For the first time, a glowing giant exoplanet has been found surrounded by an atmosphere similar to Earth’s. The planet WASP-121b, which lies 270 light years away from Earth, is the first exoplanet found with a stratosphere – an upper layer in its atmosphere. WASP-121b is what is known as a ‘hot Jupiter’ – a gas giant like Jupiter but much hotter, with an orbit that takes it feverishly close to its star.
The researchers used the Hubble space telescope to detect glowing water molecules in the atmosphere of WASP-121b. The glowing water implies the upper layers of the atmosphere must be hotter than the lower layers, meaning it has a stratosphere.
Water has been detected in hot Jupiter atmospheres before, so this was not surprising,” Tom Evans, from the University of Exeter and lead author of the study, told WIRED. “However, the fact that the water was so hot that it was glowing, rather than blocking out light from deeper layers of the atmosphere, was a new result.
Stratospheres in hot Jupiters had been predicted by theory, and observational evidence for them had been obtained previously in a few cases, such as the gas giant WASP-33b.