The formation of Stickney Crater, which is nearly half the size of Phobos, may have come close to tearing the moon apart. The prominent grooves are shallow, elongated depressions that may be fractures from the Stickney impact. Individual boulders more than 160 feet (50 meters) wide can be seen on the crater's near rim in this image from Mars Global Surveyor, which flew past Phobos on August 19, 1998.