Formation and evolution of the Solar System further hypothesized that the Mars-sized object may have formed at one of the stable Earth–Sun Lagrangian points (either or ) and drifted from its position. The moons of trans-Neptunian objects Pluto (Charon) and Orcus (Vanth) may also have formed by means of a large collision: the Pluto–Charon, Orcus–Vanth and Earth–Moon systems are unusual in the Solar System in that the satellite's mass is at least 1% that of the larger body. Astronomers estimate that the Solar System as we know it will not change drastically until the Sun has fused almost all the hydrogen fuel in its core into helium,
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