A call to caution for exoplanet hunters

Behind the excitement generated by the acceleration of exoplanet discoveries, there is an important drawback: the details that we think we will discover on one or another of these planets orbiting distant stars come with a large margin of uncertainty.

An exoplanet previously thought to have an ocean has now been revealed to be a gas planet.

K2-18b – that's its name – orbits a star located 110 light-years away. Since its discovery in 2015, the planet has stood out: It was in the category of so-called “super-Earths” or “mini-Neptunes,” which refers to rocky planets, not giant gas balls like Jupiter, Saturn, Uranus, or Uranus. Neptune.

In 2019, astronomers detected traces of water vapor there, and this planet is also located In what astronomers call the “habitable zone.” », So it is at the right distance from its star for this water to exist there in a liquid state: a condition for life. The most optimistic, given the size of the planet, started talking about the ocean. Finally, in 2023, We found out In the atmosphere, thanks to the James Webb Space Telescope (JWST), traces Dimethyl sulfide: A molecule that only living organisms, including plankton, produce on Earth.

However, a new analysis of James Webb Space Telescope data suggests that the abundance of methane and carbon dioxide points more towards a planet that might be a ball of gas, rather than a rocky planet largely covered by an ocean – the reason being explained – is that this would be broken up. Molecules through a process called photolysis if they are swimming in the ocean world. As for dimethyl sulfide, it is a “false signal.”

New search It has only been previously published so far (currently being reviewed for publication in the journal). Astrophysical Journal Letters). But this research It is above all a reminder Because the data that astronomers have been able to extract from observations of the James Webb Space Telescope, despite the unprecedented power of this telescope, It remains very partial. And This research is also a reminder Any confirmation of the discovery of a “biosignature” – an atmospheric “fingerprint” that can be attributed to life – should be treated with the utmost caution, as long as it is not confirmed and reconfirmed by other analyses. .

Subscribe to our sprawling newsletter