Deimos and Phobos Interior Explorer that the moons of Mars may have formed after a huge collision with a protoplanet one third the mass of Mars that formed a ring around Mars. A third hypothesis is that they may have co-accreted with the parent planet. DePhine mission would explore the origin and the evolution of the two Martian satellites, by focusing on their interior structures and diversity. The mission would attempt to determine if Phobos and Deimos true siblings, originating from the same source and sharing the same formation scenario. It would also determine if both natural satellites are rubble piles or solid bodies, and
Definition of planet spherical under its own gravity but not large enough to fuse. This definition would add 19 moons to the list of planets in our Solar System. The discovery since 1992 of extrasolar planets, or planet-sized objects around other stars ( such planets in planetary systems including multiple planetary systems as of ), has widened the debate on the nature of planethood in unexpected ways. Many of these planets are of considerable size, approaching the mass of small stars, while many newly discovered brown dwarfs are, conversely, small enough to be considered planets. The material difference between a low-mass star and