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:
“Processions that lack high stilts have nothing that catches the eye.
What if my great-granddad had a pair that were twenty foot high,
And mine were but fifteen foot, no modern stalks upon higher,
Some rogue of the world stole them to patch up a fence or a fire.”
—William Butler Yeats (1865–1939)
“Until they saw, over the mists
of Venus, two fish creatures stop
on spangled legs and crawl
from the belly of the sea.
And from the planet park
they heard the new fruit drop.”
—Anne Sexton (1928–1974)