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,
A Beautiful Planet does not have a planetary magnetic field. Consequently, "its atmosphere was ripped away from the planet by the solar wind. If you could stand on Mars today, you would find a landscape of lifeless desolation; very cold, and very dry." One of the current challenges in maintaining Earth's planetary "life support system" is global warming. The film shows how Earth's warming climate is causing the Greenland ice sheet to melt, and drives the point home by showing the Jakobshavn Glacier calving an incredibly large number of icebergs in relatively rapid succession as the end of this flowing river of ice