Researchers found that a sample of the asteroid Ryugu was rapidly colonized by terrestrial microorganisms, even under strict contamination control measures.

To ensure minimal contamination, the sample was transported to Earth in a hermetically sealed chamber and opened in a nitrogen-filled class 10,000 clean room. Each particle was carefully handled with sterilized tools and stored in airtight containers under nitrogen. Prior to analysis, the sample underwent Nano-X-ray computed tomography and was embedded in an epoxy resin block for further investigation using scanning electron microscopy.

Organic rods and filaments, interpreted as filamentous microorganisms, were identified on the surface of the Ryugu sample. These structures displayed variations in size and morphology that closely resembled known terrestrial microbes. Interestingly, their abundance fluctuated over time, suggesting the growth and decline of a prokaryotic population with an estimated generation time of 5.2 days.

Population analysis revealed that these microorganisms likely resulted from terrestrial contamination during the sample preparation process, rather than being native to the asteroid. This finding underscores the challenges of distinguishing between Earth-based contaminants and potential extraterrestrial life forms in such studies.