A new study calls into question the discovery of water in the atmosphere of the potentially habitable exoplanet K2-18b.
The discovery of water in the atmosphere of a potentially habitable exoplanet, announced with fanfare in 2019, is called into question in a new study, its author explained on Monday. “There may be water vapor around K2-18 b, but for the moment we are not sure,” astrophysicist Bruno Bézard, from the Observatory of Paris, told AFP. Paris-PSL.
Calculations carried out using data from the time conclude that methane has been detected rather than water, according to the study published Thursday in Nature Astronomy. Even if, moreover, the scientist wants to believe that “there is not only methane but also water vapor” in the atmosphere of the planet, located in the constellation of Leo 110 light years away. of the solar system.
The announcement of 2019 had shaken the world of planetologists, because it concerned the first, -and until today the only-, exoplanet located in the so-called “habitable” zone of its solar system. That is to say, a star found, like the Earth, at a distance neither too close nor too far from its star to make life possible there. With a mass equal to eight times that of our planet, K2-18 b is qualified as “super-Earth” or “mini-Neptune”. The 2019 study used observations made by the Hubble Space Telescope to analyze the light filtered by the planet’s atmosphere. According to them, their results revealed the molecular signature of water vapour.
No traces of methane
The team of scientists from the Paris Observatory and the German Max Planck Institute took over this data. She does not dispute the possibility of detecting the presence of water there, but affirms that the signals recorded “may very well be due to methane”, according to Mr. Bézard.
He questions in particular the fact that the 2019 study ruled out any scenario in which the atmosphere would contain methane, a gas composed of carbon and hydrogen. “We don’t see why they favored models where there is no methane,” he says.
The justice of the peace responsible for deciding the case is already at his post: the James Webb Space Telescope (JWST), much more efficient than Hubble, which will soon enter service. Observation time of the atmosphere of K2-18 by is already scheduled, according to Mr. Bézard. “With that, we can determine if there is indeed water vapor and in what proportion,” he concludes.