Britannica Sources used in this answer

Could a rogue planet support liquid water without orbiting a star?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Extrasolar planet Artist's conception of the extrasolar planet HD 209458b, some 150 light-years from Earth.

While it is often assumed that rogue planets are icy and incapable of supporting life because they do not orbit a star, it is scientifically conjectured that they could potentially sustain liquid water.

For a rogue planet to maintain liquid water on its surface, it would likely need to retain its original hydrogen-helium atmosphere and possess internal radioactive heating to generate sufficient warmth.1

Additionally, the moons of rogue planets might provide hospitable environments. If a moon is large enough, it could generate tidal friction to heat the planet, while a thick carbon dioxide atmosphere could trap that heat, allowing liquid water to survive beneath the surface. These internal energy sources, such as radioactive decay and tidal heating, are recognized in astronomy as mechanisms capable of warming a planet to the melting point of water, independent of a star's habitable zone.12