Quaoar

Lore & Background

Quaoar was discovered on 4 June 2002 by American astronomers Chad Trujillo and Michael Brown at the Palomar Observatory in the Palomar Mountain Range in San Diego County, California. The discovery formed part of the Caltech Wide Area Sky Survey, which was designed to search for the brightest Kuiper belt objects using the Palomar Observatory's 1.22-meter Samuel Oschin telescope. Quaoar was first identified in images by Trujillo on 5 June 2002, when he noticed a dim, 18.6-magnitude object slowly moving among the stars of the constellation Ophiuchus. Quaoar appeared relatively bright for a distant object, suggesting that it could have a size comparable to the diameter of Pluto. To ascertain Quaoar's orbit, Brown and Trujillo initiated a search for archival precovery images, obtaining several from the Near-Earth Asteroid Tracking survey from various observatories in 1996 and 2000–2002, as well as two archival photographic plates taken by astronomer Charles T. Kowal in May 1983. The earliest known precovery image was found by Edward Rhoads on a photographic plate imaged on 25 May 1954 from the Palomar Observatory Sky Survey. The discovery was formally announced by the Minor Planet Center on 7 October 2002, and Quaoar was given the minor planet number 50000 on 20 November 2002, a deliberate choice highlighting its unusual size and the fact that it was discovered during the search for Pluto-sized objects in the Kuiper belt.

Quaoar has a reddish surface made of crystalline water ice, tholins, and traces of frozen methane. It has one moon named Weywot and a potential second moon that has not yet been confirmed. It is believed that Quaoar's elongated shape, gravitational influence of its moon(s), and extremely cold temperature help keep its rings stable. Quaoar orbits the Sun at an average distance of 43.7 AU, taking 288.8 years to complete one full orbit. With an orbital eccentricity of 0.04, Quaoar follows a nearly circular orbit, only slightly varying in distance from 42 AU at perihelion to 45 AU at aphelion. Quaoar has last passed aphelion in late 1932 and is currently approaching the Sun at a rate of 0.035 AU per year; it will reach perihelion around February 2075.

Reader's Guide

Quaoar's discovery has been cited by Brown as having contributed to the reclassification of Pluto as a dwarf planet. Since then, Brown has contributed to the discovery of larger trans-Neptunian objects, including Haumea, Eris, Makemake and Gonggong. The object was given the minor planet number 50000, a deliberate choice highlighting its unusual size and the fact that it was discovered during the search for Pluto-sized objects in the Kuiper belt. Quaoar's two thin rings orbiting outside its Roche limit defy theoretical expectations that rings outside the Roche limit should be unstable. The name Quaoar comes from the creator god of the Tongva people indigenous to the Los Angeles Basin, where Brown's institute, the California Institute of Technology, was located. Brown and Trujillo consulted tribal historian Marc Acuña, who confirmed that the name Kwawar would be appropriate. The Tongva preferred the spelling Qua-o-ar, which Brown and Trujillo adopted, though with the hyphens omitted. Quaoar's name was announced before the official numbering of the object, which Brian Marsden—the head of the Minor Planet Center—remarked in 2004 to be a violation of the protocol, but the name was approved by the Committee on Small Body Nomenclature.

Did You Know?

• Quaoar has two thin rings orbiting outside its Roche limit, which defies theoretical expectations.
• Quaoar's average diameter is 1,100 km (680 mi), about half the size of Pluto.
• The earliest known precovery image of Quaoar was from a photographic plate imaged on 25 May 1954.