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50000 Quaoar
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50000 Quaoar is a Trans-Neptunian object and potential dwarf planet 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.
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.
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50000 Quaoar is a Trans-Neptunian object and potential dwarf planet 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.
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
Quaoar is named for the Tongva creator god, following International Astronomical Union naming conventions for non-resonant Kuiper belt objects. (See planetary nomenclature.) The Tongva are the native people of the area around Los Angeles, where the discovery of Quaoar was made. Prior to IAU approval of the name, Quaoar went by the provisional designation . 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.
Size
Image:EightTNOs.png|thumb|250px|left|Quaoar compared to Eris, Pluto, Makemake, Haumea, 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
- Makemake
circle 1786 614 142 (136472) Makemake
- Haumea
circle 2438 616 155 (136108) Haumea
- 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
- link to image (under all other links)
rect 0 0 2749 1994
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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 roughly one tenth the diameter of Earth, one third the diameter of the Moon or half the size of Pluto.
Quaoar was the first trans-Neptunian object to be measured directly from Hubble Space Telescope (HST) images, using a new, sophisticated method (see 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 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
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.
Quaoar is the largest body that is classified as a cubewano by both the Minor Planet Center and the Deep Ecliptic Survey.
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.
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.
As of 2008, Quaoar is currently only 14 AU
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.
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 core.
Since then (2006), crystalline water ice was also found on , but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7).
More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small (5%) quantity 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, , ) 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.
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.
Satellite
The discovery of a satellite of Quaoar was reported in IAUC 8812 on 22 February 2007. 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.
Assuming an albedo similar to that of the primary the magnitude suggests a diameter of 100 km. Brown believes it is likely to be a collisional fragment of Quaoar, which he speculates lost much of its ice mantle in the process.
Brown has left the choice of a name up to the Tongva, who have reportedly chosen the sky god Weywot, son of Quaoar. However, the Tongva have yet to formally inform Brown or the IAU of their decision.
External links
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- from JPL (Java) /
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- - New York Times article
- - article in an Australian newspaper
- - article in National Geographic
- - CNN.com
- - Nature.com article
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