Orcus (minor planet 90482)
One of the largest known Kuiper Belt
objects (KBO). It was initially and provisionally known as 2004 DW.
The name Orcus, from a Roman god of the dead and another name for the Greek
deity Hades, was approved by the International Astronomical Union (IAU)
on Nov. 22, 2004. It was chosen because Orcus moves in an orbit similar
to that of Pluto
| Orbits of Orcus (red), Pluto (green),
and other planets compared
Orcus was discovered in images taken on Feb. 17, 2004 (nearly 74 years to
the day after Pluto was found) by Mike Brown
(CalTech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale)
– the same team that discovered the largest known KBO, Eris
(formerly called 2003 UB313). The diameter of Orcus has been put at about
1,600 km (compared with Pluto's 2,300 km) but this is only an estimate because
of uncertainty in the object's albedo (relectivity).
Orcus moves in an orbit similar to that of Pluto, i.e. it completes three
orbits of the Sun for every two of Neptune goes around the sun. It is therefore
classified as a plutino.
Under new guidelines being considered by astronomers for what constitutes
a planet, Orcus may be elevated to the status of a dwarf
planet if it turns out that its shape is approximately spherical.
| Discovery images of Orcus.
Credit: Vrown, Rabinowitz, and Trujillo
known Kuiper Belt objects
ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS