 The craters are simple in structure : bowl @-@ shaped with no flat bottoms and no central peaks . They are distributed evenly around Ida , except for a protrusion north of crater <unk> which is smoother and less cratered . The ejecta excavated by impacts is deposited differently on Ida than on planets because of its rapid rotation , low gravity and irregular shape . Ejecta blankets settle asymmetrically around their craters , but fast @-@ moving ejecta that escapes from the asteroid is permanently lost . 
