They question the discovery of water vapor on an exoplanet

New calculations show that the gas in the atmosphere of K2-18 b may be methane and not water , as indicated in a 2019 study.


The discovery of water in the atmosphere of a potentially habitable exoplanet  , announced in 2019, has been called into question in a new study, its author said on Monday.

“It is possible that there is water vapor around K2-18 b , but at the moment we are not sure,” said astrophysicist Bruno Bézard of the Paris-PSL Observatory.

Calculations made with the data from that time conclude that methane and not water was detected , according to the study published Thursday in Nature Astronomy . Despite this, 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 from the solar system.

The 2019 announcement shook the world of planetologists because it was the first, and so far only, exoplanet located in the so-called “habitable zone”, meaning that, like Earth, it is neither too close nor too far from its star. for water to exist in a liquid state and life to be possible.

With a mass eight times that of Earth, K2-18 b is described as a “super-Earth” or “mini-Neptune”.

New calculations

The 2019 study used observations from the Hubble Space Telescope to analyze light filtered through the planet’s atmosphere. The results revealed the molecular signature of water vapor, the authors said at the time.

The team of scientists from the Paris Observatory and the German Max Planck Institute has now taken up these data. Although they do not dispute the possibility of detecting the presence of water, they state that the signals recorded “could perfectly be due to methane,” according to Bézard.

In particular, they question the fact that the 2019 study ruled out any scenario in which the atmosphere contains methane, a gas made up of carbon and hydrogen.

“It is not clear why they favored the models in which there is no methane,” says the scientist.

The James Webb Space Telescope (JWST), launched a few months ago and much more powerful than Hubble, could help clarify the issue .

According to Bézard, an observation time of the atmosphere of K2-18 b is already planned . “With this, we will be able to determine if there is indeed water vapor and in what proportion”, he concludes.