Formation and evolution of the Solar System System bodies have been created by both collisions and capture. Mars's two small moons, Deimos and Phobos, are thought to be captured asteroids. The Earth's Moon is thought to have formed as a result of a single, large head-on collision. The impacting object probably had a mass comparable to that of Mars, and the impact probably occurred near the end of the period of giant impacts. The collision kicked into orbit some of the impactor's mantle, which then coalesced into the Moon. The impact was probably the last in the series of mergers that formed the Earth. It has been
Phobos (moon) who studied Phobos and people and places from Jonathan Swift's "Gulliver's Travels". A number of craters have been named, and are listed in the following table. There is one named regio, "Laputa Regio", and one named planitia, "Lagado Planitia"; both are named after places in "Gulliver's Travels" (the fictional Laputa, a flying island, and Lagado, imaginary capital of the fictional nation Balnibarbi). The only named ridge on Phobos is "Kepler Dorsum", named after the astronomer Johannes Kepler. The orbital motion of Phobos has been intensively studied, making it "the best studied natural satellite in the Solar System" in terms of