AMALTHEIA, in Greek mythology, the foster-mother of Zeus. She is sometimes represented as the goat which suckled the infant-god in a cave in Crete, sometimes as a nymph of uncertain parentage (daughter of Oceanus, Haemonius, Olen, Melisseus), who brought him up on the milk of a goat. This goat having broken off one of its horns, Amaltheia filled it with flowers and fruits and presented it to Zeus, who placed it together with the goat amongst the stars. According to another story, Zeus himself broke off the horn and gave it to Amaltheia, promising that it would supply whatever she desired in abundance. Amaltheia gave it to Acholous (her reputed brother), who exchanged it for his own horn which had been broken off in his contest with Heracles for the possession of Deianeira. According to ancient mythology, the owners of the horn were many and various. Speaking generally, it was regarded as the symbol of inexhaustible riches and plenty, and became the attribute of various divinities (Hades, Gaea, Demeter, Cybele, Hermes), and of rivers (the Nile) as fertilizers of the land. The term ``horn of Amaltheia is applied to a fertile district, and an estate belonging to Titus Pomponius Atticus was called Amaltheum. Cretan coins represent the infant Zeus being suckled by the goat; other Greek coins exhibit him suspended from its teats or carried in the arms of a nymph (Ovid, Fasti, v. 115; Metam. ix. 87).
Amalthea (pronounced "am al THEE uh") is the third of Jupiter's known moons. It was discovered on September 9 1892 by Edmund Emerson Barnard using the 36 inch (91 cm) refractor at Lick Observatory. Amalthea was the last moon to be discovered by direct visual observation as opposed to photography, and the first since Galileo Galilei discoveredthe Galilean moons in 1610. It is named after the nymph of Greek legend who nursed the infant Jupiter with goat's milk.
Amalthea is the reddest object in the solar system, even redder than the planet Mars. The reddish color is apparently due to sulfur originating from Io. Bright patches of green appear on the major slopes of Amalthea, but the nature of this color is currently unknown.
Amalthea is irregularly shaped and heavily scarred by craters, some of which are extremely large relative to the size of the moon. Pan, the largest crater, measures 100 kilometers across and is at least 8 kilometers deep. Another crater, Gaea, measures 80 kilometers across and is probably twice as deep as Pan. Amalthea has two known mountains, Mons Lyctas and Mons Ida with local relief reaching up to 20 kilometers.
The combination of Amalthea's irregular shape and large size implies that Amalthea is a fairly strong, rigid body; if it were composed of ices or other weak materials its own gravity would have pulled it into a more sphereical shape. Like all of Jupiter's moons it is tidally locked with the planet, its long axis pointing towards Jupiter at all times. Its composition is probably more like an asteroid's than like the Galilean moons, and it may be captured. Like Io, Amalthea radiates more heat than it receives from the Sun. This is probably due to the electrical currents induced within it by its orbit through Jupiter's magnetic field.
- Orbital radius: 181,300 km
- diameter: 189 km (270 x 166 x 150)
- mass: 7.17*1018 kg
- orbital period: 11.92 hours
- orbital inclination: 0.4°
- Mean density: 1.8 g/cm3