50000 Quaoar is a rocky trans-Neptunian object in the Kuiper belt with one known moon. Several astronomers consider it to be a dwarf planet, although the IAU has not formally designated it as such yet.
Discovery
Quaoar was discovered on June 4, 2002 by astronomers Chad Trujillo and Michael Brown at the California Institute of Technology, from images acquired at the Samuel Oschin Telescope at Palomar Observatory.
The discovery of this magnitude 18.5 object, located in the constellation Ophiuchus, was announced on October 7, 2002, at a meeting of the American Astronomical Society.
The earliest prediscovery image proved to be a May 25, 1954 plate from Palomar Observatory.
Naming
Prior to IAU approval of the name, Quaoar went by the provisional designation 2002 LM60.
The minor planet number 50000 was not coincidence, but chosen to commemorate a particularly large object found in the search for a Pluto-sized object in the Kuiper belt, parallel to the similarly numbered 20000 Varuna.
However, later even larger discoveries were simply numbered according to the order in which their orbits were confirmed.
Quaoar is named for the Tongva creator god, following International Astronomical Union naming conventions for non-resonant Kuiper belt objects. The Tongva are the native people of the area around Los Angeles, where the discovery of Quaoar was made.
In the mythology of the so-called Mission Indians of coastal Southern California, Chingichngish (also spelled Chinigchinix, Chinigchinich, Changitchnish, etc.) also known as Quaoar (also Qua-o-ar, Kwawar, etc.) and by other names including Ouiamot, Tobet and Saor is the name of an important figure.
Chinigchinix was born, or first appeared, after the death of Wiyot, a tyrannical ruler of the first beings, who was poisoned by his sons. Wiyot's murder brought death into the world, and as a consequence, the male creator Night divided the first human ancestors into distinct peoples, assinging them languages and territories.
Stats
Estimated Diameter: 1170 km
Aphelion: 45.12 AU
Perihelion: 41.70 AU
Semi-major axis: 43.41 AU
Orbital Period: 285.97 years
Rotation period: 17.68 hrs
Date discovered: 2002.6.4
Satellite: 1
Classification: TNO, KBO - Cubewano
Star Occultation
On 2011-05-04 Quaoar occulted a 16th-magnitude star, which gave 1170 km as the longest chord and suggests an elongated shape.
Orbit
Quaoar orbits at about 43 astronomical units from the Sun with an orbital period of 286 years. Quaoar's orbit is near-circular and moderately-inclined at approximately 8°, and is not significantly perturbed by Neptune, unlike Pluto which is in 2:3 orbital resonance with Neptune.
Quaoar is the second largest body that is classified as a cubewano.
Physical characteristics
With a density estimated to be around 4.2 ± 1.3 g/cm3, Quaoar is believed to be a mixture of mostly rock with some ice and is possibly the densest known object in the Kuiper belt. Even dwarf planet Haumea is only estimated to have a density of 2.6 g/cm3.
Planetary scientist Erik Asphaug has suggested that Quaoar may have collided with a small planet up to the size of Mars, stripping the lower-density mantle from Quaoar, and leaving behind the denser core. He envisions that Quaoar was originally covered by a mantle of ice that made it 300 to 500 kilometers bigger than it is today, and that it collided with another Kuiper-belt body about twice its size — an object roughly the diameter of Pluto, possibly Pluto itself.
As of 2008, Quaoar is currently only 14 AU from Pluto making it the closest large body to the Pluto–Charon system. By Kuiper Belt standards this is very close.
Cryovolcanism
In 2004, scientists were surprised to find signs of crystalline ice on Quaoar, indicating that the temperature rose to at least −160 °C sometime in the last ten million years.
Speculation began as to what could have caused Quaoar to heat up from its natural temperature of −220 °C. Some have theorized that a barrage of mini-meteors may have raised the temperature, but the most discussed theory speculates that cryovolcanism may be occurring, spurred by the decay of radioactive elements within Quaoar's core.
More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small quantity (5%) of (solid) methane and ethane. Given its boiling point (112 K), methane is a volatile ice at average Quaoar surface temperatures, unlike water ice or ethane (boiling point 185 K).
Both models and observations suggest that only a few larger bodies (Pluto, Eris, Makemake) can retain the volatile ices while the dominant population of small TNOs lost them. Quaoar, with only small amounts of methane, appears to be in an intermediary category.
Moon
Quaoar has one known satellite, Weywot.
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