50000 Quaoar

Infobox Planet
minorplanet = yes
discovery=yes
discovery_ref = [ [http://www.chadtrujillo.com/quaoar/ Frequently Asked Questions About Quaoar] ]
physical_characteristics = yes
bgcolour=#FFFFC0
name=50000 Quaoar


caption= Sum of 16 Hubble exposures registered on Quaoar.
discoverer=Chad Trujillo
discovered=2002 Jun 05 10:48:08 PDT on an image taken 2002 June 04 05:41:40 UT
alt_names=2002 LM₆₀
mp_category=Cubewanocite web
author=Marc W. Buie
date=2006/05/17
title=Orbit Fit and Astrometric record for 50000
publisher=SwRI (Space Science Department)
url=http://www.boulder.swri.edu/~buie/kbo/astrom/50000.html
accessdate=2008-09-19] cite web|date=2008-07-17 |title=MPEC 2008-O05 : Distant Minor Planets (2008 Aug. 2.0 TT) |author=Brian G. Marsden |work=IAU Minor Planet Center |publisher=Harvard-Smithsonian Center for Astrophysics |url=http://cfa-www.harvard.edu/iau/mpec/K08/K08O05.html |accessdate=2008-10-01]
orbit_ref = [ [http://asteroid.lowell.edu Asteroid Data Services by Lowell Observatory ] ]
epoch=May 18, 2008 (JD 2 454 600.5)
semimajor=6.493 296 Tm (43.607 AU)
perihelion=6.270 316 Tm (41.928 AU)
aphelion=6.716 275 Tm (45.286 AU)
eccentricity=0.038 4
period=105 181.6 d (287.97 a)
inclination=7.988°
asc_node=188.893°
arg_peri=148.508°
mean_anomaly=284.861°
avg_speed=4.52 km/s
dimensions= 1260 ± 190 km (direct)cite journal | author=Michael E. Brown and Chadwick A. Trujillo | title="Direct Measurement of the Size of the Large Kuiper Belt Object (50000) Quaoar"| journal=The Astronomical Journal | volume=127 | issue=7018 | year=2004 | pages=2413–2417 | doi=10.1086/382513 [http://www.gps.caltech.edu/~mbrown/papers/ps/qu.pdf Reprint ] on Brown's site (pdf)] 844±|207|190 km (thermal)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 [http://www.arxiv.org/abs/astro-ph/0702538 Preprint] ]
mass=(1.0–2.6)e|21 kg
density=2.0? g/cm³
surface_grav=0.276–0.376 m/s²
escape_velocity=0.523–0.712 km/s
spectral_type=(moderately red) B-V=0.94, V-R=0.65
abs_magnitude=2.6
albedo=0.088 ±|0.021|0.012 0.198 6 ±|0.13|0.07
single_temperature=~43 K

50000 Quaoar (pron-en|ˈkwɑː.oʊ.ɑr respell|KWAH|oh-ahr or IPAlink-en|ˈkwɑːwɑr respell|KWAH|wahr, Tongva IPAlink|qʷɑoɑr, [http://web.archive.org/web/20060907110231/www.gps.caltech.edu/~chad/quaoar/] ) is a Trans-Neptunian object and likely 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

The planetoid's name follows International Astronomical Union rules by naming trans-Neptunian objects after deities associated with creation myths (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 mp|2002 LM|60. The “memorable” number 50000 is a witness to the exciting race to discover a Pluto-sized object; Quaoar’s discovery followed that of dp|Varuna|20000 Varuna 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 dp|Eris.

Size

---

thumb|250px|left|Quaoar_compared_to_Eris,_Pluto,_Makemake,_Haumea,_Sedna,_Orcus,_Varuna,_and_Earth.
#Earthrect 646 1714 2142 1994 The Earth
#Eris and Dysnomiacircle 226 412 16 Dysnomiacircle 350 626 197 (136199) Eris
#Pluto and Charoncircle 1252 684 86 Charoncircle 1038 632 188 (134340) Pluto
#Makemakecircle 1786 614 142 (136472) Makemake
#Haumeacircle 2438 616 155 (136108) Haumea
#Sednacircle 342 1305 137 (90377) Sedna
#Orcuscircle 1088 1305 114 (90482) Orcus
#Quaoarcircle 1784 1305 97 (50000) Quaoar
#Varunacircle 2420 1305 58 (20000) Varuna
#link to image (under all other links)rect 0 0 2749 1994

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 dp|Eris, dp|Sedna, dp|Haumea, and dp|Makemake. In addition, it is likely that the subsequently discovered plutino dp|Orcus 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 [http://www.gps.caltech.edu/~mbrown 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 size which would give a similar blurred image. This method was recently applied by the same authors to measure the size of dp|Eris.

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 ±|206.7|189.6 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, dp|Haumea, and dp|Makemake 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. [A lot of TNOs classified as cubewanos by the MPC are classified as ScatNear (Scattered by Neptune) by the DES.]

The polar view compares the near-circular Quaoar's orbit to highly eccentric (e=0.25) orbit of dp|Pluto (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 13.9 AUcite web |url=http://home.comcast.net/~kpheider/50000.txt |title=50000 Quaoar distance (AU) from Pluto |accessdate=2007-12-18] from Pluto making it the closest large body to the Pluto-Charon system. By Kuiper Belt standards this is very close.

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 dp|Varuna (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 cite journal | author=Jewitt DC. and Luu J. | title="Crystalline water ice on the Kuiper belt object (50000) Quaoar" | journal=Nature | volume=432 | issue=7018 | year=2004 | pages=731–3 | doi=10.1038/nature03111 PMID 15592406. [http://www.ifa.hawaii.edu/~jewitt/papers/2004/JL2004.pdf Reprint] on Jewitt's site (pdf)] .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 coreC. A. Trujillo, Brown M.E., Barkume K., Shaller E., Rabinowitz D."The Surface of mp|2003 EL|61 in the Near Infrared". The Astrophysical Journal, 655 (Feb. 2007), pp. 1172-1178 [http://arxiv.org/abs/astro-ph/0601618 Preprint] ] .

More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small (5%) quantity of (solid) methane and ethaneE.L. Schaller, M.E. Brown"Detection of Methane on Kuiper Belt Object (50000) Quaoar". To appear in ApJ Letters (2007) [http://arxiv.org/abs/0710.3591 Preprint on arXiv.] ] .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, dp|Eris, dp|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.

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. [Johnston's Archive [http://www.johnstonsarchive.net/astro/astmoons/am-50000.html] ] 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. [http://www.boulder.swri.edu/ekonews/issues/past/n051/html/index.html Distant EKO] The Kuiper Belt Electronic newsletter, March 2007] 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. [ [http://www.searchmagazine.org/Archives/Back%20Issues/July-August%202008/full-heavenly-bodies.html "Heavenly Bodies and the People of the Earth"] , Nick Street, "Search Magazine," July/August 2008]

References