Stickney Crater on Phobos The Doomed Moon Phobos is one of the two moons of Mars. Phobos is expected to break up and form a ring around Mars.  ESA, DLR, FU Berlin, Mars Express; Processing & CC BY 2.0 License: Andrea Luck Stickney Crater Stickney Crater on Phobos is the largest crater on the Moon, named after Chloe Angeline Stickney.  HiRISE, MRO, LPL (U. Arizona), NASA Chloe Angeline Stickney Stickney was the wife of astronomer Asaph Hall who discovered Phobos and Deimos in 1877.  HiRISE, MRO, LPL (U. Arizona), NASA Size The crater is about nine kilometres wide, which is almost half the diameter of Phobos itself.  HiRISE, MRO, LPL (U. Arizona), NASA Formation The formation of the Stickney crater was so violent, that the asteroid almost disintegrated from the impact event.  Viking Project, JPL, NASA; Image mosaic by Edwin V. Bell II (NSSDC/Raytheon ITSS) Age Though the age of the Stickney crater is not definitively known, evidence suggests it is not the oldest feature.  Viking Project, JPL, NASA Secondary Craters There are a number of secondary craters and grooves along the surface of Phobos.  ESA/DLR/FU Berlin Stress Fractures The grooves or ridges can extend for kilometres, and are stress fractures caused by the impact event.  NASA Shape Because of the irregular shape of Phobos, and the angle of impact, the crater is oval instead of round.  NASA/JPL/Malin Space Science Systems Interior There are landslides and slumping along the interior of the crater walls, a common feature in large craters.  NASA/JPL/Malin Space Science Systems