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
Minor-planet moon Minor-planet moon A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. It is thought that many asteroids and Kuiper belt objects may possess moons, in some cases quite substantial in size. Discoveries of minor-planet moons (and binary objects, in general) are important because the determination of their orbits provides estimates on the mass and density of the primary, allowing insights of their physical properties that is generally not otherwise possible. The first modern era mention of the possibility of an asteroid satellite was in connection with an occultation of the bright star Gamma