James Webb may have detected water vapor in rocky planet's atmosphere
The James Webb Space Telescope (JWST) has detected water vapor near a planet in another system, which could mark the first direct detection of a rocky exoplanet’s atmosphere. But there’s a big if hanging over the find.
Whether there’s life on other planets is one of the most profound scientific questions of all time, and Webb might have the equipment to finally answer it. The telescope’s powerful infrared eyes can analyze the composition of atmospheres of distant worlds, looking for specific elements that are conducive to life or others that may even be direct evidence it’s there.
Water vapor is one key component for habitability, and while JWST has detected it in exoplanet atmospheres before, it’s only done so in Jupiter-like gas giants, which don’t have solid surfaces to (literally) support life. But now, the telescope has detected water vapor in the atmosphere of a rocky Earth-like exoplanet. Maybe.
Located about 26 light-years away, the planet in question is known as GJ 486 b, a Super-Earth about 30% wider and three times more massive than our home planet. But before you pack your bags, it’s worth keeping in mind the gravity there would be stronger, it’s so close to its host star that surface temperatures are about 430 °C (800 °F), and it’s tidally locked so you’d have to pick between permanent day or night.
Habitability may be off the table, but detecting water vapor in the atmosphere of GJ 486 b would still be a big deal. Not only would it be the first-ever direct detection of an atmosphere around a rocky exoplanet, but it would show that these very hot worlds can hang onto their atmospheres despite being blasted by radiation from their host stars. That in itself would have major implications for other potentially habitable planets.
And sure enough, the JWST has detected what seems to be water vapor on GJ 486 b. As the planet passes across the face of the star, the light streams through the atmosphere (if there is one) and creates a signal that astronomers can analyze to figure out the elements present. After watching two of these events, and analyzing the data through three different methods, the team identified a signal that seems to be water vapor.
However, there’s a catch. The team couldn’t rule out that the water vapor signal was actually coming from the star itself instead. Starspots are much cooler than the rest of the star’s surface and can be home to water vapor, including on our own Sun. This could have given off a false positive.
“We didn't observe evidence of the planet crossing any starspots during the transits,” said Ryan MacDonald, co-author of the study. “But that doesn't mean that there aren't spots elsewhere on the star. And that's exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere.”
Thankfully, Webb has ways to check. Its other instruments can study the planet at shorter infrared wavelengths to better determine where the signal is coming from, and figure out whether the planet has an atmosphere. For instance, in an upcoming mission the Mid-Infrared Instrument (MIDI) will be used to find the hottest point on the planet. Without an atmosphere that point should be right in the center of the day side, but if there is an atmosphere, heat will be able to circulate and the hottest point will be elsewhere.
Either way, this is a world worth keeping an eye on.
The research is due to be published in The Astrophysical Journal Letters (PDF).