Quaoar
- This article is about the trans-Neptunian object. For the Tongva god, see Quaoar (deity).
50000 Quaoar (/"kwA o Ar/) is a Trans-Neptunian object orbiting the Sun in the Edgeworth-Kuiper belt. It was discovered on June 4, 2002 by astronomers Chad Trujillo and Mike Brown at the California Institute of Technology in Pasadena, California from images acquired by Palomar Observatory using the JPL Near Earth Asteroid Tracking program. This discovery was announced on October 7 2002, at a meeting of the American Astronomical Society.
Quaoar is estimated to have a diameter of about 1,200 kilometres, which at the time of discovery made it the largest object found in the solar system since Pluto and, indeed, the largest known minor planet (although the newly discovered (2003 VB12) Sedna and 2004 DW may turn out to be bigger). More massive than all of the asteroids put together, it is about one tenth the diameter of Earth or one third the diameter of the Moon. It orbits at about 6 billion kilometres from the Sun with an orbital period of 286 years.
The planetoid's name follows International Astronomical Union rules by naming all planetoids after creation deities (see planetary nomenclature). "Quaoar" is the name of a creation deity of the Native American Tongva people, native to the area around Los Angeles, where the discovery was named. The IAU approved the name Quaoar, making it the official name; it also has the systematic name 2002 LM60 and the minor planet number 50000.
The discovery weakens Pluto's case to be classed as a planet, since astronomers expect that there may be as many as a dozen Kuiper Belt objects the size of Quaoar. Or it may require a change to the definition of planet to include Pluto, Quaoar, and Sedna. A more recent discovery, Sedna, is even larger than Quaoar. Some expect to find planetoids larger than Pluto. In some ways, Quaoar has more claim to be a planet than Pluto does: it has a more typical planetary orbit (a near-circular orbit with a radius of somewhat over 40 AU rather than a highly eccentric one like Pluto).
Quaoar is believed to be a mixture of rock and ice, like other Kuiper Belt Objects; however its extremely low albedo (estimated at 0.1) indicates that the ice has disappeared from its outer layers. After the New Horizons mission visits Pluto (in 2015) and goes on to visit several Kuiper Belt Objects our knowledge of such things should greatly improve.
