Phobos: Doomed Moon of Mars . ... Mars Express , DLR , ESA Explanation: This moon is doomed. ... The largest moon, Phobos , is indeed seen to be a cratered, asteroid-like object in this stunning new color image from the Mars Express spacecraft, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. ...