Amalthea is the third of Jupiter's known satellites:
orbit: 181,300 km from Jupiter
diameter: 189 km (270 x 166 x 150)
mass: 3.5e18 kg ?
Amalthea was the nymph who nursed the infant Jupiter with goat's milk.
Discovered by Barnard 1892 September 9 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).
Amalthea and Himalia are Jupiter's fifth and sixth largest moons; they are about the same size but only 1/15 the size of next larger one, Europa.
Like most of Jupiter's moons, Amalthea rotates synchronously; its long axis is pointed toward Jupiter.
Amalthea is the reddest object in the solar system. The reddish color is apparently due to sulfur originating from Io.
Earlier, it was thought that its size and irregular shape should imply that Amalthea is a fairly strong, rigid body. But measurements of its mass made during Galileo's last orbit indicate otherwise. It now appears that Amalthea's density is only about the same as water and since it is unlikely to be composed of ice it is most likely a loose rubble pile with a lot of empty spaces.
Like Io, Amalthea radiates more heat than it receives from the Sun (probably due to the electrical currents induced by Jupiter's magnetic field).
公转轨道：距木星 181,300 千米