Himalia as seen by Cassini–Huygens
|Discovered by||C. D. Perrine|
|Discovery date||December 3, 1904|
|Mean orbit radius||11,460,000 km|
|Orbital period||250.56 d (0.704 a)|
|Average orbital speed||3.312 km/s|
|Mean radius||85 ± ?? km|
|Surface area||~90,800 km2|
|Mean density||2.6 g/cm3 (assumed)
1.63 g/cm3 (assuming radius 85 km)
|Equatorial surface gravity||~0.062 m/s2 (0.006 g)|
|Escape velocity||~0.100 km/s|
|Sidereal rotation period||7.782 h|
Himalia (// hy-MAY-lee-ə or // hi-MAH-lee-ə; Greek: ‘Ιμαλíα) is the largest irregular satellite of Jupiter, the sixth largest overall in size, and only the four Galilean moons of Jupiter have greater mass. It was discovered by Charles Dillon Perrine at the Lick Observatory on 3 December 1904 and is named after the nymph Himalia, who bore three sons of Zeus (the Greek equivalent of Jupiter).
Himalia, the largest irregular satellite of Jupiter, was discovered by Charles Dillon Perrine at the Lick Observatory on 3 December 1904. Himalia is Jupiter's most easily-observed small satellite; though Amalthea is brighter, its proximity to the planet's brilliant disk makes it a far more difficult object to view.
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; 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.
At a distance of about 11.5 million km from Jupiter, Himalia takes about 251 Earth days to complete one 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°. The orbital elements are as of January 2000. They are continuously changing due to solar and planetary perturbations.
Himalia's rotational period is 7 h 46 m 55±2 s. Himalia appears neutral in color (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. Measurements by Cassini confirm a featureless spectrum, with a slight absorption at 3 μm which could indicate the presence of water.
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. JPL's Solar System dynamics web site assumes that Himalia has a mass of 6.7×1018 kg (GM=0.45) with a radius of 85 km.
In November 2000, the Cassini spacecraft, en route 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.
In February and March 2007, the New Horizons spacecraft en route 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.
Possible relationship with Jupiter's rings
The small moon S/2000 J 11, 4 kilometres in diameter, had gone missing since its discovery in 2000. One theory was that it had crashed into the much larger moon Himalia, 170 kilometres in diameter, creating a faint ring. This possible ring appears as a faint streak near Himalia in images from NASA's New Horizons mission to Pluto. This suggests that Jupiter sometimes gains and loses small moons through collisions. However, the recovery of S/2000 J 11 in 2010 and 2011 disproves the link between S/2000 J 11 and the Himalia ring, although it is still possible that a different moon may have been involved.
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- "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-11.
- 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 (3): L33–L36. Bibcode:2005A&A...438L..33E. doi:10.1051/0004-6361:200500143.
- Density = GM / G / (Volume of a sphere of 85km) = 1.63 g/cm3
- Pilcher, Frederick; Mottola, Stefano; Denk, Tilmann (2012). "Photometric lightcurve and rotation period of Himalia (Jupiter VI)". Icarus 219 (2): 741–742. Bibcode:2012Icar..219..741P. doi:10.1016/j.icarus.2012.03.021.
- Porco, Carolyn C.; et al. (March 2003). "Cassini Imaging of Jupiter's Atmosphere, Satellites, and Rings". Science 299 (5612): 1541–1547. Bibcode:2003Sci...299.1541P. doi:10.1126/science.1079462. PMID 12624258.
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- Payne-Gaposchkin, Cecilia; Katherine Haramundanis (1970). Introduction to Astronomy. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 0-13-478107-4.
- "Himalia Facts". NASA. NASA. Retrieved 25 May 2011.
- Jewitt, David C.; Sheppard, Scott, and Porco, Carolyn (2004). "Jupiter’s Outer Satellites and Trojans" (PDF). In Bagenal, F.; Dowling, T.E.; McKinnon, W.B. Jupiter: The planet, Satellites and Magnetosphere. Cambridge University Press.
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- Chamberlain, Matthew A.; Brown, Robert H. (2004). "Near-infrared spectroscopy of Himalia". Icarus 172 (1): 163–169. Bibcode:2004Icar..172..163C. doi:10.1016/j.icarus.2003.12.016.
- IAUC 7555, January 2001. "FAQ: Why don't you have Jovian satellite S/2000 J11 in your system?". JPL Solar System Dynamics. Retrieved 2011-02-13.
- "Lunar marriage may have given Jupiter a ring", New Scientist, March 20, 2010, p. 16.
- Gareth V. Williams (2012-09-11). "MPEC 2012-R22 : S/2000 J 11". Minor Planet Center. Retrieved 2012-09-11.
- Himalia Profile by NASA's Solar System Exploration
- David Jewitt pages
- Jupiter's Known Satellites (by Scott S. Sheppard)
- Two Irregular Satellites of Jupiter (Himalia & Elara : Remanzacco Observatory : November 23, 2012)