Chthonian planet

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Artist's conception of COROT-7b.
Artist's conception of HD 209458 b transiting its star.

A chthonian planet (/ˈkθniən/, sometimes 'cthonian') is 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 a star. The remaining rocky or metallic core would resemble a terrestrial planet in many respects.[1]

HD 209458 b is an example of a planet that is in the process of having its atmosphere stripped away, though it is not itself a chthonian planet nor is it expected to become one in the near future.[clarification needed] A similar case would be Gliese 436b, as it has already lost 10% of its atmosphere. [2]

COROT-7b may be the first chthonian planet discovered.[3][4]

Chthonia (from Greek: Χθών) means "of the Earth". The term was coined by Hébrard et al., since the term chthonian generally refers to Greek deities from the infernal underground.

See also[edit]


  1. ^ Hébrard G., Lecavelier Des Étangs A., Vidal-Madjar A., Désert J.-M., Ferlet R. (2003), Evaporation Rate of Hot Jupiters and Formation of chthonian Planets, Extrasolar Planets: Today and Tomorrow, ASP Conference Proceedings, Vol. 321, held 30 June – 4 July 2003, Institut d'astrophysique de Paris, France. Edited by Jean-Philippe Beaulieu, Alain Lecavelier des Étangs and Caroline Terquem.
  2. ^ "Hubble sees atmosphere being stripped from Neptune-sized exoplanet". Nature. 2015-06-24. Retrieved 2015-11-08. 
  3. ^ "Exoplanets Exposed to the Core". AstroBiology Magazine. 2009-04-25. Retrieved 2009-07-13. 
  4. ^ "Super-Earth 'began as gas giant'". BBC News. 10 January 2010. Retrieved 2010-01-10. 
  5. ^ "Planet : CoRoT-7 b". Retrieved 2009-06-13.