Information about 50000 Quaoar

50000 Quaoar

Sum of 16 Hubble exposures registered on Quaoar.
Discovery[1] and Designation
Discovered by:	Chad Trujillo, Michael E. Brown
Discovery date:	June 4, 2002
Orbital characteristics[2]
Epoch October 22, 2004 (JD 2453300.5)
Aphelion distance:	6.716275 Tm (44.896 AU)
Perihelion distance:	6.270316 Tm (41.914 AU)
Semi-major axis:	6.493296 Tm (43.405 AU)
Eccentricity:	0.034
Orbital period:	104449.918 d (285.97 a)
Avg. orbital speed:	4.52 km/s
Mean anomaly:	273.737°
Inclination:	7.983°
Longitude of ascending node:	188.791°
Argument of perihelion:	154.850°
Physical characteristics
Dimensions:	1260 ± 190 km (direct)[3] 844+207−190 km (thermal)[4]
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 [3] 0.1986 +0.13−0.07 [4]
Temperature:	~43 K
Spectral type:	(moderately red) B-V=0.94, V-R=0.65
Absolute magnitude:	2.6

50000 Quaoar (pronounced kwaa'·waar or kwow'·ər, English IPA: [ˈkwɑ.wɑɹ], Tongva [ˈqʷɑoɑr]) [1] is a Trans-Neptunian object 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 creation deities (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.

Size

Quaoar is estimated to have a diameter of 1260 ± 190 km^[3], 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 2005 FY₉. 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^[3] 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)^[4].

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 2005 FY₉ 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.

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 Â°C (110 K or −260 Â°F) sometime in the last ten million years^[5]. Speculation began as to what could have caused Quaoar to heat up from its natural temperature of −220 Â°C (55 K or −360 Â°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^[6].

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)^[7].

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 [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^[8]. Assuming an albedo similar to that of the primary the magnitude suggests the diameter of 100 km.

References

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 science magazine
• 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

Minor planets
Previous minor planet	50000 Quaoar	Next minor planet
List of asteroids

•  • [ e] trans-Neptunian dwarf planets and candidates
Kuiper belt:	Orcus Pluto Ixion 2002 UX25 Varuna 2002 TX300 2003 EL61 Quaoar 2005 FY9 2002 AW197
Scattered disc:	2002 TC302 Eris 2004 XR190 Sedna
See also Triton, astronomical objects and the solar system's list of objects, sorted by radius or mass.  For pronunciation, see: Centaur and TNO pronunciation.

•  • [ e] Small Solar System bodies
Vulcanoids Near-Earth asteroids Main belt Jupiter Trojans Centaurs Damocloids Comets Trans-Neptunians (Kuiper belt • Scattered disc objects • Oort cloud) For other objects and regions, see , , Asteroid moons, meteoroids and the Solar System. For a complete listing, see List of asteroids. See also Pronunciation of asteroid names and Meanings of asteroid names.

•  • [ e] Trans-Neptunian objects
Plutinos	Pluto* |1993 SB| |1993 SC| 1994 JR1 |1994 TB| 1995 QZ9 1996 SZ4 1996 TP66 1996 TQ66 1997 QJ4 1998 HK151 1998 US43 1998 VG44 1998 WW24 1998 WU31 38083 Rhadamanthus 1999 TC36 38628 Huya 28978 Ixion 2002 KX14 2002 VR128 2003 VS2 90482 Orcus Unnumbered: 1993 RO 1993 RP 2003 AZ84 2001 QF298
Cubewanos:	1992 QB1 1994 GV9 1994 JQ1 1994 VK8 1995 SM55 1996 TO66 58534 Logos 1997 CS29 1997 CU29 1998 HJ151 1998 HP151 1998 HM151 1998 KR65 19521 Chaos 1998 WA25 1999 DF9 1999 HT11 53311 Deucalion 20000 Varuna 2002 AW197 50000 Quaoar 2002 TX300 2002 UX25 2003 EL61 2003 OP32 2004 GV9 2005 FY9 2005 RN43 Unnumbered: 1998 WW31 2002 MS4 2003 MW12 2003 QW90
Twotinos:	1996 TR66 1998 SM165 1999 RB216 2000 JG81 2002 WC19 Unnumbered: 1997 SZ10
Other Orbital Resonances:	|1994 JS| 1995 DA2 1998 WA31 1999 CP133 1999 DE9 1999 HB12 2001 KC77 2001 KP77 2002 TC302 2003 LG7
Scattered disc objects:	Eris* 1995 TL8 1996 GQ21 1996 TL66 1999 CC158 2000 EE173 2000 OO67 2000 OM67 2001 UR163 2002 CY224 2002 GX32 2002 RP120 90377 Sedna** 2005 RM43 2000 CR105 Unnumbered: 2004 XR190 2005 TN74 2006 QH181
Unclassified Objects:	1997 CR29 1998 SN165 1999 CL158 1999 HC12 1999 KR16 1999 OY3 2003 FY128 2004 SB60 2004 TY364 2005 RR43
Natural satellites:	Charon (Pluto) Hydra (Pluto) Nix (Pluto) Dysnomia (Eris) S/2000 (1998 WW31) 1 S/2005 (2003 EL61) 1 S/2005 (2003 EL61) 2 (58534) Logos I Zoe S/2005 (79360) 1
* - Also classified as a dwarf planet   ** - Currently classified as an SDO, though may be part of the Inner Oort Cloud