A rogue planet — also known as an interstellar planet, nomad planet, free-floating planet or orphan planet — is a planetary-mass object which has either been ejected from its system or was never gravitationally bound to any star, brown dwarf or other such object, and that therefore orbits the galaxy directly. Astronomers believe that either way, the definition of planet should depend on current observable state and not origin.
Larger planetary-mass objects which were not ejected, but have always been free-floating, are thought to have formed in a similar way to stars, and the IAU has proposed that those objects be called sub-brown dwarfs (an example of this is Cha 110913-773444, which may be an ejected rogue planet, or it may have formed on its own and be a sub-brown dwarf). The closest to earth yet discovered is around 100 light years away.
Read more about Rogue Planet: Observation, Retention of Heat in Interstellar Space, Proplyds of Planetars, Known or Possible Rogue Planets, In Popular Culture
Famous quotes containing the words rogue and/or planet:
“It is said that a rogue does not look you in the face, neither does an honest man look at you as if he had his reputation to establish.”
—Henry David Thoreau (1817–1862)
“I have always believed that opera is a planet where the muses work together, join hands and celebrate all the arts.”
—Franco Zeffirelli (b. 1922)