Adrastea

Discovery
Adrastea was discovered by the Voyager science team in July 1979.

In-Depth
Metis, Adrastea, Amalthea and Thebe are currently orbiting Io (which is the innermost of the four largest moons, often called the Galilean moons).

All of these moons are oddly shaped within this group, lacking either mass and/or composition to allow spherical shapes to form. During its lifetime, the Galilean spacecraft had revealed surface features, including hills, valleys and impact craters.

Within this group, Adrastea is the smallest having a mean radius of 8.2 ± 2.0 kilometres. Averaging a distance of 129,000 kilometres, Adrastea takes 0.298 Earth days to complete one orbit. We currently don't know the rotational period for Adrastea, but we do know that its orbital period lasts 7 hours (the time it takes to return to where the orbit began).

Adrastea is subjected to extreme tidal flexing from Jupiter's gravity, since Io orbits 422,000 kilometres above Jupiter, one would imagine that the satellite would shred to pieces. However, because Adrastea is so small it's relatively immune to the tidal forces effects. Adrastea is one of the two closest moons in Jupiter's orbit (the other being Metis) that orbit inside the synchronous orbit radius. This means that Adrastea orbits Jupiter faster than a Jovian day. Adrastea's orbit will eventually decay and fall into the planet due to it being so far from Jupiter.

Adrastea and Metis also sit inside Jupiter main ring and are, undoubtedly, the main source of material for this ring.

Namesake
Adrastea is named after the Cretian nymph who took care of Zeus for his mother Rhea.