Elara (moon)

Discovery and name

Elara was discovered in 1905 by astronomer Charles Dillon Perrine at Lick Observatory. For many decades it was known only by the designation Jupiter VII. Between 1955 and 1975 it was occasionally listed under the name "Hera," but that name conflicted with other mythological assignments and was not adopted. In 1975 the moon received its modern name, Elara, after a figure in Greek mythology associated with Zeus.

Physical characteristics

Elara is relatively small compared with Jupiter’s major moons and is irregularly shaped rather than spherical. Its surface appears dark and low in reflectivity, a trait common to many outer irregular satellites. Spectral observations suggest a surface composition broadly similar to carbonaceous (C‑type) or D‑type small bodies — a mixture of rock and darker, likely carbon-rich material — but detailed compositional information is limited by its distance and size.

Orbit and group association

Elara belongs to the Himalia group, a cluster of prograde irregular moons that orbit Jupiter at distances roughly between 11,000,000 and 13,000,000 kilometers and share similar orbital inclinations near 27–28 degrees. Members of this group are thought to share a common origin, perhaps fragments of a captured parent body. Because Elara orbits far from Jupiter, its orbital elements vary over time under the influence of solar and planetary perturbations.

Observations and scientific importance

• Elara has been tracked by ground-based telescopes since its discovery; precise spacecraft flybys have been limited or nonexistent, so high-resolution imaging remains scarce.
• Studying Elara and its fellow Himalia-group moons helps scientists understand capture processes, collisional histories, and the population of irregular satellites around giant planets.
• Comparative studies of spectral properties across the group assist in testing whether the members share a common parent body or represent a diverse collection of captured objects.

For general background on Jupiter’s irregular moons and recent catalogues, see discovery records, observatory archives, and compilations of satellite names and designations at naming resources. Historical discussions about the temporary use of the name "Hera" and the formal adoption of Elara are noted in mythology and naming histories and official naming lists published in the 1970s. More on the Himalia group and orbital parameters may be found in orbital surveys and dynamical studies referenced at group studies and orbital data compilations.