Amalthea

Discovery
Amalthea was discovered by Edward Emerson Barnard on 9th September 1892.

In-Depth
Amalthea is part of Io's orbit, which is the innermost of the four largest moons of Jupiter (often called the Galilean moons) along with three smaller moons named Metis, Adrastea and Thebe.

All of the moons within this group are oddly shaped, lacking either mass and/or composition to pull themselves into a spherical shape. During its lifetime, the Galileo spacecraft had revealed some surface features, including hills, valleys and impact craters.

Within this group, Amalthea is the largest with a mean radius of 83.5 ± 2.4 kilometres. With a distance of 181,400 kilometres away from Jupiter, Amalthea completes one orbit in 0.498 Earth days.

Amalthea is the reddest object in our solar system and appears to give out more heat than the Sun. This may be due to Jupiter's powerful magnetic field, electric currents are also occurring in the moon's core. Alternatively, the heat could be from tidal stresses.

Amalthea and Thebe rotate on their axe once for each orbit around Jupiter, always keeping the same side facing towards the planet. This rotation takes roughly one and a half Earth days for Amalthea and two thirds for Thebe.

Amalthea and Thebe also provide the material for the Gossamer ring.

Io orbits 422,000 kilometres above Jupiter and at this distance, one would think this satellite would be ripped to pieces due to extreme tidal flexing from Jupiter's gravity. However, because Amalthea is so small (roughly 1/19th of Io's diameter) it is relatively immune to this effect. Amalthea is so close to Jupiter than eventually its orbit will decay and fall into the planet.

Namesake
Originally designated Jupiter V, Camille Flammarion suggested the name Amalthea for this moon. Amalthea is named for a naiad who nursed the newborn Jupiter.