Vanth (moon)

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Discovered by Mike Brown and T.-A. Suer
Discovery date 13 November 2005
Pronunciation /ˈvænθ/
S/2005 (90482) 1,
Orcus I
Adjectives Vanthian
Orbital characteristics[1]
9030 ± 89 km
Eccentricity 0.007 ± 0.003
9.5406 ± 0.0004 days
Inclination ±21°
Satellite of Orcus
Physical characteristics
Dimensions 378±100 km
(Vanth's albedo of 0.12)[1]
276±17 km
(assuming equal albedos)[2]
Mass 2–6 × 1019 kg
Mean density
≈ 1.5 g/cm3
≈ 0.11 m/s2
≈ 0.447 km/s
Albedo ≈ 0.12[1]
Spectral type
moderately red (optical)[4]
21.97 ± 0.05[4]
4.88 ± 0.05[4]

Vanth, officially (90482) Orcus I Vanth, is the single known natural satellite of the plutino and likely dwarf planet Orcus. It was discovered by Mike Brown and T.-A. Suer using discovery images taken by the Hubble Space Telescope on November 13, 2005.[5] The discovery was announced on 22 February 2007 in IAUC 8812.[6]


The moon orbits Orcus "in a tight precise circle", with a period of approximately 10 days.[7] Brown suspects that, like Pluto and Charon, Orcus and Vanth are tidally locked.[7]


Vanth was found at 0.25 arcsec from Orcus with magnitude difference of 2.7±1.0.[5] Estimates made in 2009 by Mike Brown show that the apparent magnitude of Vanth is 21.97±0.05 which is 2.54±0.01 magnitudes fainter than Orcus.[4] Assuming equal albedos this would mean a diameter of 280 km, or 2.9 times smaller than the primary.[1] However, the dissimilar colors of Orcus (neutral) and Vanth (red) suggest that Vanth could have an albedo a factor of two lower than Orcus.[4] Should Vanth have an albedo of only 0.12, Vanth could be as large as 380 km with Orcus being 760 km in diameter.[1] The mass of Vanth also depends on its albedo and can vary from 3 to 9% of the total system mass.[1][4]

The satellite does not resemble other known collisional satellites because its spectrum is very different of that of its primary. Vanth may thus be a captured Kuiper belt object.[7]


Upon discovery, Vanth was issued a provisional designation, S/2005 (90482) 1. On March 23, 2009, Brown asked readers of his weekly column to suggest possible names for the satellite, with the best one to be submitted to the International Astronomical Union (IAU) on April 5.[7] The name Vanth, the winged Etruscan psychopomp who guides the souls of the dead to the underworld, was chosen from among a large pool of submissions. Vanth was the only suggestion that was purely Etruscan in origin. It was the most popular submission, first suggested by Sonya Taaffe.[8] This submission was assessed and approved by the IAU's Committee for Small Body Nomenclature in their March 30, 2010 circular.[9]

The Etruscan Vanth is frequently portrayed in the company of Charun (Charon), and so as the name of the moon of Orcus (nicknamed the "anti-Pluto" because resonance with Neptune keeps it on the opposite side of the Sun from Pluto), it is an allusion to the parallels between Orcus and Pluto. Brown quoted Taaffe as saying that if Vanth "accompanies dead souls from the moment of death to the underworld itself, then of course her face is turned always toward Orcus", a reference to the likely synchronous orbit of Vanth about Orcus.[8]

See also[edit]


  1. ^ a b c d e f Carry, B.; Hestroffer, D.; Demeo, F. E.; Thirouin, A.; Berthier, J.; Lacerda, P.; Sicardy, B.; Doressoundiram, A.; Dumas, C.; Farrelly, D.; Müller, T. G. (2011). "Integral-field spectroscopy of (90482) Orcus-Vanth". Astronomy & Astrophysics. 534: A115. arXiv:1108.5963free to read. Bibcode:2011A&A...534A.115C. doi:10.1051/0004-6361/201117486. 
  2. ^ Fornasier,, S.; Lellouch,, E.; Müller, P., T.; et .al. (2013). "TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of 9 bright targets at 70–500 µm.". Astronomy & Astrophysics. 555: A92. arXiv:1305.0449v2free to read. Bibcode:2013A&A...555A..15F. doi:10.1051/0004-6361/201321329. 
  3. ^ Ortiz, J. L.; Cikota, A.; Cikota, S.; Hestroffer, D.; Thirouin, A.; Morales, N.; Duffard, R.; Gil-Hutton, R.; Santos-Sanz, P.; De La Cueva, I. (2010). "A mid-term astrometric and photometric study of trans-Neptunian object (90482) Orcus". Astronomy & Astrophysics. 525: A31. arXiv:1010.6187free to read. Bibcode:2011A&A...525A..31O. doi:10.1051/0004-6361/201015309. 
  4. ^ a b c d e f Brown, M.E.; Ragozzine, D.; Stansberry, J.; Fraser, W.C. (2010). "The size, density, and formation of the Orcus-Vanth system in the Kuiper belt". The Astronomical Journal. 139 (6): 2700–2705. arXiv:0910.4784free to read. Bibcode:2010AJ....139.2700B. doi:10.1088/0004-6256/139/6/2700. 
  5. ^ a b Daniel W. E. Green (2007-02-22). "IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637),, (90482)". International Astronomical Union Circular. Retrieved 2011-07-04. 
  6. ^ Wm. Robert Johnston (2007-03-04). "(90482) Orcus". Johnston's Archive. Retrieved 2009-03-26. 
  7. ^ a b c d Michael E. Brown (2009-03-23). "S/1 90482 (2005) needs your help". Mike Brown's Planets (blog). Retrieved 2009-03-25. 
  8. ^ a b Michael E. Brown (2009-04-06). "Orcus Porcus". Mike Brown's Planets (blog). Retrieved 2009-04-06. 
  9. ^ "Minor planet circular" (PDF). 2010. Retrieved 2010-08-08.