The Invaders

In December 2020, Japan’s Hayabusa2 mission successfully returned samples from the asteroid Ryugu, delivering them to Earth in a sealed capsule. The pristine material was then distributed to scientists globally to unlock the secrets of the early solar system.

As researcher Matthew Genge and his team at Imperial College London began to analyze the material in 2022, they noticed something unusual while studying one of the Ryugu grains: Tiny rod-shaped filaments appeared on the rock’s surface, increasing in number with time.

“We found micro-organisms in a sample returned from an asteroid,” Genge recently told Space.com. ‘They appeared on the rock and spread with time before finally dying off.”

Initially, the discovery raised tantalizing questions about extraterrestrial life, such as whether these microbes have originated from the space rock.

Their new study, however, dashed those hopes. The rapid growth of the filaments strongly suggested terrestrial origins.

Genge explained that “the change in population suggests they only appeared after the rock was exposed to the atmosphere, more than a year after it was returned to Earth.”.

The contamination likely occurred during sample preparation at the Natural History Museum in London, where the grain was polished for study.

Despite meticulous protocols, Genge admitted to Scientific American that “you only need one bacterial cell to fall on your specimen – and that’s it, it’s contaminated.”

The microbes were likely Bacillus bacteria, known for their resilience and ability to thrive in extreme environments.

While the study may disappoint those hoping to find evidence of extraterrestrial life, it reveals an interesting silver lining – and a cautionary tale – about Earth’s lifeforms, according to Genge.

“It shows that microorganisms can readily metabolize and survive upon extraterrestrial materials,” Genge told Space.com. “Our findings suggest that space missions could be contaminating space environments. It also shows that terrestrial microorganisms are adept at rapid colonization.”

Andrew Steele, an astrobiologist at Carnegie Science who was not involved in the study, said the episode illustrates the challenges of working with extraterrestrial samples.

“Ultimately, we do live on a planet that is ruled by microbes, and chance events do happen,” he told Scientific American.