Astronomy Picture of the Day . ... 7.11.2009 . ... Credit: HiRISE , MRO , LPL (U. Arizona) , NASA Explanation: Stickney Crater, the largest crater on the martian moon Phobos, is named for Chloe Angeline Stickney Hall, mathematician and wife of astronomer Asaph Hall. ... Even though the surface gravity of asteroid-like Phobos is less than 1/1000th Earth's gravity, streaks suggest loose material has slid down inside the crater walls over time. ... November 2009 . ... 2007 2008 . 2009 2010 . ...