Leda was discovered on Sept. 14, 1974 by Charles Thomas Kowal on plates taken from Sept. 11 through 13, 1974 with the 122-cm Schmidt telescope at Mount Palomar.


With a mean radius of 6.2 miles (10 kilometers), assuming an albedo of 0.04, Leda is the 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.

Leda 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: Himalia (the largest), Lysithea 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 6.9 million miles (11.2 million kilometers) from Jupiter, Leda takes nearly 241 Earth days to complete one orbit.

How Leda Got its Name

Leda was named for a woman in Greek mythology. According to one legend, she was seduced by Zeus (the Greek equivalent of the Roman god, Jupiter), who had taken the form of a swan. This pairing was depicted by a number of artists, including Leonardo da Vinci and Michelangelo. In this story, she bore Zeus two children: Pollux and Helen.

However, in another account, Helen was the offspring of Zeus (in the form of a swan) and Nemesis (in the form of a goose). According to this legend, Nemesis laid an egg following her encounter with Zeus, which a shepherd brought to Leda. Helen hatched out of the egg, and Leda raised her as her own daughter.

The moon's discoverer, Charles T. Kowal, opposed the naming of the satellite, siding with a number of astronomers of the time who preferred the old numbering system. He suggested "Leda" if names were nevertheless to be assigned.

A name ending in "a" was chosen 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)

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