Leda (moon)

Lore & Background

Leda was discovered by Charles T. Kowal at the Mount Palomar Observatory on September 14, 1974, after three nights' worth of photographic plates had been taken from September 11 through 13; Leda appears on all of them. It was named after Leda, who was raped by Zeus, the Greek equivalent of Jupiter (who came to her in the form of a swan). Kowal suggested the name and the IAU endorsed it in 1975.

Leda orbits Jupiter at an average distance of 11,195,980 km in 242.02 days, at an inclination of about 28° to the ecliptic, in a prograde direction and with an eccentricity of 0.165. It belongs to the Himalia group, a prograde group of moons orbiting between 11 and 13 million km from Jupiter at inclinations between 27 and 30°, and eccentricities between 0.11 and 0.24.

Leda has a diameter of about 21.5 kilometers, with a measured albedo of about 3.4%. Like the other members of the Himalia group, the satellite appears gray (color indices B-V=0.66 ± 0.01, R-V=0.43 ± 0.01), which is typical for C-type asteroids. Leda probably did not form near Jupiter but was captured by Jupiter later. Like the other members of the Himalia group, which have similar orbits, Leda is probably the remnant of a broken, captured heliocentric asteroid.

Reader's Guide

Leda is significant as one of the innermost irregular satellites of Jupiter, discovered in 1974 by Charles T. Kowal at Mount Palomar Observatory. Its discovery, based on photographic plates taken over three nights, added a new member to Jupiter's irregular satellite family. The moon's naming after Leda, who was raped by Zeus (the Greek equivalent of Jupiter), follows the mythological naming convention for Jovian moons. Leda's orbital characteristics—average distance of 11,195,980 km, period of 242.02 days, inclination of about 28°, and eccentricity of 0.165—place it firmly within the Himalia group, a prograde group of moons with similar orbits. Its physical properties, including a diameter of about 21.5 km and a low albedo of about 3.4%, along with its gray color typical of C-type asteroids, suggest a captured origin. Leda likely did not form near Jupiter but was captured later, and along with other Himalia group members, is probably the remnant of a broken, captured heliocentric asteroid. This makes Leda important for understanding the capture history and collisional evolution of Jupiter's irregular satellite system.