Elara (moon)

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Elara
Elara2-LB1-mag17.jpg
Elara near the glare of bright Jupiter
Discovery
Discovered by C. D. Perrine
Discovery date January 2, 1905[1][2]
Orbital characteristics
Mean orbit radius
11,740,000 km (0.07810 AU)[3]
Eccentricity 0.22[3]
259.64 d (0.708 a)[3]
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]
~23,200 km2
Volume ~333,000 km3
Mass 8.7×1017 kg
Mean density
2.6 g/cm3 (assumed)[4]
~0.031 m/s2 (0.003 g)
~0.052 km/s
~0.5 d (12 h)
Albedo 0.04 (assumed)[4]
Temperature ~124 K
16.3[4]

Elara (/ˈɛlərə/ EL-ər-ə; Greek: Ελάρα) is a prograde irregular satellite of Jupiter. It was discovered by Charles Dillon Perrine at Lick Observatory in 1905.[1][2] 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.[5]

Elara did not receive its present name until 1975; before then, it was simply known as Jupiter VII. It was sometimes called "Hera"[6] 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 moon in the Himalia group. 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°.[3] Its orbital elements are as of January 2000. They are continuously changing due to solar and planetary perturbations.

New Horizons encounter[edit]

In February and March 2007, the New Horizons spacecraft to Pluto captured Elara in several LORRI images from a distance of five million miles.

See also[edit]

References[edit]

  1. ^ a b Perrine, C. D. (1905-02-27). "Satellites of Jupiter". Harvard College Observatory Bulletin 178. 
  2. ^ a b Perrine, C. D. (1905). "The Seventh Satellite of Jupiter". Publications of the Astronomical Society of the Pacific 17 (101): 62–63. JSTOR 40691209. 
  3. ^ a b c d e f Jacobson, R. A. (2000). "The orbits of outer Jovian satellites". Astronomical Journal 120 (5): 2679–2686. Bibcode:2000AJ....120.2679J. doi:10.1086/316817. 
  4. ^ a b c d "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2009-04-03. Retrieved 2009-08-10. 
  5. ^ Marsden, B. G. (7 October 1974). "Satellites of Jupiter". IAUC Circular 2846. 
  6. ^ Payne-Gaposchkin, Cecilia; Katherine Haramundanis (1970). Introduction to Astronomy. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 0-13-478107-4. 

External links[edit]