According to news on November 28, scientists discovered that the samples collected by the Japanese probe from the Ryugu asteroid (Ryugu) had been "occupied" by Earth's microorganisms after being returned to Earth. This research shows that not only microorganisms on the earth have tenacious vitality, but also extraterrestrial materials are not a problem.
The samples were collected by the Japan Aerospace Exploration Agency's (JAXA) Hayabusa2 probe. Hayabusa2 was launched in December 2014, arrived at Ryugu in June 2018, and spent a year conducting detailed research on the asteroid, which is about 900 meters in diameter. Subsequently, the detector landed on the surface of Ryugu and successfully collected samples. These samples were returned to Earth on December 6, 2020, while Hayabusa2 continues to fly into deep space to explore other asteroids.
Ryugu samples were distributed to multiple scientific research teams, including the team that discovered Earth's microorganisms this time.
Matthew Genge, leader of the research team at Imperial College London, said: "We found microorganisms in the samples returned from the asteroid. They first appeared on the rock surface, then spread and finally disappeared." "The change in the number of microorganisms indicates that they are living organisms, and that they began to colonize the sample shortly before the sample was analyzed, and that they originated from Earth."
The team found rod-shaped and thread-like organic matter in the samples, which they interpreted as filamentous microorganisms. Although the exact types of these microorganisms cannot yet be determined, Genge has reasonable speculations about their identities.
"You can't pinpoint their species without studying their DNA," Genge said. "However, they are most likely bacteria such as Bacillus, as these are very common filamentous microorganisms found particularly in soil and rocks."
Of course, given humanity's current efforts to search for microbial life beyond Earth, particularly on Mars, one question is: Could these microbes have been present on Ryugu at the time the samples were collected, and thus represent extraterrestrial life? But the research team specifically ruled out this possibility.
"We examined the samples using nano-X-ray tomography before analyzing them and did not find any microorganisms," Genge said. "In addition, changes in the number of microorganisms indicate that they appeared after the samples were exposed to the Earth's atmosphere, more than a year after the samples were returned to Earth."
The study found that 11 microorganisms appeared on the surface of the sample after being exposed to the Earth's atmosphere for a week; after another week, the number grew to 147.
Genge said: "It is very surprising to find Earth microorganisms in sample rocks. We usually polish meteorite samples, so we rarely see microorganisms attached. But only one microbial spore is enough for them to multiply rapidly."
While the study doesn't provide direct clues about extraterrestrial life, it reveals the tenacity of Earth's microbes, especially when it comes to adapting and reproducing. The findings have also sparked discussion about the possible contamination of the environments of target planets or asteroids by spacecraft and probes.
Genge said: "Research shows that microorganisms can quickly metabolize and survive on extraterrestrial materials. There are abundant indigenous organic matter on the earth for microorganisms to use, and on extraterrestrial planets such as Mars, extraterrestrial organic matter may even support an ecosystem."
He further pointed out: "Our findings indicate that space missions may be contaminating extraterrestrial environments and also show the rapid colonization ability of Earth's microorganisms."
Fortunately, space agencies of various countries have adopted strict planetary protection measures to minimize the risk of contamination. However, Genge reminded that when samples are sent back to Earth in the future, scientists need to pay special attention to avoid contamination by Earth's microorganisms to avoid being misjudged as evidence of extraterrestrial life.
He said: "Earth's microorganisms are among the most powerful colonizers of the planet. While contamination is not a problem in most cases as long as the source of the contamination is known, it becomes a big problem if scientists claim that the 'pristine' characteristics of the sample prove that it is evidence of extraterrestrial life."
The Imperial College London team is continuing to study samples from the Ryugu and Bennu asteroids. "Hopefully, the next time the samples are studied, there will be no microbial 'visitors' from Earth," Genge said.
The research results have been published in the journal Meteoritics & Planetary Science.