While our discussion so far centers on planets orbiting stars, astronomers have begun observing Jupiter-sized planets that are unconnected to stars. Named, for now, free-floating planets, interstellar planets, rogue planets, orphan planets, or nomad planets, they are believed to have formed around stars and then were ejected by gravitational effects of other planets or nearby stars.
Although only a few free-floating planets have been observed, their very existence allows astrophysicists to estimate how frequently planets get expelled from orbit around stars. Combined with the result that Earth-mass planets should be ejected even more commonly than higher-mass planets, calculations suggest that there may be more free-floating planets in the Milky Way than there are stars.