The young star PDS 66 is surrounded by a flat disk of gas and dust — the cradle of future planets. In the cold outer regions of such a disk, silicon and sulfur are usually hidden inside dust grains, but astronomers spotted a bright patch of gas at about 60 astronomical units from the star. It's like finding warm steam over a snowdrift: something heated the ice and released the molecules.
The gas patch turned out to be compact, smaller than the telescope's resolution, and it moves along an orbit as expected for a body in the disk. The authors suggest it's a shell around a growing planet: pebbles falling onto it vaporize and enrich the gas with silicon. Such a "hot pocket" reveals a planet that would otherwise be invisible.
This is the first time gas enriched by vaporized dust has been seen around a protoplanet. Previously, we inferred planet growth from gaps in disks; now we can catch the process itself, like steam rising from a pot where a future planet is simmering.
The molecule SiS, silicon monosulfide, is unstable under terrestrial conditions, but in space it serves as a marker of hot regions where dust vaporizes.