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
Hydrogen a means of expelling reducing equivalents in biochemical reactions. The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water, and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burnt on site, oxygen is desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, for instance, would oxidize, and thus decrease the amount of oxygen given off.)