Himalia (moon)

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° 26m 59.616s / 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 km2
Volume	~ 2600000 km3
Mass	(4.2±0.6)×1018 kg[9]
Mean density	2.6 g/cm3 (assumed)[7] 1.63 g/cm3 (assuming radius 85 km)[9][a]
Surface gravity	~ 0.062 m/s2 (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]

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.^[b]

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]

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]

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

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]

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]

• 1. ^ ^{a b} 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. ^ ^{a b c} 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. ^ ^{a b} "M.P.C. 115889" (PDF). Minor Planet Circular. Minor Planet Center. 27 August 2019. Retrieved 27 February 2020.
  5. ^ ^{a b c d e} 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. ^ ^{a b c d e} 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. ^ ^{a b c d e f g} "Planetary Satellite Physical Parameters". JPL (Solar System Dynamics). 2008-10-24. Retrieved 2008-12-11.
  8. ^ ^{a b} 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. ^ ^{a b c d} 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. ^ ^{a b c} 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)