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 Base Camp its moons (Deimos and Phobos), and serve as a proving ground in preparing humans for future missions to the Martian surface. The concept was published in May 2016 by Lockheed Martin, and it is a design for a spacecraft for carrying humans to Mars orbit and conducting operations in Mars orbit. Mars Base Camp harnesses many NASA technologies in development, or technology goals at the time of the 2010s. In September 2017, the plan was updated including a concept for a reusable crewed shuttle called MADV (Mars Ascent Descent Vehicle), which would connect to the MBC Mars space station. Mars