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Quaoar is a Trans-Neptunian object orbiting the Sun .

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50000 Quaoar.
Sum of 16 Hubble exposures registered on Quaoar.
Discovery A
Discoverer Chad Trujillo,
Michael E. Brown
Discovery date June 4, 2002
designations B
2002 LM60
Category Kuiper belt
Orbital elements C
Epoch October 22, 2004 (JD 2453300.5)
eccentricity (e) 0.034
Semi-major axis (a) 6.493296 Tm (43.405 AU)
perihelion (q) 6.270316 Tm (41.914 AU)
aphelion (Q) 6.716275 Tm (44.896 AU)
Orbital period (P) 104449.918 d (285.97 a)
Mean orbital speed 4.52 km/s
inclination (i) 7.983º
Longitude of the
ascending node (O)
Argument of
perihelion (?)
Mean anomaly (M) 273.737º
Physical characteristicsD
Dimensions 1260 190 km
mass 1.0-2.61021 kg
density 2.0? g/cm
Surface gravity 0.276-0.376 m/s
escape velocity 0.523-0.712 km/s
Rotation period  ? d
Spectral class (moderately red) B-V=0.94, V-R=0.65
Absolute magnitude 2.6
Albedo (geometric) 0.088+0.021-0.012
Mean surface
~43 K

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. This 18.5 Magnitude object creeping across the summer constellation Ophiuchus was announced on October 7, 2002, at a meeting of the American Astronomical Society. The earliest precovery turned out to be a May 25, 1954 plate from Palomar Observatory. Quaoar may qualify as a Dwarf planet, given Quaoar's size inferred from direct observation by the Hubble Space Telescope.

Name of Quaoar.

The planetoid's name follows International Astronomical Union rules by naming all trans-Neptunian objects 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 provisional designation 2002 LM60. The memorable number 50000 is a witness to the exciting race to discover a Pluto-sized object; Quaoar’s discovery followed that of 20000 Varuna and was in turn followed by bigger discoveries (see above).The efforts were finally rewarded with the discovery of an object bigger than Pluto, namely Eris.

Size of Quaoar.

Quaoar compared to Eris, Pluto, 2005 FY9, 2003 EL61, Sedna, Orcus, Varuna, and Earth.

Quaoar is estimated to have a diameter of 1260 190 km, which at the time of discovery in 2002 made it the largest Minor planet found in the Solar System since the discovery of Pluto. Quaoar was later supplanted by Eris, Sedna, 2003 EL61, and 2005 FY9. In addition, it is likely that the subsequently discovered Plutino Orcus is also larger than Quaoar. Quaoar's volume is somewhat more than all of the asteroids put together, it is about one tenth the diameter of Earth, one third the diameter of the Moon or about half the size of Pluto.

Hubble photo used to measure size of Quaoar.

Quaoar was the first Trans-Neptunian object to be measured directly from Hubble Space Telescope images, using a new sophisticated method (see Brown’s pages for a non-technical description and his paper cited in references for details). Given its distance Quaoar is on the limit of the HST resolution (40 milliarcseconds) and its image is consequently smeared on a few adjacent pixels. By comparing carefully this image with the images of stars in the background and using a sophisticated model of HST optics (PSF), Brown and Troujillo were able to find the best fit disk's size which would give a similar blurred image. This method was recently applied by the same authors to measure the size of Eris.

Orbit of Quaoar.

Quaoar orbits at about 6 billion kilometres (3.7 billion miles) from the Sun with an orbital period of 287 years. It has a more typical planetary orbit than Pluto does-a near-circular, moderately-inclined (~8º) orbit with a radius of ~43 AU as shown on the polar view (Quaoar’s orbit in blue, Pluto’s in red, Neptune in grey). The spheres illustrate the current (April 2006) positions, relative sizes and colours. The perihelia (q), aphelia (Q) and the dates of passage are also marked.

Quaoar is classified as a classical Trans-Neptunian object. Its cold orbit is however unusual for large classical objects that typically follow more eccentric and more inclined orbits (see cubewanos for the comparison and the definition of cold and hot families).

At 43 AU and a near-circular orbit, unlike Pluto which is in 2:3 orbital resonance with Neptune, Quaoar is not significantly perturbed by Neptune.

The ecliptic view illustrates the comparison of Quaoar' near-circular, moderately-inclined orbit with Pluto's highly inclined (~17º), highly eccentric (e=0.25) orbit. Note that Pluto's aphelion is beyond (and below) Quaoar's orbit, so that Pluto is closer to the Sun than Quaoar at some times of its orbit, and farther at others.

Physical characteristics of Quaoar.

Orbits of Quaoar.
Orbits of Quaoar and Pluto - ecliptic view.

Quaoar is believed to be a mixture of rock and ice, like other Kuiper Belt objects; however its very low Albedo (estimated at 0.1 but still much higher than that of Varuna: 0.04) indicates that the ice has disappeared from Quaoars outer layers. The surface is moderately red, meaning that the object is relatively more reflective in the red and near-infrared than in the blue. 20000 Varuna and 28978 Ixion are also moderately red in the spectral class. Larger KBOs are often much brighter because they are covered in more ice and have a higher albedo, and thus they present a neutral colour (see colour comparison).

In 2004, scientists were surprised to find signs of crystalline ice on Quaoar, indicating that the temperature rose to at least -160 ºC (110 K or -260 ºF) 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 ºC (55 K or -360 ºF). 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 (Jewitt & Luu, 2004).

Since then (2006), crystalline water ice was also found on 2003 EL61 but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7).

If the New Horizons mission visits several Kuiper Belt Objects after visiting Pluto in 2015, our knowledge of the surfaces of small KBOs should improve but encounters with large objects seem unlikely.

References to Quaoar.

  • Michael E. Brown and Chadwick A. Trujillo (2004). "Direct Measurement of the Size of the Large Kuiper Belt Object (50000) Quaoar". The Astronomical Journal 127 (7018): 2413-2417. Reprint on Brown's site (pdf).
  • Jewitt DC, Luu J (2004). "Crystalline water ice on the Kuiper belt object (50000) Quaoar". Nature 432 (7018): 731-3. Reprint on Jewitt's site (pdf).

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