Planet TWA5B is a young exoplanet giant, 25 times heavier than Jupiter, made mostly of hydrogen and helium and orbiting a pair of red dwarfs in the constellation Hydra. Its atmosphere is surprisingly clear: by spreading its light into a rainbow (spectroscopy), astronomers peered through it like clean glass and found no sandy haze. Instead, they spotted signatures of water and carbon monoxide (CO, with carbon and oxygen), and then an unexpected trace: gaseous silicon monoxide (SiO).

On Earth, this gas would instantly clump into sand, but at 2400 °C the silicon drifts freely, never forming clouds. This is the first solid detection of gaseous silicon in a directly imaged planet’s atmosphere. The abundance of SiO reveals it was born far from its star, where the planet-forming disk was loaded with icy grains. No sandy silicate dust fogs the view: we can see straight through to the atmosphere’s depths.

From now on, this gas acts as a telltale: if SiO is scarce on a cooler planet, dense sand clouds are hiding it. Future JWST observations will apply this diagnosis to other scorching worlds.