Ryugu asteroid sample rapidly colonized by terrestrial life despite strict contamination control

Panspermia is the hypothesis that life can survive the transfer between planetary bodies as a secondary path for life to get started on planets throughout a solar system. The discovery of extraterrestrial life on asteroids or within meteorites would have profound implications for understanding the origins and distribution of life in the universe.

Reports of microorganisms found in chondritic meteorites have long fueled debates about extraterrestrial life reaching Earth and possibly as an origin of life here. While studies have concluded these microbial signatures are just terrestrial contaminants, arguments for them being extraterrestrial travelers have continued.

Researchers from Imperial College London have discovered that a space-returned sample from asteroid Ryugu was rapidly colonized by terrestrial microorganisms, even under stringent contamination control measures.

In the study, “Rapid colonization of a space-returned Ryugu sample by terrestrial microorganisms,” published in the journal Meteoritics & Planetary Science, researchers analyzed sample A0180, a tiny (1 × 0.8 mm) particle collected by the JAXA Hayabusa 2 mission from asteroid 162173 Ryugu.

Transported to Earth in a hermetically sealed chamber, the sample was opened in nitrogen in a class 10,000 clean room to prevent contamination. Individual particles were picked with sterilized tools and stored under nitrogen in airtight containers. Before analysis, the sample underwent Nano-X-ray computed tomography and was embedded in an epoxy resin block for scanning electron microscopy.

Rods and filaments of organic matter, interpreted as filamentous microorganisms, were observed on the sample’s surface. Variations in size and morphology of these structures resembled known terrestrial microbes. Observations showed that the abundance of these filaments changed over time, suggesting the growth and decline of a prokaryote population with a generation time of 5.2 days.

Population statistics indicate that the microorganisms originated from terrestrial contamination during the sample preparation stage rather than being indigenous to the asteroid.

Results of the study determined that terrestrial biota had rapidly colonized the extraterrestrial material, even under strict contamination control. Researchers recommend enhanced contamination control procedures for future sample-return missions to prevent microbial colonization and ensure the integrity of extraterrestrial samples.

Another factor in gathering contamination-free sampling is that everything used to collect extraterrestrial material originates on a planet awash in microbial life.

NASA tries to avoid introducing Earth microbes to Mars by constructing probes and landers in cleanroom environments and has found the task nearly impossible. There have been species of microbes discovered in NASA clean rooms that not only evade disinfection methods but also adapt to using cleaning agents as a food source.

Microbial life on Earth is so abundant that no resource is left unexploited, and no niche left unoccupied. It is one of the reasons that all life on the planet is related through evolution, traced back to a common origin rather than having started from scratch many times.

Genomic evidence shows this to be the case. The reason there have not been new forms of life originating on Earth, evolving alongside our microbial cousins, could be that there is simply no room for a newcomer. In a system where every niche is filled with more advanced life looking for a next meal, even if a new form of life got started, it would not last long.

There is still hope for the panspermia hypothesis in the current study as it has reinforced a few key concepts. It demonstrates that extraterrestrial organic material can provide a suitable source of metabolic energy for organisms originating on Earth, showing that the microbes do not have a strict planetary preference.

It also shows that even our best efforts to create a clean room environment are not enough to prevent life from finding a way in, something that has likely already introduced extraterrestrial Earth microbes to the moon and Mars.

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