Elara (moon)

Infobox Planet
name = Elara
bgcolour = #ffc0c0
discovery = yes


discoverer = C. D. Perrine
discovered = January 2, 1905cite journal| last=Perrine|first=C. D.|title=Satellites of Jupiter|journal=Harvard College Observatory Bulletin |volume=178|date=1905 February 27 |url=http://adsabs.harvard.edu//full/seri/BHarO/0178//0000001.000.html] cite journal| last=Perrine| first=C. D.|title=The Seventh Satellite of Jupiter|journal=Publications of the Astronomical Society of the Pacific| year=1905| volume=17| issue=101|pages= 62–63|url=http://adsabs.harvard.edu//full/seri/PASP./0017//0000062.000.html]
mean_orbit_radius = 11,740,000 km (0.07810 AU)cite journal| last=Jacobson| first=R. A.|title=The orbits of outer Jovian satellites|journal=Astronomical Journal| year=2000| volume=120| pages=2679–2686|doi=10.1086/316817]
eccentricity = 0.22
period = 259.64 d (0.708 a)
avg_speed = 3.27 km/s
inclination = 26.63° (to the ecliptic) 30.66° (to Jupiter's equator)
satellite_of = Jupiter
physical_characteristics = yes
mean_radius = 43 km
surface_area = ~23,200 km²
volume = ~333,000 km³
mass = 8.7e|17 kg
density = 2.6 g/cm³ (assumed)
surface_grav = ~0.031 m/s² (0.003 g)
escape_velocity = ~0.052 km/s
sidereal_day = ~0.5 d (12 h)
albedo = 0.04 (assumed)
single_temperature = ~124 K

Elara (pron-en|ˈɛlərə respell|EL|ər-ə, or as in Greek "Ελάρα)" is a prograde irregular satellite of Jupiter. It was discovered by Charles Dillon Perrine at Lick Observatory in 1905 and is named after the mother by Zeus of the giant Tityus.cite journal| last=Marsden|first=B. G.|title=Satellites of Jupiter|journal=IAUC Circular |volume=2846|date=7 October 1974|url=http://cfa-www.harvard.edu/iauc/02800/02846.html]

Elara did not receive its present name until 1975; before then, it was simply known as nowrap|Jupiter VII. It was sometimes called "Hera"cite book| last=Payne-Gaposchkin|first=Cecilia|coauthors=Katherine Haramundanis|title=Introduction to Astronomy|year=1970|publisher=Prentice-Hall|location=Englewood Cliffs, N.J.|isbn=0-134-78107-4] between 1955 and 1975.

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.

New Horizons encounter

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

ee also

*Irregular satellites
*Jupiter's moons in fiction

References

External links

* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Elara Elara Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://www.ifa.hawaii.edu/~jewitt/irregulars.html David Jewitt pages]
* [http://www.ifa.hawaii.edu/~sheppard/satellites/jupsatdata.html Scott Sheppard pages]