A Field Guide to Alien Planets

Rogue planets

A rogue planet is a planet-sized object that has been ejected from its system and is no longer gravitationally bound to any star, so it orbits the galaxy directly. To become a rogue planet, a planetary-mass object would have to be ejected from its solar system, making it starless. This could be achieved by the competing gravitational forces of the sun and larger planets. Also known as interstellar planet, or orphan planet, a rogue planet would require geothermal activity in to sustain life without energy from a star.