Elara near the glare of bright Jupiter
|Discovered by||C. D. Perrine|
|Discovery date||January 2, 1905|
|Mean orbit radius||11,740,000 km (0.07810 AU)|
|Orbital period||259.64 d (0.708 a)|
|Average orbital speed||3.27 km/s|
|Inclination||26.63° (to the ecliptic)
30.66° (to Jupiter's equator)
|Mean radius||43 km|
|Surface area||~23,200 km2|
|Mean density||2.6 g/cm3 (assumed)|
|Equatorial surface gravity||~0.031 m/s2 (0.003 g)|
|Escape velocity||~0.052 km/s|
|Sidereal rotation period||~0.5 d (12 h)|
Elara (// EL-ər-ə; Greek: Ελάρα) is a prograde irregular satellite of Jupiter. It was discovered by Charles Dillon Perrine at Lick Observatory in 1905. It is the eighth largest moon of Jupiter and is named after Elara, one of Zeus's lovers and the mother of the giant Tityos.
Elara did not receive its present name until 1975; before then, it was simply known as Jupiter VII. It was sometimes called "Hera" between 1955 and 1975. It has a mean radius of just 43 km meaning it is just 2% the size of Europa. However it is half the size of Himalia so it is the second biggest Himalian moon. It might be a captured type C or D asteroid because it reflects very little light.
Elara belongs to the Himalia group, five moons orbiting between 11 and 13 Gm from Jupiter at an inclination of about 27.5°. Its orbital elements are as of January 2000. They are continuously changing due to solar and planetary perturbations.