Double planet the four, small, outer satellites of Pluto. A now-abandoned hypothesis for the origin of the Moon was actually called the "double-planet hypothesis"; the idea was that the Earth and the Moon formed in the same region of the solar system's proto-planetary disk, forming a system under gravitational interaction. This idea, too, is a problematic condition for defining two bodies as "double planets" because planets can "capture" moons through gravitational interaction. For example, the moons of Mars (Phobos and Deimos) are thought to be asteroids captured long ago by Mars. Such a weak definition would also deem Neptune-Triton a double planet,
Mars in culture in film. The theme of a Martian colony that fights for independence from Earth is a major plot element in the novels of Greg Bear as well as the movie "Total Recall" (based on a short story by Philip K. Dick) and the television series "Babylon 5". Some video games also use this element, including "Red Faction" and the "Zone of the Enders" series. Mars (and its moons) were also the setting for the popular "Doom" video game franchise and the later "Martian Gothic". Mars in culture Mars in culture is about the planet Mars in culture. For example, the