50000 Quaoar
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Sum of 16 Hubble exposures registered on Quaoar.
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Discovery[1] and designation
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| Discovered by | Chad Trujillo, Michael E. Brown |
| Discovery date | June 4, 2002 |
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Designations
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| Alternate name[3] | 2002 LM60 [2] |
| Minor planet category |
Kuiper belt |
| Epoch May 18, 2008 (JD 2454600.5) | |
| Aphelion | 6.716275 Tm (45.286 AU) |
| Perihelion | 6.270316 Tm (41.928 AU) |
| Semi-major axis | 6.493296 Tm (43.607 AU) |
| Eccentricity | 0.0384 |
| Orbital period | 105181.6 d (287.97 a) |
| Average orbital speed | 4.52 km/s |
| Mean anomaly | 284.861° |
| Inclination | 7.988° |
| Longitude of ascending node | 188.893° |
| Argument of perihelion | 148.508° |
| Dimensions | 1,260 ± 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 |
| Geometric albedo | 0.088 +0.021−0.012 [5] 0.1986 +0.13−0.07 [6] |
| Temperature | ~43 K |
| Spectral type | (moderately red) B-V=0.94, V-R=0.65 |
| Absolute magnitude (H) | 2.6 |
50000 Quaoar (pronounced /ˈkwɑːwɑr/ or /ˈkwaʊɚ/ (KWAH-wahr or KWOW-ər), Tongva [qʷɑoɑr], [1]) 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.
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[edit] 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.
[edit] 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 2002 LM60. The “memorable” number 50000 is a witness to the exciting race to discover a Pluto-sized object; Quaoar’s discovery followed that of 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 Eris.
[edit] Size
Quaoar is estimated to have a diameter of 1,260 ± 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, 2003 EL61, 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].
[edit] 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, 2003 EL61 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 13.9 AU[7] from Pluto making it the closest large body to the Pluto-Charon system. By Kuiper Belt standards this is very close.
[edit] 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 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[8]. 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[9].
Since then (2006), crystalline water ice was also found on 2003 EL61 but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7)[10].
More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small (5%) quantity of (solid) methane and ethane[11]. 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[11].
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.
[edit] 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[12]. Assuming an albedo similar to that of the primary the magnitude suggests a diameter of 100 km.
[edit] References
- ^ Discovery Circumstances: Numbered Minor Planets
- ^ Minor Planet Designations
- ^ Minor Planet Designations
- ^ Asteroid Data Services by Lowell Observatory
- ^ a b c d Michael E. Brown 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:. 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
- ^ "50000 Quaoar distance (AU) from Pluto". Retrieved on 2007-12-18.
- ^ Jewitt DC. and Luu J. (2004). "Crystalline water ice on the Kuiper belt object (50000) Quaoar". Nature 432 (7018): 731–3. doi:. PMID 15592406. Reprint on Jewitt's site (pdf)
- ^ Crystalline Ice on Kuiper Belt Object (50000) Quaoar - article about crystalline ice on Quaoar
- ^ C. A. Trujillo, 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 E.L. Schaller, M.E. Brown Detection of Methane on Kuiper Belt Object (50000) Quaoar. To appear in ApJ Letters (2007) Preprint on arXiv.
- ^ Distant EKO The Kuiper Belt Electronic newsletter, March 2007
[edit] External links
- Quaoar discoverers' webpage
- Orbital simulation from JPL (Java) / Ephemeris
- 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
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