Sum of 16 Hubble exposures registered on Quaoar
|Discovery and designation|
|Discovered by||Chad Trujillo, Michael Brown|
|Discovery date||2002 Jun 05 10:48:08 PDT on an image taken 2002 June 04 05:41:40 UT|
|Pronunciation||/ˈkwɑːwɑr/ KWAH-war [a]|
|Alternative names||2002 LM60|
|Minor planet category||Cubewano|
|Epoch July 23, 2010 (JD 2 455 400.5)|
|Aphelion||45.116 AU (6.749 189 Tm)|
|Perihelion||41.695 AU (6.237 516 Tm)|
|Semi-major axis||43.405 AU (6.493 353 Tm)|
|Orbital period||285.97 a (104 451.3 d)|
|Average orbital speed||4.52 km/s|
|Longitude of ascending node||189.033°|
|Argument of perihelion||155.624°|
(81±11 km diameter)
1170 km (occultation, longest chord)
−190 km (thermal)
1.4 ± 0.1 ×1021 kg
|Mean density||low end of 4.2±1.3 g/cm3
2.8 g/cm3 (assuming moon highly eccentric)
|Equatorial surface gravity||0.276–0.376 m/s2|
|Equatorial escape velocity||0.523–0.712 km/s|
|Sidereal rotation period||17.6788 hours|
|Geometric albedo||0.199 +0.13
|Spectral type||(moderately red) B-V=0.94, V-R=0.64|
|Absolute magnitude (H)||2.48±0.76|
50000 Quaoar ("Kwawar") is a rocky trans-Neptunian object in the Kuiper belt with one known moon. Several astronomers believe it to be a dwarf planet, and is massive enough to be considered one under the 2006 draft proposal of the IAU, though the IAU has not formally recognized it as such.
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. The discovery of this 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.
Quaoar is named for the Tongva creator god, following International Astronomical Union naming conventions for non-resonant Kuiper belt objects. The Tongva are the native people of the area around Los Angeles, where the discovery of Quaoar was made. Brown et al. had picked the name with the more intuitive spelling Kwawar, but the preferred spelling among the Tongva was Qua-o-ar.
Prior to IAU approval of the name, Quaoar went by the provisional designation 2002 LM60. 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.
|This article is outdated. (September 2011)|
In 2004, Quaoar was estimated to have a diameter of 1260 ± 190 km, subsequently revised downward, 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 Eris, Sedna, Haumea, and Makemake. Quaoar is about as massive as (if somewhat smaller than) Pluto's moon Charon, which is approximately 2½ times as massive as Orcus. Quaoar is roughly one fifteenth the diameter of Earth, one quarter the diameter of the Moon, and a third 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 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 Eris.
The uncorrected 2004 HST estimates only marginally agree with the 2007 infrared measurements by the Spitzer Space Telescope which suggest a brighter albedo (0.19) and consequently a smaller diameter (844.4 +206.7
−189.6 km). During the 2004 HST observations, little was known about the surface properties of Kuiper belt objects, but we now know that the surface of Quaoar is in many ways similar to those of the icy satellites of Uranus and Neptune. Adopting a Uranian-satellite limb darkening profile suggests that the 2004 HST size estimate for Quaoar was approximately 40% too large, and that a more proper estimate would be about 900 km. Using a weighted average of the Spitzer and corrected HST estimates, Quaoar, as of 2010, can be estimated at about 890 ± 70 km in diameter.
On 2011-05-04 Quaoar occulted a 16th-magnitude star, which gave 1170 km as the longest chord and suggests an elongated shape. New measurement from Herschel Space Observatory with revised data from SST suggested that Quaoar has diameter 1070 ± 38 km and Weywot 81 ± 11 km.
Dwarf planet? 
Since Quaoar is a binary object, the mass of the system can be calculated from the orbit of the secondary. Quaoar's estimated density of around 2.2 g/cm3 and estimated size of 1,100 km suggests that it should qualify as a dwarf planet if the mass required for hydrostatic equilibrium is proven. Mike Brown estimates that rocky bodies around 900 km in diameter relax into hydrostatic equilibrium, and that icy bodies relax into hydrostatic equilibrium somewhere between 200 and 400 km. With an estimated mass greater than 1.6×1021 kg, Quaoar has the mass and diameter "usually" required for being in hydrostatic equilibrium according to the 2006 IAU draft definition of a planet (5×1020 kg, 800 km), and Brown states that Quaoar "must be" a dwarf planet. Light-curve-amplitude analysis shows only small deviations, suggesting that Quaoar is indeed a spheroid with small albedo spots and hence a dwarf planet.
Hit-and-run collision 
Planetary scientist Erik Asphaug has suggested that Quaoar may have collided with a much larger body, stripping the lower-density mantle from Quaoar, and leaving behind the denser core. He envisions that Quaoar was originally covered by a mantle of ice that made it 300 to 500 kilometers bigger than it is today, and that it collided with another Kuiper-belt body about twice its size—an object roughly the diameter of Pluto (or even approaching the size of Mars), possibly Pluto itself.
The orbit is near-circular and moderately-inclined at approximately 8°, typical for the population of small classical Kuiper-belt objects (KBO) but exceptional among the large KBO. Varuna, Haumea, and Makemake 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 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 14 AU from Pluto making it the closest large body to the Pluto–Charon system. By Kuiper Belt standards this is very close.
Physical characteristics 
With a density estimated to be around 4.2±1.3 g/cm3, Quaoar is believed to be a mixture of mostly rock with some ice and is possibly the densest known object in the Kuiper belt. Even dwarf planet Haumea is only estimated to have a density of 2.6 g/cm3. The albedo could be as low as 0.1, which would still be much higher than the lower estimate of 0.04 for Varuna. This may indicate that fresh ice has disappeared from Quaoar's surface. 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 fresh ice and have a higher albedo, and thus they present a neutral colour (see colour comparison).
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.
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, Eris, 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.
Quaoar has one known satellite, Weywot, formally (50000) Quaoar I Weywot. Its discovery was reported in IAUC 8812 on 22 February 2007. The satellite was found at 0.35 arcsec from Quaoar with an apparent magnitude difference of 5.6. It orbits at a distance of 14,500 km from the primary and has an orbital eccentricity of about 0.14. Assuming an equal albedo and density to the primary, the apparent magnitude suggests that the moon has a diameter of about 74 km (1:12 of Quaoar). Brown believes it is likely to be a collisional fragment of Quaoar, which he speculates lost much of its ice mantle in the process. Weywot is estimated to only have 1:2000 the mass of Quaoar.
- Frequently Asked Questions About Quaoar
- Buie, Marc W. (2006-05-17). "Orbit Fit and Astrometric record for 50000". SwRI (Space Science Department). Retrieved 2008-09-19.
- Marsden, Brian G. (2008-07-17). "MPEC 2008-O05 : Distant Minor Planets (2008 Aug. 2.0 TT)". IAU Minor Planet Center. Harvard-Smithsonian Center for Astrophysics. Retrieved 2008-10-01.
- Daniel W. E. Green (2007-02-22). "IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637), (90482)". International Astronomical Union Circular. Retrieved 2009-03-26.
- JPL, NASA (2010-06-16 last obs). "JPL Small-Body Database Browser". National Aeronautics and Space Administration. Jet Propulsion Laboratory. Retrieved 2010-01-02.
- Asteroid Data Services by Lowell Observatory
- S. Fornasier, E. Lellouch, T. Müller, P. Santos-Sanz, P. Panuzzo, C. Kiss, T. Lim, M. Mommert, D. Bockelée-Morvan, E. Vilenius, J. Stansberry, G.P. Tozzi, S. Mottola, A. Delsanti, J. Crovisier, R. Duffard, F. Henry, P. Lacerda, A. Barucci, A. Gicquel (2013). "TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of 9 bright targets at 70–500 μm". arXiv:1305.0449v2.
- Braga-Ribas et al. 2011, "Stellar Occultations by TNOs: the January 08, 2011 by (208996) 2003 AZ84 and the May 04, 2011 by (50000) Quaoar", EPSC Abstracts, vol. 6
- John Stansberry; Will Grundy; Mike Brown; Dale Cruikshank; John Spencer; David Trilling; Jean-Luc Margot (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". arXiv:astro-ph/0702538 [astro-ph].
- Fraser et al. (2013)
- Brown, Michael E.; Fraser, Wesley C. (2010). "Quaoar: A Rock in the Kuiper belt". The Astrophysical Journal 714 (2): 1547. arXiv:1003.5911. Bibcode:2010ApJ...714.1547F. doi:10.1088/0004-637X/714/2/1547.
- Brown, M.E.; Fraser, Wesley (2009). "Quaoar: A Rock in the Kuiper Belt". DPS meeting #41. American Astronomical Society. Bibcode:2009DPS....41.6503F. (Backup reference)
- Tegler, Stephen C. (2007-02-01). "Kuiper Belt Object Magnitudes and Surface Colors". Archived from the original on 21 May 2006. Retrieved 2006-04-23.
- "AstDys (50000) Quaoar Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2009-03-16.
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- "Planetary Names: Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. International Astronomical Union (Working Group for Planetary System Nomenclature). Retrieved 10 June 2012.
- NASA. "List of Dwarf Planets". Retrieved 2012-06-09.
- Brown, Michael E. 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. Bibcode:2004AJ....127.2413B. doi:10.1086/382513. Reprint on Brown's site (pdf)
- Mike Brown. "The Dwarf Planets". Archived from the original on 29 January 2008. Retrieved 2008-01-20.
- "The IAU draft definition of "planet" and "plutons"". IAU. August 2006. Archived from the original on 9 January 2010. Retrieved 2009-12-16. (XXVI)
- Tancredi, G., & Favre, S. (2008) Which are the dwarfs in the Solar System?. Depto. Astronomía, Fac. Ciencias, Montevideo, Uruguay; Observatorio Astronómico Los Molinos, MEC, Uruguay. Retrieved 10-08-2011
- George Musser (2009-10-13). "What do we really know about the Kuiper Belt? Fifth dispatch from the annual planets meeting". Scientific American blog. Archived from the original on 14 October 2009. Retrieved 2009-10-13.
- Ron Cowen (2009-01-04). "On the Fringe". ScienceNews. Archived from the original on 7 January 2010. Retrieved 2010-01-04.
- A lot of TNOs classified as cubewanos by the MPC are classified as ScatNear (Scattered by Neptune) by the DES.
- "50000 Quaoar distance (AU) from Pluto". Retrieved 2008-11-21.
- Jewitt, D.C.; J. Luu (2004). "Crystalline water ice on the Kuiper belt object (50000) Quaoar". Nature 432 (7018): 731–3. Bibcode:2004Natur.432..731J. doi:10.1038/nature03111. PMID 15592406.. Reprint on Jewitt's site (pdf)
- Crystalline Ice on Kuiper Belt Object (50000) Quaoar – article about crystalline ice on Quaoar
- Trujillo; Brown; Barkume; Schaller; Rabinowitz (2007). "The Surface of 2003EL61 in the Near Infrared". The Astrophysical Journal 655 (2): 1172. arXiv:astro-ph/0601618. Bibcode:2007ApJ...655.1172T. doi:10.1086/509861.
- Schaller, E.L.; M.E. Brown (2007). "Detection of Methane on Kuiper Belt Object (50000) Quaoar". The Astrophysical Journal Letters 670 (1): L49–L51. arXiv:0710.3591. Bibcode:2007ApJ...670L..49S. doi:10.1086/524140.
- Wm. Robert Johnston (2008-11-25). "(50000) Quaoar". Johnston's Archive. Archived from the original on 11 April 2009. Retrieved 2009-05-26.
- Distant EKO The Kuiper Belt Electronic newsletter, March 2007
- "Heavenly Bodies and the People of the Earth", Nick Street, Search Magazine, July/August 2008
- MPC 67220
- Frequently Asked Questions About Quaoar
- E. L. Schaller, M. E. Brown, "Detection of Additional Members of the Haumea Collisional Family via Infrared Spectroscopy". AAS DPS conference, 13 Oct. 2008; also podcast: Dwarf Planet Haumea (Darin Ragozzine) at 3′18″
|Wikimedia Commons has media related to: Quaoar|
- Quaoar discoverers' webpage
- Orbital simulation from JPL (Java) / Ephemeris
- Quaoar could have hit a bigger Pluto-sized body at high speeds (Video Credit: Craig Agnor, E. Asphaug)
- Data at Johnston's Archive
- Astronomers Contemplate Icy Volcanoes in Far Places – New York Times article
- Quaoar, the newest planet . . . or is it? – article in an Australian newspaper
- 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
- Cryovolcanism on Charon and other Kuiper Belt Objects
- The Mass, Orbit, and Tidal Evolution of the Quaoar-Weywot System (arXiv:1211.1016 : 5 Nov 2012)