Chthonian planet

Chthonian planets (/ˈkθoʊniən/, sometimes 'cthonian') are a hypothetical class of celestial objects resulting from the stripping away of a gas giant's hydrogen and helium atmosphere and outer layers, which is called hydrodynamic escape.

The term chthonian was coined by Hébrard et al. and generally refers to Greek chthonic deities from the infernal underground.

These exoplanets orbit very close to their stars and could be the remnant cores of evaporated gas giants or brown dwarfs.

[5] HD 209458 b is an example of a gas giant that is in the process of having its atmosphere stripped away, though it will not become a chthonian planet for many billions of years, if ever.

[7][8] Other researchers dispute this, and conclude CoRoT-7b was always a rocky planet and not the eroded core of a gas or ice giant,[9] due to the young age of the star system.