Researchers found evidence of microbial life in what should have been a pristine sample of an asteroid, a frustrating sign that avoiding earthly contamination may be harder than we thought.
A team from Imperial College London discovered a population of microorganisms in samples of the asteroid Ryugu, which were retrieved by Japan’s Hayabusa2 mission in 2019. The microbial life turned out to have terrestrial origins, indicating that the asteroid sample was contaminated during its time on our planet. The findings are detailed in a study published in Meteoritics and Planetary Science.
Usually, studies of space rocks involve meteorites, which have plunged through Earth’s atmosphere and hit the ground. Those samples can tell us a lot about the composition of objects in space, but by the time scientists study them, they’ve been thoroughly contaminated by the environment of Earth. But two recent missions—Japan’s Hayabusa2 and NASA’s OSIRIS-REx—collected bits of asteroid directly from outer space. Those samples were brought to Earth and intensely protected, in the hopes that researchers would have a chance to study material unaffected by our atmosphere and microbial life.
The Japanese space agency (JAXA)’s Hayabusa2 collected 5.4 grams (about a teaspoon’s worth) of rock, pebbles, and dust from the Ryugu asteroid when it was nearly 200 million miles from Earth. The spacecraft dropped off the samples in 2020, which were sealed within a capsule that made a soft landing at the Woomera Range Complex in the South Australian outback.
The capsule was then transported to a facility in Sagamihara, Japan, built especially to accommodate the asteroid samples. It was first opened inside a vacuum room, located inside a clean room, and later sent to a pressurized room with a constant flow of nitrogen meant to keep out Earthly contaminants. Bits of the sample were then placed inside nitrogen-filled containers and sent out to researchers around the world for analysis.
The team behind the recent discovery received their own piece of Ryugu. After scanning the asteroid sample, they found rods and filaments of organic matter, which were interpreted as thin, thread-like microorganisms. The microbial community originated through terrestrial contamination and did not have extraterrestrial origins, the researchers determined. The discovery suggests that the strict protocols in place to avoid bacterial contamination just weren’t good enough.
In 2020, a NASA spacecraft retrieved samples from the asteroid Bennu and dropped them off on Earth in 2023. The space agency followed similar protocols to JAXA to protect the asteroid material, and no Earthly bacteria has been reported on the bits of Bennu yet.
Ryugu is a carbonaceous asteroid, a group thought to be the rocky building blocks of the solar system. By analyzing these asteroids in a lab, scientists might better understand how the solar system formed and how life later emerged on Earth. An earlier analysis of Ryugu samples found organic molecules on the space rock, suggesting that the ingredients for life came to Earth by way of meteorite and asteroid impacts.
Sample return missions can provide unprecedented access and insight to nature of our solar system, but keeping that material pure is proving to be more challenging than initially believed.
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