page_title: 90482 Orcus
section_title: Discovery
hierarchical_section_title: 90482 Orcus / History / Discovery
caption_attribution_description: English: 90482 Orcus. The location of Orcus is shown in the green circle (top, left). Courtesy of NASA
context_page_description: 90482 Orcus, provisional designation 2004 DW, is a trans-Neptunian object with a large moon, Vanth. With a diameter of 910 km, it is a possible dwarf planet. 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. It 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 resonance with the ice giant Neptune, making two revolutions around the Sun to every three of Neptune's. 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. Moreover, the aphelion of Orcus's orbit points in nearly the opposite direction from Pluto's, although the eccentricities and inclinations are similar.
context_section_description: Orcus was discovered on 17 February 2004, by American astronomers Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University. Precovery images taken by the Palomar Observatory as early as 8 November 1951 were later obtained from the Digitized Sky Survey.
caption: Discovery image of Orcus taken in 2004[18]
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