Over a period of a million years or more, the dust particles stick together, forming larger and larger grains.
Eventually, the grains collect to form planetesimals which eventually coalesce into a planet.
At the same time, the gravity of the planet attracts an atmosphere of gas from the disk.
The theory predicts that a planet’s most abundant element will be oxygen, which would take the form of water vapor in the atmosphere.
The very low levels of water vapor discovered in the atmospheres of HD 189733b, HD 209458b and WASP-12b raise questions about our understanding of the chemical processes involved in planet formation.
Located between 60 and 900 light-years away from Earth, these exoplanets belong to a class of planets known as hot Jupiters. They have average temperatures between 900 and 2,200 degrees Celsius and were thought to be ideal candidates for detecting water vapor in their atmospheres.
