![]() Orcus and its moon Vanth imaged by the Hubble Space Telescope in 2006 | |
Discovery[1][2] | |
---|---|
Discovered by | M. E. Brown C. Trujillo D. Rabinowitz |
Discovery date | 17 February 2004 |
Designations | |
(90482) Orcus | |
Pronunciation | /ˈɔːrkəs/[3] |
Named after | Orcus (Roman mythology)[4] |
2004 DW | |
TNO[1] · plutino[5][6] dwarf planet[7] | |
Adjectives | Orcean /ˈɔːrsiən/[8] |
Symbol | ![]() |
Orbital characteristics[1] | |
Epoch 31 May 2020 (JD 2459000.5) | |
Uncertainty parameter 2 | |
Observation arc | 68.16 yr (24,894 days) |
Earliest precovery date | 8 November 1951 |
Aphelion | 48.067 AU (7.1907 Tm) |
Perihelion | 30.281 AU (4.5300 Tm) |
39.174 AU (5.8603 Tm) | |
Eccentricity | 0.22701 |
245.19 yr (89,557 days) | |
181.735° | |
0° 0m 14.472s / day | |
Inclination | 20.592° |
268.799° | |
≈ 10 January 2143[9] ±1 day | |
72.310° | |
Known satellites | 1 (Vanth) |
Physical characteristics | |
Dimensions | 910+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]
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