With a mean radius of 18 km (assuming an albedo of 0.04), Lysithea is the second smallest moon in the Himalia group, a family of Jovian satellites which have similar orbits and appearance, and are therefore thought to have a common origin.
Lysithea may be a chunk of an asteroid (a C- or D-class asteroid, judging by the fact that it reflects only about 4% of the light it receives), which was broken apart in a collision either before or after being captured by Jupiter's gravity. In this scenario, the other pieces became the other moons in the Himalia group: Leda, Himalia (the largest) and Elara. A fifth moon, called S/2000 J11, only about 2 km in radius, was considered a candidate for this group. However, it was lost before its orbit could be definitively determined. It may have crashed into Himalia, reuniting two pieces of the former asteroid, and perhaps creating a faint temporary ring of Jupiter near the orbit of Himalia.
At a distance of about 11.7 million km from Jupiter, Lysithea takes about 259 Earth days to complete one orbit.
Lysithea was discovered on 6 July 1938 by Seth Barnes Nicholson with the 100-inch (2.5 m) Hooker telescope at the Mount Wilson Observatory.
How Lysithea Got its Name:
Lysithea was named for one of the lovers of the Roman god Jupiter, or the Greek equivalent, Zeus. In one account, Zeus promised to do whatever Lysithea asked after he impregnated her, and Hera (Zeus' wife and sister) tricked her into asking for Zeus to come to her in the same way he came to Hera when he wooed her. So Zeus rode into Lysithea's bridal chamber in a chariot with lightning and thunder and launched a thunderbolt, setting the room on fire. Lysithea died of fright, but Zeus snatched her six-month fetus from the fire and sewed it into his own thigh so he could carry the child to term. At the appropriate time, Zeus undid the stitches and out popped Dionysus.
A name ending in "a" was chosen for this moon in keeping with the International Astronomical Union's policy for designating Jupiter's outer moons which have prograde orbits (orbiting in the same direction as Jupiter's rotation).