Discover

'50000 Quaoar' (pronounced ''kwaa'·waar'' or ''kwow'·ər'', English , Tongva ) [1] is a Trans-Neptunian object orbiting the Sun in the Kuiper belt. It 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.

Contents

Discovery

Name

Size

Orbit

Physical characteristics

Satellite

References

External links

Discovery

The discovery of Quaoar, a 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. It may qualify as a dwarf planet, given its size inferred from direct observation by the Hubble Space Telescope.

Name

The planetoid's name follows International Astronomical Union rules by naming 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 made. The IAU approved the name Quaoar, making it the official name; it also has the provisional designation ''.
The "memorable" number 50000 is a witness to the exciting race to discover a Pluto-sized object; Quaoar’s discovery followed that of and was in turn followed by bigger discoveries (see below).The efforts were finally rewarded with the discovery of an object bigger than Pluto, namely .

Size

Image:EightTNOs.png|thumb|250px|left|Quaoar compared to Eris, Pluto, (136472) 2005 FY₉, (136108) 2003 EL₆₁, Sedna, Orcus, Varuna, and Earth.
#Earth
rect 646 1714 2142 1994 The Earth
#Eris and Dysnomia
circle 226 412 16 Dysnomia
circle 350 626 197 (136199) Eris
#Pluto and Charon
circle 1252 684 86 Charon
circle 1038 632 188 (134340) Pluto
#2005 FY9
circle 1786 614 142 (136472) 2005 FY9
#2003 EL61
circle 2438 616 155 (136108) 2003 EL61
#Sedna
circle 342 1305 137 (90377) Sedna
#Orcus
circle 1088 1305 114 (90482) Orcus
#Quaoar
circle 1784 1305 97 (50000) Quaoar
#Varuna
circle 2420 1305 58 (20000) Varuna
desc none
# - setting this to "bottom-right" will display a (rather large) icon linking to the graphic, if desired
#Notes:
#Details on the new coding for clickable images is here:
#While it may look strange, it's important to keep the codes for a particular system in order. The clickable coding treats the first object created in an area as the one on top.
#Moons should be placed on "top" so that their smaller circles won't disappear "under" their respective primaries.

Quaoar is estimated to have a diameter of 1260 ± 190 km,
which at the time of discovery in 2002 made it the largest object found in the solar system since the discovery of Pluto. Quaoar was later supplanted by , , , and . In addition, it is likely that the subsequently discovered plutino 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 (HST) images, using a new, sophisticated method (see Brown’s pages for a non-technical description and his paper 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 (point spread function (PSF)), Brown and Trujillo 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 .
However, these estimates only marginally agree with the recent (2007) infrared measurements by Spitzer Space Telescope suggesting a much larger albedo (0.19) and consequently a smaller diameter ('844.4' km).

Orbit

Orbits of Quaoar (blue) and Pluto (red) - polar view.

Quaoar orbits at about 6 billion kilometres (3.7 billion miles) from the Sun with an orbital period of 287 years.
The orbit is near-circular and moderately-inclined (~8°), typical for the population of ''small'' classical Kuiper Belt objects (KBO) but exceptional among the ''large'' KBO. Varuna, and are all on highly inclined, more eccentric orbits.
The polar view compares the near-circular Quaoar's orbit to highly eccentric (e=0.25) orbit of (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.

Orbits of Quaoar and Pluto - ecliptic view.

At 43 AU
and a near-circular orbit, Quaoar is not significantly perturbed by Neptune, unlike Pluto which is in 2:3 orbital resonance with Neptune. The ecliptic view illustrates the relative inclinations of the orbits of Quaoar and Pluto. 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

Quaoar is believed to be a mixture of rock and ice, like other Kuiper Belt Objects (KBOs); however its very low albedo (estimated at 0.1, but still much higher than that of (0.04)) indicates that the ice has disappeared from Quaoar's 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 °C (110 K or −260 °F) sometime in the last ten million years^[6].
Speculation began as to what could have caused Quaoar to heat up from its natural temperature of −220 °C (55 K or −360 °F). 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 coreNew 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.

Satellite

The discovery of a satellite of Quaoar was reported in IAUC 8812 on 22 February 2007 [2]. The orbit of this satellite has yet to be determined.
The satellite was found at 0.35 arcsec from Quaoar with magnitude difference of 5.6^[8].
Assuming an albedo similar to that of the primary the magnitude suggests the diameter of 100 km.

References

1. http://cfa-www.harvard.edu/iau/lists/NumberedMPs.html
2. http://cfa-www.harvard.edu/iau/MPDes.html
3. http://asteroid.lowell.edu
4. ''Direct Measurement of the Size of the Large Kuiper Belt Object (50000) Quaoar'', Michael E. Brown and Chadwick A. Trujillo, , , The Astronomical Journal, 2004 Reprint on Brown's site (pdf)
5. Stansberry J., Grundy W., Brown M, Cruikshank D., Spencer J., Trilling D., Margot J-L
''Physical Properties of Kuiper Belt and Centaur Objects:
Constraints from Spitzer Space Telescope''
To Appear in: Kuiper Belt (M.A. Barucci et al., Eds.) U. Arizona Press, 2007 Preprint
6. ''Crystalline water ice on the Kuiper belt object (50000) Quaoar'', Jewitt DC. and Luu J., , , Nature, 2004 PMID 15592406. Reprint on Jewitt's site (pdf)
7. C. A. Trujillo, Brown M.E., Barkume K., Shaller E., Rabinowitz D.
''The Surface of in the Near Infrared''. The Astrophysical Journal, '655' (Feb. 2007), pp. 1172-1178 Preprint
8. Distant EKO The Kuiper Belt Electronic newsletter, March 2007

External links

★ Quaoar discoverers' webpage

★ Orbit simulation from NASA JPL site

★ ★ class=wikiexternal target=_blank> Astronomers Contemplate Icy Volcanoes in Far Places - New York Times article

★ Quaoar, the newest planet . . . or is it? - article in an Australian science magazine

★ New Planet-Shaped Body Found in Our Solar System - article in National Geographic

★ Volcanism possible on planet-like Quaoar - CNN.com

★ Chilly Quaoar had a warmer past - Nature.com article