Planetary Science

Many of the same processes and forces that shaped the inner terrestrial planets into solid bodies also acted to form out of ice and rock the large moons around the outer planets and the larger objects found in the Kuiper Belt. Most of these bodies have settled into a rounded shape from effects of their own gravitation and have differentiated interiors with a rocky core surrounded by a mantle of icy material topped by an outer icy crust. Jupiter’s moons Europa, Ganymede, and Callisto, and Saturn’s largest moon Titan are made of water ice around a rocky core. Some of the largest moons may have subsurface oceans somewhere below their crusts. The dwarf planets Pluto and Eris, and probably Neptune’s moon Triton, all formed in the Kuiper Belt out of material found in comets and also likely have rocky cores surrounded by ice. The heating that has melted ice and produced eruptions on several moons is thought to be due to complex tidal effects from gravitation as the moons orbit their planet and interact with other moons.

Study of Earth’s planetary system has revealed much about the origin, evolution, and essential processes of planetary systems in general. In turn, knowledge of the general principles governing planetary systems has shed new light on Earth. The immediate practical applications of planetary science concern the preservation of Earth’s environment in a state that supports life. The long-term applications of planetary science focus on the evolution of the physical structures of planetary systems and on the search for planets surrounding stars other than the Sun. Scientific agencies in several countries are currently considering proposals for several projects designed to send more robotic probes to other planets, satellites, asteroids, and comets, and to detect planetary systems orbiting stars other than the Sun, particularly planets like Earth.