 The curvilinear gullies end in lobate deposits, which are sometimes covered by pitted terrain, and are proposed to form by the transient flow of liquid water after buried deposits of ice were melted by the heat of the impacts.Hydrated materials have also been detected, many of which are associated with areas of dark material.Consequently, dark material is thought to be largely composed of carbonaceous chondrite, which was deposited on the surface by impacts.