Himalia (moon)

Himalia /hɪˈmeɪliə/, or Jupiter VI, is the largest irregular satellite of Jupiter, with a diameter of at least 140 km (90 mi).[5] It is the fifth largest Jovian satellite, after the four Galilean moons. 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).[1] It is one of the largest planetary moons in the Solar System not imaged in detail, and the largest within the orbit of Neptune.[lower-alpha 2]

This article is about Jupiter's irregular moon. For the mythological figure, see Himalia (mythology).

Himalia

Himalia as seen by spacecraft Cassini
Discovery [1]
Discovered by	Charles D. Perrine
Discovery site	Lick Observatory
Discovery date	3 December 1904
Designations
Designation	Jupiter VI
Pronunciation	/hɪˈmeɪliə/ or /hɪˈmɑːliə/[2]
Named after	Ἱμαλία Himalia
Adjectives	Himalian[3]
Orbital characteristics [4]
Epoch 27 April 2019 (JD 2458600.5)
Observation arc	114.32 yr (41,728 d)
Semi-major axis	0.0761287 AU (11,388,690 km)
Eccentricity	0.1537860
Orbital period	+248.29 d
Average orbital speed	3.312 km/s
Mean anomaly	94.30785°
Mean motion	1° 26^m 59.616^s / day
Inclination	29.90917° (to the ecliptic)
Longitude of ascending node	44.99935°
Argument of perihelion	21.60643°
Satellite of	Jupiter
Group	Himalia group
Physical characteristics
Dimensions	205.6 × 141.4 km (occultation, projected)[5] 150±20 × 120±20 km (Cassini estimate)[6]
Mean diameter	170 km (ground-based estimate)[7][6] 139.6±1.7 km[8]
Surface area	~ 91000 km^2
Volume	~ 2600000 km^3
Mass	(4.2±0.6)×10^18 kg[9]
Mean density	2.6 g/cm^3 (assumed)[7] 1.63 g/cm^3 (assuming radius 85 km)[9][lower-alpha 1]
Surface gravity	~ 0.062 m/s^2 (0.006 g)
Escape velocity	~ 0.100 km/s
Rotation period	7.7819±0.0005 h[10]
Albedo	0.057±0.008[8] 0.04[7][6]
Temperature	~ 124 K
Apparent magnitude	14.6[7]
Absolute magnitude (H)	7.9[4]

Discovery

Himalia was discovered by Charles Dillon Perrine at the Lick Observatory on 3 December 1904.[1] 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.[11][12]

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;[13] 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 [Amalthea] 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.[14]

The moon was sometimes called Hestia, after the Greek goddess, from 1955 to 1975.[15]

Orbit

Animation of Himalia's orbit.
   Jupiter ·    Himalia ·   Callisto

At a distance of about 11,400,000 km (7,100,000 mi) from Jupiter, Himalia takes about 250 Earth days to complete one orbit around Jupiter.[16] It is the largest member of the Himalia group, which are a group of small moons orbiting Jupiter at a distance from 11,400,000 km (7,100,000 mi) to 13,000,000 km (8,100,000 mi), with inclined orbits at an angle of 27.5 degrees to Jupiter's equator.[17] Their orbits are continuously changing due to solar and planetary perturbations.[18]

Physical characteristics

Himalia's rotational light curve from Earth-based observations taken between August and October 2010.[10]

Himalia observed by the Wide-field Infrared Survey Explorer (WISE) spacecraft in 2014

Himalia's rotational period is 7 h 46 m 55±2 s.[10] 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.[19] Measurements by Cassini confirm a featureless spectrum, with a slight absorption at 3 μm, which could indicate the presence of water.[20]

Resolved images of Himalia by Cassini have led to a size estimate of 150 km × 120 km (93 mi × 75 mi), while ground-based estimates suggest that Himalia is large, with a diameter around 170 km (110 mi).[6][7] In May 2018, Himalia occulted a star, allowing for precise measurements of its size.[5] The occultation was observed from the US state of Georgia.[5] From the occultation, Himalia was given a size estimate of 205.6 km × 141.3 km (127.8 mi × 87.8 mi), in agreement with earlier ground-based estimates.[5]

Mass

In 2005, Emelyanov estimated Himalia to have a mass of (4.2±0.6)×10¹⁸ kg (GM=0.28±0.04), based on a perturbation of Elara on July 15, 1949.[9] 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.[7]

Himalia's density will depend on whether it has an average radius of about 67 km (geometric mean from Cassini)[9] or a radius closer to 85 km.[7]

Cassini image of Himalia, taken in December 2000 from a distance of 4.4 million kilometres

Source	Radius km	Density g/cm³	Mass kg
Emelyanov	67	3.33	4.2×10^18
Emelyanov	85	1.63[lower-alpha 1]	4.2×10^18
JPL SSD	85	2.6	6.7×10^18

Exploration

Phases of Himalia imaged by the LORRI instrument aboard New Horizons

In November 2000, the Cassini spacecraft, en route to Saturn, made a number of images of Himalia, including photos from a distance of 4.4 million km. Himalia 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.[6]

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 8 million km. Again, Himalia appears only a few pixels across.[21]

Possible relationship with Jupiter's rings

New Horizons image of possible Himalia ring

The small moon Dia, 4 kilometres in diameter, had gone missing since its discovery in 2000.[22] 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.[23] However, the recovery of Dia in 2010 and 2011[24] disproves the link between Dia and the Himalia ring, although it is still possible that a different moon may have been involved since an impact by an object the size of Dia would produce far more material than the predicted lower limit volume of ejected material.[25]

See also

• Irregular satellites

Notes

1. Density = GM / G / (Volume of a sphere of 85km) = 1.63 g/cm³
2. It is the largest with the exception of some of the moons of Neptune and several trans-Neptunian objects, particularly Dysnomia, the moon of Eris.

References

1. Porter, J.G. (1905). "Discovery of a Sixth Satellite of Jupiter". Astronomical Journal. 24 (18): 154B. Bibcode:1905AJ.....24..154P. doi:10.1086/103612.;
   Perrine, C.D. (1905-01-25). "Sixth Satellite of Jupiter Confirmed". Harvard College Observatory Bulletin. 175: 1. Bibcode:1905BHarO.175....1P.;
   Perrine, C.D. (1905). "Discovery of a Sixth Satellite to Jupiter". Publications of the Astronomical Society of the Pacific. 17 (100): 22–23. Bibcode:1905PASP...17...22.. doi:10.1086/121619.;
   Perrine, C.D. (1905). "Orbits of the sixth and seventh satellites of Jupiter" (PDF). Astronomische Nachrichten. 169 (3): 43–44. Bibcode:1905AN....169...43P. doi:10.1002/asna.19051690304.
2. Daintith & Gould (2006) The Facts on File Dictionary of Astronomy, p. 216
3. Yenne (1987) The Atlas of the Solar System.
4. "M.P.C. 115889" (PDF). Minor Planet Circular. Minor Planet Center. 27 August 2019. Retrieved 27 February 2020.
5. N. Smith; R. Venable (12 May 2018). "Jupiter (06) Himalia". www.asteroidoccultation.com. Archived from the original on 24 July 2018. Retrieved 23 July 2018.
6. 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.
7. "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-11.
8. Grav, T.; Bauer, J. M.; Mainzer, A. K.; Masiero, J. R.; Nugent, C. R.; Cutri, R. M.; et al. (August 2015). "NEOWISE: Observations of the Irregular Satellites of Jupiter and Saturn". The Astrophysical Journal. 809 (1): 9. Bibcode:2015ApJ...809....3G. doi:10.1088/0004-637X/809/1/3. 3.
9. Emelyanov, N.V. (2005). "The mass of Himalia from the perturbations on other satellites" (PDF). Astronomy and Astrophysics. 438 (3): L33–L36. Bibcode:2005A&A...438L..33E. doi:10.1051/0004-6361:200500143.
10. 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.
11. "Himalia, Jupiter's "fifth" moon". October 2009. Archived from the original on July 19, 2011.
12. Rick Scott (October 20, 2003). "Finding Himalia, The Fifth Brightest Moon Of Jupiter". Astronomy.net. Retrieved 2011-11-07.
13. Marsden, B. G. (7 October 1975). "IAUC 2846: N Mon 1975 (= A0620-00); N Cyg 1975; 1975h; 1975g; 1975i; Sats OF JUPITER". Central Bureau for Astronomical Telegrams. IAU. Retrieved 2018-09-09.
14. 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. Bibcode:1905MNRAS..65..524C. doi:10.1093/mnras/65.5.524.
15. Payne-Gaposchkin, Cecilia; Katherine Haramundanis (1970). Introduction to Astronomy. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 978-0-13-478107-5.
16. "Himalia". Solar System Exploration. NASA. December 5, 2017. Retrieved 2018-09-09.
17. Jewitt, David C.; Sheppard, Scott & Porco, Carolyn (2004). "Jupiter's Outer Satellites and Trojans" (PDF). In Bagenal, F.; Dowling, T. E. & McKinnon, W. B. (eds.). Jupiter: The planet, Satellites and Magnetosphere. Cambridge University Press.
18. Jacobson, R. A. (2000). "The orbits of outer Jovian satellites" (PDF). Astronomical Journal. 120 (5): 2679–2686. Bibcode:2000AJ....120.2679J. doi:10.1086/316817.
19. Rettig, T. W.; Walsh, K.; Consolmagno, G. (December 2001). "Implied Evolutionary Differences of the Jovian Irregular Satellites from a BVR Color Survey". Icarus. 154 (2): 313–320. Bibcode:2001Icar..154..313R. doi:10.1006/icar.2001.6715.CS1 maint: ref=harv (link)
20. 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.
21. Lakdawalla, E. (1 March 2007). "The Bruce Murray Space Image Library - Jupiter's moon Himalia". Retrieved 17 November 2018.
22. "Long Lost Moon of Jupiter Found". Carnegie Science | DTM. May 13, 2013. Retrieved 2018-09-09.
23. "Lunar marriage may have given Jupiter a ring". New Scientist. March 20, 2010. p. 16.
24. Gareth V. Williams (2012-09-11). "MPEC 2012-R22 : S/2000 J 11". Minor Planet Center. Archived from the original on 2014-08-21. Retrieved 2012-09-11.
25. Cheng, A. F.; Weaver, H. A.; Nguyen, L.; Hamilton, D. P.; Stern, S. A.; Throop, H. B. (March 2010). A New Ring or Ring Arc of Jupiter? (PDF). 41st Lunar and Planetary Science Conference. Lunar and Planetary Institute. p. 2549. Bibcode:2010LPI....41.2549C.

External links

• "Himalia: Overview" 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)