Japan brought rocks from asteroid Ryugu. Earth-based bacteria colonised it

The samples were collected by Japan's Hayabusa-2 spacecraft, which launched in December 2014 and successfully rendezvoused with Ryugu in June 2018.

In Short

• The team observed filamentous structures
• They likely belonged to common bacterial groups such as Bacillus
• These microbes could represent extraterrestrial life

Scientists have made a surprising discovery involving a sample from the asteroid Ryugu, which was found to be overrun with Earth-based microorganisms after its return to our planet.

This research highlights the remarkable ability of terrestrial microbes to colonise extraterrestrial materials, raising questions about contamination and the potential for life beyond Earth.

The samples were collected by Japan’s Hayabusa-2 spacecraft, which launched in December 2014 and successfully rendezvoused with Ryugu in June 2018.

After spending a year studying the asteroid, approximately 3,000 feet (900 meters) in diameter, Hayabusa-2 scooped up a sample that was returned to Earth on December 6, 2020. The sample was subsequently divided among various research teams for analysis.

Matthew Genge, team leader and palaeontologist at Imperial College London, stated, “We found micro-organisms in a sample returned from an asteroid. They appeared on the rock and spread with time before finally dying off.”

The team observed filamentous structures that they interpreted as microorganisms, likely belonging to common bacterial groups such as Bacillus, although their precise identification remains uncertain without DNA analysis.

Despite initial hopes that these microbes could represent extraterrestrial life, the researchers ruled this out.

Genge explained that no microbes were detected during initial scans of the sample before it was exposed to Earth's atmosphere. Within just a week of exposure, microbial life began to flourish on the specimen’s surface, indicating that these organisms colonised the sample after its return to Earth.

The findings show the adaptability of Earth’s microorganisms and raise concerns about contamination during space missions.

Genge cautioned that while space agencies implement stringent planetary protection measures, the presence of terrestrial microbes can complicate the search for extraterrestrial life.

“The fact that terrestrial microbes are the Earth's best colonizers means we can never completely discount terrestrial contamination,” he noted.

As scientists continue to study samples from Ryugu and other asteroids like Bennu, they aim to refine their methods for preventing contamination and ensuring the integrity of future extraterrestrial materials.

The research was published in the journal Meteoritics & Planetary Science.