Elara (moon)

Elara is a non-spherical moon of Jupiter. It was found by Charles Dillon Perrine at Lick Observatory in 1905^[1][2] and is named after the mother by Zeus of the giant Tityus.^[5]

Elara

Elara near the glare of bright Jupiter
Discovery
Discovered by	C. D. Perrine
Discovery date	January 5, 1905[1][2]
Orbital characteristics
Mean orbit radius	11,740,000 km (0.07810 AU)[3]
Eccentricity	0.22[3]
Orbital period	259.64 d (0.708 a)[3]
Average orbital speed	3.27 km/s[3]
Inclination	26.63° (to the ecliptic) 30.66° (to Jupiter's equator)[3]
Satellite of	Jupiter
Physical characteristics
Mean radius	43 km[4]
Surface area	~23,200 km2
Volume	~333,000 km3
Mass	8.7×1017 kg
Mean density	2.6 g/cm3 (assumed)[4]
Surface gravity	~0.031 m/s2 (0.003 g)
Escape velocity	~0.052 km/s
Sidereal rotation period	~0.5 d (12 h)
Albedo	0.04 (assumed)[4]
Temperature	~124 K
Apparent magnitude	16.3[4]

Elara did not get its present name until 1975; before then, it was simply known as Jupiter VII. It was sometimes called "Hera"^[6] between 1955 and 1975.

Elara belongs to the Himalia group, five moons orbiting between 11,000,000 and 13,000,000 km from Jupiter at an inclination of about 27.5°.^[3] Its orbital elements are as of January 2000. They are changing a lot due to Solar and planetary perturbations.

New Horizons encounter

In February and March 2007, the New Horizons spacecraft to Pluto made a number of pictures of Elara, culminating in photos from a distance of five million miles.