Space missions have provided extensive information on the other planets and the planetary satellites of the solar system. It appears that plate tectonics is unique to the Earth. The Moon and Mercury have continuous lithospheres
whose surfaces have been shaped largely by impacts and volcanic processes. Although impact cratering and volcanism have also been prevalent on Mars, its surface has also been modified by its atmosphere and the flow of a surface fluid, presumably water. Cloud-covered Venus has yielded its secrets to the eyes of Earth-based and spacecraft radar systems. Cratering and volcanism have extensively modified its surface, but there is no direct evidence of plate tectonic features such as extensive ridge or trench systems. The Galilean satellites of Jupiter have been shown to have very diverse features including very active volcanism on Io. The surface of Ganymede shows impact craters and tectonic structures resulting from dynamical processes in an underlying predominantly ice lithosphere. Callisto is a heavily cratered object about the same size as Ganymede, but there is no sign that its surface has been altered by internal activity. Europa is mainly a rocky object, somewhat smaller than the Moon, with a relatively thin outer shell of water that is ice at the surface but may be liquid at depth.The surface of Io has been recently formed by a style of volcanism apparently unique to that body. Io is the only body in the solar system, other
than the Earth, on which we have observed active volcanism; this satellite is the most volcanically active body in the solar system. Lithospheric plate evolution has destroyed much of the evidence of the early evolution of the
Earth by continuously creating new surface rocks and returning old surface rocks to the mantle. The pervasive volcanism of Io has had the same effect by blanketing the surface with recently formed lavas. However, bodies such
as Mercury, the Moon, Callisto, and the satellites of Mars preserve the early records of their evolutions in their cratered surfaces and thereby provide information on the early history of the solar system.