Moons of Mars these 'predictions', two craters on Deimos are named Swift and Voltaire, while on Phobos there is one named regio, "Laputa Regio", and one named planitia, "Lagado Planitia", both of which are named after places in "Gulliver's Travels" (the fictional Laputa, a flying island, and Lagado, imaginary capital of the fictional nation Balnibarbi). Many of the craters on Phobos are also named after characters in "Gulliver's Travels". Asaph Hall discovered Deimos on 12 August 1877 at about 07:48 UTC and Phobos on 18 August 1877, at the US Naval Observatory in Washington, D.C., at about 09:14 GMT (contemporary sources, using the
Moons of Mars its 30-hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars. Both moons are tidally locked, always presenting the same face towards Mars. Since Phobos orbits Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. At some point in the future, when it approaches Mars closely enough (see Roche limit), Phobos will be broken up by these tidal forces. Several strings of craters on the Martian surface, inclined further from the equator the older they are, suggest that there may have been