90482 Orcus

Orcus
90482 Orcus, provisional designation, is a trans-Neptunian object with a large moon, Vanth.wikipedia
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Michael E. Brown

Michael BrownMike BrownM. E. Brown
It was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004. Michael Brown's website lists Orcus as a dwarf planet with "near certainty", Tancredi concludes that it is one, and is massive enough to be considered one under the 2006 draft proposal of the IAU, but the IAU has not formally recognized it as such.
Particularly notable are Eris, a dwarf planet and the only TNO known to be more massive than Pluto, leading directly to Pluto's demotion from planet status; Sedna, a planetoid thought to be the first observed body of the inner Öpik–Oort cloud; and Orcus.

David L. Rabinowitz

D. L. RabinowitzDavid RabinowitzD. Rabinowitz
It was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.
Collaborating with Michael Brown and Chad Trujillo of the Quasar Equatorial Survey Team, he has participated in the discovery of several plutoids such as 90377 Sedna (possibly the first known inner Oort cloud object), 90482 Orcus, Eris (more massive than Pluto ), and, although he would not get credit for Haumea.

Trans-Neptunian object

TNOtrans-Neptunian objectscolor indices
90482 Orcus, provisional designation, is a trans-Neptunian object with a large moon, Vanth.
A recent attempt at classification (common with centaurs) uses the total of four classes from BB (blue, average B−V = 0.70, V−R = 0.39, e.g. Orcus) to RR (very red, B−V = 1.08, V−R = 0.71, e.g. Sedna) with BR and IR as intermediate classes.

List of possible dwarf planets

dwarf planet candidatepossible dwarf planetdwarf-planet candidate
With a diameter of 910 km, it is a possible dwarf planet.
Grundy et al. propose therefore that mid-size, low-density and low-albedo (< ≈0.2) bodies such as Salacia, Varda, Gǃkúnǁʼhòmdímà and are not differentiated planetary bodies like Orcus, Quaoar and Charon.

Chad Trujillo

C. TrujilloC. A. TrujilloChadwick A. Trujillo
It was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.

Plutino

plutinos2:3 resonance with Neptune2:3 resonant
Orcus is a plutino, a trans-Neptunian object that is locked in a 2:3 resonance with the ice giant Neptune, making two revolutions around the Sun to every three of Neptune's. Orcus is in a 2:3 orbital resonance with Neptune, having an orbital period of 246 years, and is classified as a plutino.

Orcus

Orcosorcies
This was a major consideration in selecting its name, as the deity Orcus was the Etruscan equivalent of the Roman Pluto, and later became an alternate name for Pluto.
The Kuiper belt object 90482 Orcus is named after Orcus.

IAU definition of planet

2006 definition of planetdefinition of a planetdefinition of planet
Michael Brown's website lists Orcus as a dwarf planet with "near certainty", Tancredi concludes that it is one, and is massive enough to be considered one under the 2006 draft proposal of the IAU, but the IAU has not formally recognized it as such.
Such a definition of the term "planet" could also have led to changes in classification for the trans-Neptunian objects,, Sedna, Orcus, Quaoar, Varuna,, Ixion, and, and the asteroids Vesta, Pallas, and Hygiea.

Precovery

precoveriesprecoveredPrediscovery
Precovery images taken by the Palomar Observatory as early as 8 November 1951 were later obtained from the Digitized Sky Survey.

Astronomical naming conventions

formally designatednaming conventionalso written
Under the guidelines of the International Astronomical Union's (IAU) naming conventions, objects with a similar size and orbit to that of Pluto are named after underworld deities.

50000 Quaoar

Quaoar
The 1.65 μm band on Orcus is broad and deep (12%), as on Charon, Quaoar, Haumea, and icy satellites of giant planets.
A 2006 model of internal heating via radioactive decay suggested that, unlike 90482 Orcus, Quaoar may not be capable of sustaining an internal ocean of liquid water at the mantle–core boundary.

Vanth

winged female demon
On 30 March 2005, Orcus's moon, Vanth, was named after a winged female demon of the Etruscan underworld.
* Vanth (moon), moon of Orcus

Orbital resonance

1:1 resonanceresonancemean-motion resonance
Orcus is in a 2:3 orbital resonance with Neptune, having an orbital period of 246 years, and is classified as a plutino.
The next largest body in a similar 2:3 resonance with Neptune, called a plutino, is the probable dwarf planet Orcus.

Ocean

marineoceansmaritime
Models of internal heating via radioactive decay suggest that Orcus may be capable of sustaining an internal ocean of liquid water.
Not enough is known of the larger trans-Neptunian objects to determine whether they are differentiated bodies capable of supporting oceans, although models of radioactive decay suggest that Pluto, Eris, Sedna, and Orcus have oceans beneath solid icy crusts approximately 100 to 180 km thick.

Minor-planet moon

moonasteroid moonbinary
90482 Orcus, provisional designation, is a trans-Neptunian object with a large moon, Vanth.

Vanth (moon)

VanthOrcus I Vanth1
90482 Orcus, provisional designation, is a trans-Neptunian object with a large moon, Vanth.

Dwarf planet

dwarf planetsList of dwarf planetsplanet
With a diameter of 910 km, it is a possible dwarf planet. Michael Brown's website lists Orcus as a dwarf planet with "near certainty", Tancredi concludes that it is one, and is massive enough to be considered one under the 2006 draft proposal of the IAU, but the IAU has not formally recognized it as such.

Methane

methane gasCH 4 liquid methane
Other compounds like methane or ammonia may also be present on its surface.

Ammonia

NH 3 anhydrous ammonialiquid ammonia
Other compounds like methane or ammonia may also be present on its surface.

Neptune

NeptunianAtmosphere of NeptuneNeptune-mass
Orcus is a plutino, a trans-Neptunian object that is locked in a 2:3 resonance with the ice giant Neptune, making two revolutions around the Sun to every three of Neptune's. Orcus is in a 2:3 orbital resonance with Neptune, having an orbital period of 246 years, and is classified as a plutino.

Pluto

134340 Pluto(134340) Plutoescaped moon of Neptune
Under the guidelines of the International Astronomical Union's (IAU) naming conventions, objects with a similar size and orbit to that of Pluto are named after underworld deities. This is much like Pluto, except that the phase of Orcus's orbit is opposite from Pluto's: Orcus is at aphelion when Pluto is at perihelion and vice versa.

Phase (waves)

phasephase shiftout of phase
This is much like Pluto, except that the phase of Orcus's orbit is opposite from Pluto's: Orcus is at aphelion when Pluto is at perihelion and vice versa.

Apsis

perigeeperihelionapogee
This is much like Pluto, except that the phase of Orcus's orbit is opposite from Pluto's: Orcus is at aphelion when Pluto is at perihelion and vice versa.

Charon (moon)

CharonPluto I Charon(134340) Pluto I Charon
The 1.65 μm band on Orcus is broad and deep (12%), as on Charon, Quaoar, Haumea, and icy satellites of giant planets. Because of these similarities and contrasts, along with its large moon Vanth that recalls Pluto's large moon Charon, Orcus has been regarded as the anti-Pluto.