50000 Quaoar

**50000 Quaoar** (symbol: ) is a Trans-Neptunian object and is also a dwarf planet.  It was discovered on June 4, 2002 by  Chad Trujillo and Michael Brown at the California Institute of Technology.

Quaoar has one known moon, named Weywot. It also has a ring. Unexpectedly, the ring is at twice the distance of the Roche limit, which was thought to be the maximum distance of a ring: beyond the Roche limit, the particles in a ring should clump together and form a moon; yet this has not happened to Quaoar's ring. It is thought that the particles do not clump together because of tides created by Weywot. There may also be small shepherd moons on either side of the ring, as there are at Saturn's F Ring.

## Physical characteristics 
### Size and shape 
, measurements of Quaoar's shape from its rotational light curve and stellar occultations show that Quaoar is a triaxial ellipsoid with an average diameter of . At the time of its discovery in 2002, Quaoar was the largest object found in the Solar System since the discovery of Pluto. Slowly-rotating objects in hydrostatic equilibrium are expected to be oblate spheroids (Maclaurin spheroids), whereas rapidly-rotating objects in hydrostatic equilibrium, such as Haumea which rotates in nearly 4 hours, are expected to be flattened and elongated ellipsoids (Jacobi ellipsoids).

### Mass and density 
 and the Moon]]
Quaoar has a mass of , which was determined from Weywot's orbit using Kepler's third law. Many Kuiper belt objects such as 20000 Varuna and 28978 Ixion share a similar moderately red color.

Spectroscopic observations by David Jewitt and Jane Luu in 2004 revealed signs of crystalline water ice and ammonia hydrate on Quaoar's surface. These substances are expected to gradually break down due to solar and cosmic radiation, and crystalline water ice can only form in warm temperatures of at least , so the presence of crystalline water ice on Quaoar's surface indicates that it was heated to this temperature sometime in the last ten million years.

More precise observations of Quaoar's near infrared spectrum in 2007 indicated the presence of small quantities (5%) of solid methane and ethane. Given its boiling point of , methane is a volatile ice at average surface temperatures of Quaoar, unlike water ice or ethane. Both models and observations suggest that only a few larger bodies (Pluto,  and ) can retain the volatile ices whereas the dominant population of small trans-Neptunian objects lost them. Quaoar, with only small amounts of methane, appears to be in an intermediary category.

In 2022, low-resolution near-infrared (0.7–5 μm) spectroscopic observations by the James Webb Space Telescope (JWST) revealed the presence of carbon dioxide ice, complex organics, and significant amounts of ethane ice on Quaoar's surface. Other possible chemical compounds include hydrogen cyanide and carbon monoxide. JWST also took medium-resolution near-infrared spectra of Quaoar and found evidence of small amounts of methane on Quaoar's surface. However, both JWST's low- and medium-resolution spectra of Quaoar did not show conclusive signs of ammonia hydrates. With a measured mean temperature of approximately , the upper limit of Quaoar's atmospheric pressure is expected to be in the range of a few microbars.

## Notes 
## References 
## Other websites 
* Quaoar discoverers' webpage
* Orbital simulation from JPL (Java) /Ephemeris