planet in 2020.

But it seems that somewhere along the way, for one sample of this rock, these preventative measures were not enough. The scientists behind a new study found that one sample, which was embedded in a resin at Imperial College London in the U.K., had filamentous microorganisms, closely matching terrestrial prokaryotic bacteria, crisscrossing its surface. They published their findings Nov. 13 in the journal Meteorics and Planetary Science.

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"The presence of microorganisms within meteorites has been used as evidence for extraterrestrial life, however, the potential for terrestrial contamination makes their interpretation highly controversial," the researchers wrote in the study. "The discovery emphasizes that terrestrial biota can rapidly colonize extraterrestrial specimens even given contamination control precautions."

Scientists have long debated whether the blueprints for life on our planet originated here or came from the heavens. Previous analyses of meteorites found on Earth have revealed that some of these space rocks contain the five nucleobases essential for organic life.

An animation of asteroid Ryugu made with images from JAXA's Hayabusa2 mission.

A view of the C-type asteroid 162173 Ryugu, seen by the ONC-T camera on board of Hayabusa2. (Image credit: JAXA/University of Tokyo/Kochi University/Rikkyo University/Nagoya University/Chiba Institute of Technology/Meiji University/University of Aizu/AIST)

But whether the compounds came from space aboard the rocks or contaminated the meteorites after their arrival on Earth has long been an open question. The Hayabusa2 mission was one attempt to address this, and with some success — parts of its sample contained amino acids and even the nucleobase uracil.

After receiving their sample, which was shipped from Japan to the U.K. inside its container, the researchers scanned the space rock using X-rays and found no signs of bacteria on its surface. Then, after three weeks, they moved the sample into a resin, studying it more closely after a subsequent week using a scanning electron microscope (SEM).

Surprisingly, their results revealed rods and filaments of organic matter teeming over the sample's surface.

Yet to the researchers' disappointment, the growth rates, shapes and sudden appearance of the bacteria all matched closely with microbes found on Earth, suggesting that the sample became contaminated sometime after being placed inside the resin.

This means the chunk of asteroid is unlikely to reveal any unambiguous insights into the contents of Ryugu's surface, but it doesn't mean it has nothing to teach us. Beyond flagging the importance of extremely stringent decontamination procedures for samples retrieved from space, the researchers said their study also highlights the incredible adaptability of microbes — which rapidly consume organic material from anywhere, no matter the planet.

"The presence of terrestrial microorganism[s] within a sample of Ryugu underlines that microorganisms are the world's greatest colonizers and adept at circumventing contamination controls," they wrote. "The presence of microorganisms within space-returned samples, even those subject to stringent contamination controls, is, therefore, not necessarily evidence of an extraterrestrial origin."

Ben Turner
Ben Turner
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Ben Turner is a U.K. based writer and editor at Live Science. He covers physics and astronomy, tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.