Quaoar: Difference between revisions
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'''50000 Quaoar''' ({{pron-en|ˈkwɑːwɑr}} {{respell|KWAH|wahr}})<ref>[http://web.archive.org/web/20060907110231/www.gps.caltech.edu/~chad/quaoar/ Brown's site] gives a three-syllable pronunciation as an approximation of the Tongva {{ |
'''50000 Quaoar''' ({{pron-en|ˈkwɑːwɑr}} {{respell|KWAH|wahr}})<ref>[http://web.archive.org/web/20060907110231/www.gps.caltech.edu/~chad/quaoar/ Brown's site] gives a three-syllable pronunciation as an approximation of the Tongva {{IPA2|qʷɑoɑr|}}. However, his students pronounce it {{IPA-en|ˈkwɑːwɑr|}} with two syllables. (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 [http://365daysofastronomy.org/2009/03/31/march-31st/ podcast: Dwarf Planet Haumea (Darin Ragozzine)] at 3′18″)</ref> 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 E. Brown|Michael Brown]] at the [[California Institute of Technology]] from images acquired at the [[Samuel Oschin Telescope]] at [[Palomar Observatory]]. |
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== Discovery == |
== Discovery == |
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#Quaoar |
#Quaoar |
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circle 1784 1305 97 |
circle 1784 1305 97 Quaoar |
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#Varuna |
#Varuna |
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circle 2420 1305 58 [[20000 Varuna|Varuna]] |
circle 2420 1305 58 [[20000 Varuna|Varuna]] |
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Revision as of 08:40, 17 May 2009
 Sum of 16 Hubble exposures registered on Quaoar. | |
| Discovery[1] | |
|---|---|
| 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 |
| Designations | |
| 2002 LM60 | |
| Cubewano[2][3] | |
| Orbital characteristics[4] | |
| Epoch May 18, 2008 (JD 2 454 600.5) | |
| Aphelion | 6.716 275 Tm (45.286 AU) |
| Perihelion | 6.270 316 Tm (41.928 AU) |
| 6.493 296 Tm (43.607 AU) | |
| Eccentricity | 0.038 4 |
| 105 181.6 d (287.97 a) | |
Average orbital speed | 4.52 km/s |
| 284.861° | |
| Inclination | 7.988° |
| 188.893° | |
| 148.508° | |
| Physical characteristics | |
| Dimensions | 1260 ± 190 km (direct)[5]
844+207 −190 km (thermal)[6] |
| Mass | (1.0–2.6)×1021 kg |
Mean density | 2.0? g/cm³ |
Equatorial surface gravity | 0.276–0.376 m/s² |
Equatorial escape velocity | 0.523–0.712 km/s |
| 0.088 +0.021 −0.012 [5] 0.198 6 +0.13 −0.07 [6] | |
| Temperature | ~43 K |
| (moderately red) B-V=0.94, V-R=0.65 | |
| 19.3[7] | |
| 2.6 | |
50000 Quaoar (Template:Pron-en KWAH-wahr)[8] 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 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.
Size
Error: Image is invalid or non-existent.
Quaoar is estimated to have a diameter of 1260 ± 190 km[5], 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. 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 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 Brown’s pages for a non-technical description and his paper[5] 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.
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)[6].
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, Haumea, and 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[3] and the Deep Ecliptic Survey.[2][9]
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,[2] 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[10] 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 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 ice and have a higher albedo, and thus they present a neutral colour (see colour comparison).
Cryovolcanism
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[11].
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[12].
Since then (2006), crystalline water ice was also found on Haumea, but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7)[13].
More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small (5%) quantity of (solid) methane and ethane[14]. 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[14].
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.[15] 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.[16] 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.[17]
References
- ^ Frequently Asked Questions About Quaoar
- ^ a b c Buie, Marc W. (2006-05-17). "Orbit Fit and Astrometric record for 50000". SwRI (Space Science Department). Retrieved 2008-09-19.
- ^ a b 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.
- ^ Asteroid Data Services by Lowell Observatory
- ^ a b c d 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. doi:10.1086/382513. Reprint on Brown's site (pdf)
- ^ a b c 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
- ^ "AstDys (50000) Quaoar Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2009-03-16.
- ^ Brown's site gives a three-syllable pronunciation as an approximation of the Tongva [qʷɑoɑr]. However, his students pronounce it /ˈkwɑːwɑr/ with two syllables. (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″)
- ^ 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. (2004). "Crystalline water ice on the Kuiper belt object (50000) Quaoar". Nature. 432 (7018): 731–3. doi:10.1038/nature03111.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) PMID 15592406. Reprint on Jewitt's site (pdf) - ^ Crystalline Ice on Kuiper Belt Object (50000) Quaoar - article about crystalline ice on Quaoar
- ^ Trujillo, C. A. |coauthors=Brown M.E., Barkume K., Shaller E., Rabinowitz D. The Surface of 2003 EL61 in the Near Infrared. The Astrophysical Journal, 655 (Feb. 2007), pp. 1172-1178 Preprint
- ^ a b Schaller, E.L.; M.E. Brown Detection of Methane on Kuiper Belt Object (50000) Quaoar. To appear in ApJ Letters (2007) Preprint on arXiv.
- ^ Johnston's Archive[1]
- ^ Distant EKO The Kuiper Belt Electronic newsletter, March 2007
- ^ "Heavenly Bodies and the People of the Earth", Nick Street, Search Magazine, July/August 2008
External links
- Quaoar discoverers' webpage
- Orbital simulation from JPL (Java) / Ephemeris
- 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
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