Orcus (dwarf planet)

For the Roman god, see Orcus (mythology). For other uses, see Orcus (disambiguation).

90482 Orcus
Orcus and its moon Vanth imaged by the Hubble Space Telescope in 2006
Discovery[1][2]
Discovered by
Discovery date17 February 2004
Designations
(90482) Orcus
Pronunciation/ˈɔːrkəs/[3]
Named after
Orcus[4]
2004 DW
AdjectivesOrcean /ˈɔːrsiən/[8]
Symbol🝿
Orbital characteristics[1]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 2
Observation arc68.16 yr (24,894 days)
Earliest precovery date8 November 1951
Aphelion48.067 AU (7.1907 Tm)
Perihelion30.281 AU (4.5300 Tm)
39.174 AU (5.8603 Tm)
Eccentricity0.22701
245.19 yr (89,557 days)
181.735°
0° 0m 14.472s / day
Inclination20.592°
268.799°
≈ 10 January 2143[9]
±1 day
72.310°
Known satellites1 (Vanth)
Physical characteristics
Dimensions910+50
−40 km[10] 917±25 km[11]
Mass(6.348±0.019)×1020 kg (Orcus and Vanth combined)[7]
(5.47±0.10)×1020 kg (Orcus only)[a]
Mean density
1.4±0.2 g/cm3[12]
Equatorial surface gravity
≈ 0.2 m/s2
Equatorial escape velocity
≈ 0.43 km/s
0.231+0.018
−0.011[11]
Temperature< 44 K[13]
(neutral)[13]
B–V =0.68[14]
V–R = 0.37[14]
19.1 (opposition)[15]
2.31±0.03 (integral),[11] 2.41±0.05[16]

Orcus (minor-planet designation: 90482 Orcus) is a dwarf planet located in the Kuiper belt, with one large moon, Vanth.[7] It has an estimated diameter of 870 to 960 km (540 to 600 mi), comparable to the Inner Solar System dwarf planet Ceres. The surface of Orcus is relatively bright with albedo reaching 23 percent, neutral in color, and rich in water ice. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Other compounds like methane or ammonia may also be present on its surface. Orcus was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.

Orcus is a plutino, a trans-Neptunian object that is locked in a 2:3 orbital resonance with the ice giant Neptune, making two revolutions around the Sun to every three of Neptune's.[5] This is much like Pluto, except that the phase of Orcus's orbit is opposite to Pluto's: Orcus is at aphelion (most recently in 2019) around when Pluto is at perihelion (most recently in 1989) and vice versa.[17] Orcus is the second-largest known plutino, after Pluto itself. The perihelion of Orcus's orbit is around 120° from that of Pluto, while the eccentricities and inclinations are similar. Because of these similarities and contrasts, along with its large moon Vanth that can be compared to Pluto's large moon Charon, Orcus has been dubbed the "anti-Pluto."[18] This was a major consideration in selecting its name, as the deity Orcus was the Roman/Etruscan equivalent of the Roman/Greek Pluto.[18]

  1. ^ a b c Cite error: The named reference jpldata was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference MPC-Orcus was invoked but never defined (see the help page).
  3. ^ "Orcus". Dictionary.com Unabridged (Online). n.d.
  4. ^ Cite error: The named reference springer was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Buie was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference MPEC 2009-E53 was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference Grundy-orbits was invoked but never defined (see the help page).
  8. ^ Angley (1847) De Clifford, the philosopher
  9. ^ Cite error: The named reference Horizons2143 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference brown2018 was invoked but never defined (see the help page).
  11. ^ a b c Cite error: The named reference TNOsCool8 was invoked but never defined (see the help page).
  12. ^ a b Cite error: The named reference Brown2023 was invoked but never defined (see the help page).
  13. ^ a b Cite error: The named reference Barucci2008 was invoked but never defined (see the help page).
  14. ^ a b Cite error: The named reference deBergh2005 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Horizons was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Brown2010 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference MPC2004-D15 was invoked but never defined (see the help page).
  18. ^ a b Cite error: The named reference MBP was invoked but never defined (see the help page).


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