The analysis of a sample from the asteroid Ryugu, brought back by the Hayabusa2 mission, reveals the presence of microorganisms. Unfortunately, this is not evidence of extraterrestrial life, but of spectacular terrestrial contamination, highlighting the remarkable adaptability of life on Earth. This discovery has major implications for space exploration missions.
A promising initial discovery
Space exploration, the incessant quest for answers to the mysteries of the universe, carries with it the ultimate hope of discovering forms of extraterrestrial life. The analysis of asteroid samples, real time capsules testifying to the formation of the solar system, represents a crucial step in this research. However, a recent study on a sample from the asteroid Ryugu, brought back to Earth by the Hayabusa2 mission of the Japanese space agency (JAXA), tempers this enthusiasm. If living organisms have indeed been discovered, it turns out that they are not extraterrestrial life forms, but unexpected terrestrial contamination. This spectacular contamination highlights the tremendous capacity for adaptation and colonization of life on our planet, even in extreme conditions.
Sample A0180, a tiny particle of regolith (surface material) measuring 1 x 0.8 mm taken from Ryugu, was subjected to extensive analysis for more than two years. Initially transported and stored under draconian aseptic conditions, the sample was then manipulated for the preparation of polished blocks intended for observation under a scanning electron microscope (SEM). It was during these observations that the discovery was made: filaments and sticks of organic matter, whose size and morphology are strongly reminiscent of filamentous microorganisms, were revealed on the surface of the sample. .
The research team, led by Matthew Genge of Imperial College London
initially considered the possibility of an extraterrestrial life form. The presence of cell-like structures, associated with organic matter from the asteroid, indeed seemed promising. However, further analysis revealed significant variations in the abundance of these filaments over time.
The turning point: the temporal evolution of the microbial population
The number of microorganisms experienced a dramatic increase (from 11 to 147 individuals in just a few days), followed by a gradual decrease. This cycle of growth and decline, characteristic of a microbial population, was decisive in the researchers' conclusion. Coupled with the absence of detectable microorganisms before sample preparation, this observation made it possible to definitively rule out the hypothesis of indigenous extraterrestrial life. The growth observed occurred after arrival on Earth, confirming contamination of terrestrial origin.
The estimated generation time for these organisms (approximately 5.2 days) is consistent with that of certain bacteria, notably Bacillus. Although a precise identification of the species was not possible in the absence of DNA analysis, the hypothesis of contamination by bacteria of the Bacillus genus, very widespread in soil and rocks, appears the most plausible. .
Terrestrial contamination: an inevitable scenario?
The contamination appears to have occurred during the sample preparation phase, despite JAXA's extremely rigorous sterilization protocol. Exposure of the sample to the Earth's atmosphere, even for a short period, was sufficient to allow colonization by one or more spores. This discovery highlights the fragility of extraterrestrial samples and highlights the need to implement even stricter contamination protocols for future sample return missions. Even with exceptional precautions, it appeared that terrestrial life is particularly good at colonization.
This discovery, while disappointing with respect to the search for extraterrestrial life on Ryugu, has far-reaching implications for astrobiology and space missions. It highlights the exceptional resistance and colonization capacity of terrestrial microorganisms, capable of thriving in apparently unfavorable conditions. It also raises critical questions regarding the contamination of extraterrestrial environments by space missions themselves, highlighting the need to significantly improve planetary protection protocols.
The study of the Ryugu sample demonstrated that the organic matter present in meteorites, even in an extreme environment, can serve as a support for the development of life. This observation has direct consequences for the interpretation of data collected on other celestial bodies, and in particular for the analysis of the presence of organic matter on Mars.
Towards strengthened planetary protection protocols
The case of Ryugu, despite the lack of confirmation of extraterrestrial life, constitutes a valuable warning for the scientific community. It highlights the challenges inherent in the search for life beyond Earth and emphasizes the need for extreme rigor in preventing terrestrial contamination. The search for extraterrestrial life is a complex undertaking that requires constant vigilance and perpetual questioning of assumptions. Future sample return missions will have to integrate the lessons learned from this experience to avoid contamination and optimize the chances of detecting, one day, tangible proof of life elsewhere in the universe.
The future of space exploration lies in the constant improvement of planetary protection protocols, in order to guarantee the scientific integrity of extraterrestrial samples and to preserve the possibility of discovering, with certainty, traces of life beyond our own. planet. The race to discover extraterrestrial life is far from over, and the Ryugu experiment reminds us that scientific rigor and caution remain our best allies in this fascinating quest.
