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Are we alone in the universe? The cult series X-Files said it: ” The truth is elsewhere ». What if it was 124 light years from the earth? An international team of astronomers claims to have detected the most convincing signals to date of a possible biological activity beyond our solar system. Their observations of the K2-18B exoplanet, in the lion constellation, reveal the presence of molecules that are associated, on earth, with living processes. An intriguing discovery, still debated, but which could mark a major advance in the search for an extraterrestrial life.
K2-18B, detected in 2015, intrigues researchers by its unusual characteristics. Classified among the “super-terres”, this exoplanet has a mass about nine times that of the earth and displays a diameter 2.6 times larger. It revolves in the so -called “habitable” area of its star – a red dwarf, colder and smaller than our sun -, completing an orbit in 33 terrestrial days. Its surface temperature, depending on the estimates, could be comparable to that of the earth.
The research was led by Professor Nikku Madhusudhan, astrophysicist at the University of Cambridge. In 2019, data from the Hubble space telescope had already revealed traces of water vapor in the atmosphere of K2-18B. Some scientists had then mentioned the possibility of a world covered with oceans, under an envelope rich in hydrogen.
« This is the most robust proof of a biological activity outside the solar system ever obtained to this day “Said Professor Madhusudhan at a press conference held on March 15. In 2023, thanks to the infrared instrumentation of the James Webb space telescope (JWST), his team highlighted a marked signal corresponding to the potential presence of dimethyle sulfide (DMS) and Dimethyle disulfide (DMDS) – two compounds produced, on our planet, by living organizations, mainly phytoplancon marine in the case of DMS. The biological role of DMDS, more rare, remains less clearly established.
« Here we hold independent proof, obtained using a separate instrument, on a different range of wavelengths, without cross -checking with the previous data “Said the researcher in a press release. “” The signal was strong, although the level of statistical meaning remains below the required threshold for formal validation “, He added.
A still insufficient service threshold
These results, published in the journal The Astrophysical Journal
Lettersindicate a level of statistical significance of three sigma: in other words, a probability of 0.3 % that observation is the fruit of chance. However, the scientific community only grants a discovery from a threshold of five sigma – an in 3.5 million chance to be wrong.
The team estimates that between 16 and 24 hours of additional JWST observations could make it possible to reach this threshold. But the constraints linked to the observation of the atmosphere of an exoplanet make this scenario still hypothetical.
Several voices, however, rise to call for caution. “”
These new JWST data do not allow to assert the presence of DMS or DMDS in the atmosphere of K2-18B “, Temperates Ryan Macdonald, of the University of Michigan, quoted by the New Scientist. “” We are in a situation close to that of the boy who shouted in the wolf: several sigma three detections on K2-18B have already proven unfounded after verification “, He recalls.
The very nature of this planet remains subject to debate. While the Cambridge team favors the hypothesis of an ocean world, other scientists do not exclude that it is a sparkling giant, or a star covered with Magma oceans.
According to Madhusudhan, the estimated concentrations of DMS and DMDS would exceed 10 parties per million, a rate which, if confirmed, would indicate a more intense biological activity than that observed on earth.
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« Caution remains “, Enterests, however, the researcher. “” At this stage, we cannot say that the detection of these molecules is a biological activity. But in the light of current knowledge, no abiotic process seems to be able to explain such a signal He adds.
For Nicholas Wogan, from the NASA Ames Research Center, reading JWST data remains a complex exercise. “” It is not just a question of downloading a file to seek the signature of the DMS. The interpretation of these data is extremely demanding “, He warn.
At a distance from 124 light years, any direct observation prospect remains out of reach. Madhusudhan compared this situation to other major scientific advances: ”
In astronomy, it is not a question of going physically on site. The challenge is to determine whether the laws of biology are universal. Just because you can see a fish that you have to dive into the water to fish “He told the Guardian.
