Solvent extractions of the Ryugu samples on a clean bench (ISO6, Class 100) inside a clean room (ISO5, Class 1000) performed by Hiroshi Naraoka at Kyushu University in Japan. (JAXA/NASA)
When scientists discovered water and a chemical compound common in RNA on a rock from the asteroid Ryugu, astronomy fans and laypeople alike held their collective breath for the chance of extraterrestrial life. As more evidence of microorganisms emerged, experts began to wonder if humans would soon learn life exists somewhere in the universe besides Earth.
A recent study in the journal Meteoritics and Planetary Science threw cold water on the idea -- the microbes on Ryugu almost certainly came from Earth rather than outer space. They learned this because a sample from Ryugu, retrieved by the Hayabusa 2 mission 186 million miles from Earth, sent to Matthew Genge at Imperial College London was thoroughly tested for evidence of microbial life. None were found, indicating that the organic chemicals initially discovered were Earthly contaminants rather than indigenous to Ryugu.
"The presence of terrestrial microorganism within a sample of Ryugu underlines that microorganisms are the world's greatest colonizers and adept at circumventing contamination controls," the authors conclude. "The presence of microorganisms within space-returned samples, even those subject to stringent contamination controls is, therefore, not necessarily evidence of an extraterrestrial origin."
This is not the first time that scientists received false hope about proof of extraterrestrial microorganic life. In 2020 researchers publishing in the journal Nature Astronomy revealed that the atmosphere of Venus appeared to contain trace amounts of phosphine, a gas associated with anaerobic bacteria on Earth. Yet two subsequent scientific investigations failed to replicate the earlier study's results, suggesting that there was no phosphine as previously thought.
On that occasion, the scientific error was that analysts misread the results from spectrometric readings of the Venusian atmosphere. This time the issue was much simpler -- as the authors themselves wrote, "the discovery emphasizes that terrestrial biota can rapidly colonize extraterrestrial specimens even given contamination control precautions."