Elara (moon)

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Elara
Discovery
Discovered by C. D. Perrine
Discovery time January 2, 1905[1][2]
Orbit
Avgdistance from the center of its orbital path 11,740,00 km (0.07810 AU)[3]
How egg-shaped its orbit is
("eccentricity")
0.22[3]
How long it takes to complete an orbit 259.64 d (0.708 a)[3]
Average speed 3.27 km/s[3]
Angle above the reference plane
("inclination")
26.63° (to the ecliptic)
30.66° (to Jupiter's equator)[3]
What it orbits Jupiter
Size and Other Qualities
Average distance from its center to its surface 43 km
Area of its surface ~23,200 km2
Volume inside it ~333,000 km3
Mass 8.7×1017 kg
Average density 2.6 g/cm3 (assumed)
Gravity at its surface ~0.031 m/s2 (0.003 g)
Slowest speed able to escape into space
("escape velocity")
~0.052 km/s
How long it takes to turn around one time
(in relation to the stars)
~0.5 d (12 h)
How much light it reflects 0.04 (assumed)
Avg. surface temp. ~124 K

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.[4]

Elara did not get its present name until 1975; before then, it was simply known as Jupiter VII. It was sometimes called "Hera"[5] 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[change | change source]

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.

References[change | change source]

  1. 1.0 1.1 Perrine, C. D. (1905 February 27). "Satellites of Jupiter". Harvard College Observatory Bulletin 178. http://adsabs.harvard.edu//full/seri/BHarO/0178//0000001.000.html.
  2. 2.0 2.1 Perrine, C. D. (1905). "The Seventh Satellite of Jupiter". Publications of the Astronomical Society of the Pacific 17 (101): 62–63. http://adsabs.harvard.edu//full/seri/PASP./0017//0000062.000.html.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Jacobson, R. A. (2000). "The orbits of outer Jovian satellites". Astronomical Journal 120: 2679-2686. doi:10.1086/316817 .
  4. Marsden, B. G. (7 October 1974). "Satellites of Jupiter". IAUC Circular 2846. http://cfa-www.harvard.edu/iauc/02800/02846.html.
  5. Payne-Gaposchkin, Cecilia; Katherine Haramundanis (1970). Introduction to Astronomy. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 0-134-78107-4 .

Other websites[change | change source]