Himalia (moon)
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Himalia as seen by Cassini-Huygens
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Discovery
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| Discovered by | C. D. Perrine |
| Discovery date | December 16, 1904 |
| Periapsis | 9,782,900 km |
| Apoapsis | 13,082,000 km |
| Mean orbit radius | 11,460,000 km[1] |
| Eccentricity | 0.16[1] |
| Orbital period | 250.56 d (0.704 a)[1] |
| Average orbital speed | 3.312 km/s |
| Inclination | 27.50° (to the ecliptic) 29.59° (to Jupiter's equator)[1] |
| Satellite of | Jupiter |
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Physical characteristics
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| Mean radius | 85 km[2] |
| Surface area | ~90,800 km² |
| Volume | ~2,570,000 km³ |
| Mass | 6.7 × 1018 kg[2] 4.19 × 1018 kg[3] |
| Mean density | 2.6 g/cm³ (assumed)[2] 1.63 g/cm³ (assuming radius 85km)[3][4] |
| Equatorial surface gravity | ~0.062 m/s2 (0.006 g) |
| Escape velocity | ~0.100 km/s |
| Sidereal rotation period |
~0.4 d (10 h) |
| Albedo | 0.04[2][5] |
| Temperature | ~124 K |
Himalia (pronounced /haɪˈmeɪliə/ hye-MAY-lee-ə, or /hɪˈmɑːliə/ hi-MAH-lee-ə as in Greek ‘Ιμαλíα) is the largest irregular satellite of Jupiter, and the sixth largest. It was discovered by Charles Dillon Perrine at the Lick Observatory on 1904 December 3[6] and is named after the nymph Himalia who bore three sons of Zeus (the Greek equivalent of Jupiter).
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[edit] Discovery
Himalia, the largest irregular satellite of Jupiter, was discovered by Charles Dillon Perrine at the Lick Observatory on 1904 December 3.[6]
[edit] Name
Himalia is named after the nymph Himalia who bore three sons of Zeus (the Greek equivalent of Jupiter). The moon did not receive its present name until 1975;[7] before then, it was simply known as Jupiter VI or Jupiter Satellite VI, although calls for a full name appeared shortly after its and Elara's discovery; A.C.D. Crommelin wrote in 1905:
Unfortunately the numeration of Jupiter's satellites is now in precisely the same confusion as that of Saturn's system was before the numbers were abandoned and names substituted. A similar course would seem to be advisable here; the designation V for the inner satellite was tolerated for a time, as it was considered to be in a class by itself; but it has now got companions, so that this subterfuge disappears. The substitution of names for numerals is certainly more poetic.[8]
The moon was sometimes called Hestia, after the Greek goddess, from 1955 to 1975.[9]
[edit] Orbit
It is the largest member of the group that bears its name, the moons orbiting between 11.4 and 13 million kilometers from Jupiter at an inclination of about 27.5°.[10] The orbital elements are as of January 2000.[1] They are continuously changing due to Solar and planetary perturbations.
[edit] Physical characteristics
Himalia appears neutral (grey), like the other members of its group, with colour indices B-V=0.62, V-R= 0.4, similar to a C-type asteroid.[11] Measurements by Cassini confirm a featureless spectrum, with a slight absorption at 3 μm which could indicate the presence of water.[12]
[edit] Mass
In 2005, Emelyanov estimated Himalia to have a mass of 4.19 × 1018 kg (GM=0.28), based on a perturbation of Elara on July 15, 1949.[3] JPL's Solar System Dynamics assumes that Himalia has a mass of 6.7 × 1018 (GM=0.45) with a radius of 85 km.[2]
Himalia's density will depend on whether it has an average radius of about 67 km (geometric mean from Cassini 2000)[3] or a radius closer to 85 km.[2]
| Source | Radius km |
Density g/cm³ |
Mass kg |
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| Emelyanov | 67 | 3.33 | 4.19 × 1018 |
| Emelyanov | 85 | 1.63[4] | 4.19 × 1018 |
| JPL SSD | 85 | 2.6 | 6.7 × 1018 |
[edit] Exploration
In November 2000, the Cassini spacecraft, enroute to Saturn, made a number of images of Himalia, including photos from a distance as close as 4.4 million km. The moon covers only a few pixels, but seems to be an elongated object with axes 150 ± 20 and 120 ± 20 km, close to the Earth-based estimations.[5]
In February and March 2007, the New Horizons spacecraft to Pluto made a series of images of Himalia, culminating in photos from a distance of eight million km. Again, Himalia appears only a few pixels across.
[edit] See also
[edit] References
- ^ a b c d e Jacobson, R. A. (2000). "The orbits of outer Jovian satellites". Astronomical Journal 120: 2679–2686. doi:.
- ^ a b c d e f "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. http://ssd.jpl.nasa.gov/?sat_phys_par. Retrieved on 2008-12-11.
- ^ a b c d Emelyanov, N.V.; Archinal, B. A.; A’hearn, M. F.; et al. (2005). "The mass of Himalia from the perturbations on other satellites". Astronomy and Astrophysics 438: L33–L36. doi:.
- ^ a b Density = GM / G / (Volume of a sphere of 85km) = 1.63 g/cm³
- ^ a b Porco, Carolyn C.; et al. (March 2003). "Cassini Imaging of Jupiter's Atmosphere, Satellites, and Rings". Science 299: 1541–1547. doi:. PMID 12624258.
- ^ a b "Discovery of a Sixth Satellite of Jupiter". Astronomical Journal 24 (18): 154B. 1905. http://adsabs.harvard.edu//full/seri/AJ.../0024//0000154I002.html.;
"Sixth Satellite of Jupiter Confirmed (Himalaia)". Harvard College Observatory Bulletin 175: 1. 1905-01-25. http://adsabs.harvard.edu//full/seri/BHarO/0175//0000001.000.html.; Perrine, C.D. (1905). "Discovery of a Sixth Satellite to Jupiter". Publications of the Astronomical Society of the Pacific 17: 22–23. doi:. http://adsabs.harvard.edu//full/seri/PASP./0017//0000022.000.html.;
Perrine, C.D. (1905). "Orbits of the sixth and seventh satellites of Jupiter". Astronomische Nachrichten 169: 43–44. doi:. http://adsabs.harvard.edu//full/seri/AN.../0169//0000027.000.html. - ^ Marsden, B. G. (7 October 1974). "Satellites of Jupiter". IAUC Circular 2846. http://cfa-www.harvard.edu/iauc/02800/02846.html.
- ^ Crommelin, A. C. D. (March 10 1905)). "Provisional Elements of Jupiter's Satellite VI". Monthly Notices of the Royal Astronomical Society 65 (5): 524–527. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1905MNRAS..65..524C.
- ^ Payne-Gaposchkin, Cecilia; Katherine Haramundanis (1970). Introduction to Astronomy. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 0-134-78107-4.
- ^ a b Jewitt, David C.; Sheppard, Scott, and Porco, Carolyn (2004). "Jupiter’s Outer Satellites and Trojans". in Bagenal, F.; Dowling, T.E.; McKinnon, W.B. (pdf). Jupiter: The planet, Satellites and Magnetosphere. Cambridge University Press. http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP2003.pdf.
- ^ Rettig, Terrence W. (2001). "Implied Evolutionary Differences of the Jovian Irregular Satellites from a BVR Color Survey". Icarus 154: 313–320. doi:.
- ^ Chamberlain, Matthew A.; Brown, Robert H. (2004). "Near-infrared spectroscopy of Himalia". Icarus 172: 163–169. doi:.
[edit] External links
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