Chthonian planet rocky planet and not the eroded core of a gas or ice giant, due to the young age of the star system. Kepler-70b and Kepler-70c are sub-Earth planets that are thought to have been giant planets that were engulfed by the extended envelope of their star in its red giant phase vaporizing their gaseous envelope. Chthonian planet Chthonian planets (, 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. Such atmospheric stripping is a likely result of proximity to
Nova two evolves into a red giant, leaving its remnant white dwarf core in orbit with the remaining star. The second star—which may be either a main sequence star or an aging giant—begins to shed its envelope onto its white dwarf companion when it overflows its Roche lobe. As a result, the white dwarf steadily captures matter from the companion's outer atmosphere in an accretion disk, and in turn, the accreted matter falls into the atmosphere. As the white dwarf consists of degenerate matter, the accreted hydrogen does not inflate, but its temperature increases. Runaway fusion occurs when the temperature of