GANYMEDE

Greek Ganymedes, Latin Ganymedes, or Catamitus, in Greek legend, the son of Tros (or Laomedon), king of Troy. Because of his unusual beauty, he was carried off either by the gods or by Zeus, disguised as an eagle, or, according to a Cretan account, by Minos, to serve as cupbearer. In compensation, Zeus gave Ganymede's father a stud of immortal horses (or a golden vine). From early times it was believed that Ganymede's kidnapper had a homosexual passion for him, hence the term catamite, derived from the popular Latin form of his name. He was later identified with the constellation Aquarius. Natural-colour image of Ganymede, one of Jupiter's satellites, taken by the Galileo also called Jupiter III, largest satellite of Jupiter. One of the Galilean satellites, it was discovered by the Italian astronomer Galileo Galilei in 1610 and named by the German astronomer Simon Marius after a figure in Greek mythology. The largest satellite in the solar system, Ganymede has a diameter of about 5,262 km (3,262 miles) and is larger than the planet Mercury. It orbits Jupiter at a distance of 1,070,000 km (663,400 miles). The satellite's relatively low density of 1.93 grams per cubic cm indicates that its composition is roughly half rock and half ice by mass. Heat from formation by accretion and from decay of radioactive elements may have caused differentiation early in Ganymede's history, forming a core of rock surrounded by a thick layer of ice. Craters on Ganymede, one of the satellites of Jupiter. The bright areas in the craters are thought Ganymede was observed at close range in 1979 by the U.S. Voyager 1 and 2 planetary probes and by the Galileo spacecraft in the late 1990s. It has two principal types of terrain, one dark and one bright. The dark terrain is present in broad, roughly polygonal regions that are separated by bands of the bright terrain. Both terrains have impact craters. The density of craters is higher in the dark terrain, indicating that it is the older of the two units. Craters of a given diameter are generally much shallower than craters of the same diameter on rocky bodies, suggesting the relaxation of Ganymede's topography by cold viscous flow of the ice-rich crust. Many of the craters have rays consisting of very bright ice deposits. They are similar in form to those associated with certain lunar craters. Two craters on Ganymede, one of the satellites of Jupiter. Nergal crater, the larger of the two, is Much of the bright terrain is covered by complex patterns of long, narrow topographic grooves. These grooves are typically several hundred metres deep and may be hundreds of kilometres long. They often lie in parallel sets, with adjacent grooves spaced about 510 km (36 miles) apart. The bright terrain in the grooves was probably formed during a period of tectonic activity in which internally generated stresses disrupted and fractured the crust. The exact time at which this activity occurred is not known, but the density of craters in the bright terrain suggests that it was early in Ganymede's history.