Limb .-The outer edge of a planetary disk. Lithosphere .-The solid outer portion of a planet. Mass wasting .-A term that includes all processing by which soil and rock materials fail and are transported downslope predominantly en masse by the direct application of gravitational body stresses. Flat topped prominence with cliff-like edges. A large topographic prominence or chain of elevations.
Normal fault .-A break in the surface caused by tensional forces.
Orographie .-Pertaining to mountains, e specially in regard to their location and distribution. Patera .-Irregular crater or a complex one with scalloped edges. Said of the processes, conditions, areas, climates, and topographic features at the immediate margins of former and existing glaciers and ice sheets, and influenced by the cold temperature of the ice. Perihelion .-That point in the orbit of a planet when it is closest to the Sun. Phase angle .-The angle between a line from the Sun to the center of a body and a line from the spacecraft to the center of the same body.