50000 Quaoar

50000 Quaoar

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50000 Quaoar is a rocky trans-Neptunian object
Trans-Neptunian object
A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...

 in the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...

 with one known moon. Discovered on June 4, 2002 by astronomers Chad Trujillo
Chad Trujillo
Chadwick A. "Chad" Trujillo is an astronomer and the co-discoverer of the dwarf planet Eris.Trujillo works with computer software and has examined the orbits of the numerous trans-Neptunian objects , which is the outer area of the solar system that he specialized in. In late August 2005, it was...

 and Michael Brown
Michael E. Brown
Michael E. Brown has been a professor of planetary astronomy at the California Institute of Technology since 2003....

 at the California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...

 from images acquired at the Samuel Oschin Telescope
Samuel Oschin telescope
The Samuel Oschin telescope is a 48-inch aperture Schmidt camera at the Palomar Observatory in northern San Diego County, California. It consists of a 49.75-inch Schmidt corrector plate and a 72-inch mirror. The instrument is strictly a camera; there is no provision for an eyepiece to look...

 at Palomar Observatory
Palomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...

, it is thought by Michael Brown to be "nearly certainly" a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

, although the IAU has not yet formally designated it as such.

Discovery


The discovery of Quaoar, a magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 18.5 object located in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Ophiuchus
Ophiuchus
Ophiuchus is a large constellation located around the celestial equator. Its name is from the Greek "serpent-bearer", and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century...

, was announced on October 7, 2002, at a meeting of the American Astronomical Society
American Astronomical Society
The American Astronomical Society is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC...

. The earliest prediscovery image
Precovery
Precovery is a term used in astronomy that describes the process of finding the image of an object in old archived images or photographic plates, for the purpose of calculating a more accurate orbit...

 proved to be a May 25, 1954 plate from Palomar Observatory. It may qualify as a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

, given its size inferred from direct observation by the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

.

Name


Quaoar is named for the Tongva creator god
Quaoar (mythology)
Quaoar is the creation deity of the Native American Tongva people, native to the area around Los Angeles, California. According to Tongva mythology, Quaoar sings and dances the world and other deities into existence....

, following International Astronomical Union
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

 naming conventions
Planetary nomenclature
Planetary nomenclature, like terrestrial nomenclature, is a system of uniquely identifying features on the surface of a planet or natural satellite so that the features can be easily located, described, and discussed. The task of assigning official names to features is taken up by the International...

 for non-resonant Kuiper belt objects. The Tongva are the native people of the area around Los Angeles
Los Angeles, California
Los Angeles , with a population at the 2010 United States Census of 3,792,621, is the most populous city in California, USA and the second most populous in the United States, after New York City. It has an area of , and is located in Southern California...

, where the discovery of Quaoar was made. They 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 . 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
20000 Varuna
20000 Varuna is a large classical Kuiper belt object and a probable dwarf planet. It previously had the provisional designation ' and has been precovered in plates dating back to 1953.-Name:Varuna is named after the Hindu deity,...

. However, later even larger discoveries were simply numbered according to the order in which their orbits were confirmed.

Size


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
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

 since the discovery of Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

. Quaoar was later supplanted by , , , and . In addition, the subsequently discovered plutino
Plutino
In astronomy, a plutino is a trans-Neptunian object in 2:3 mean motion resonance with Neptune. For every 2 orbits that a plutino makes, Neptune orbits 3 times. Plutinos are named after Pluto, which follows an orbit trapped in the same resonance, with the Italian diminutive suffix -ino...

  is about the same size as Quaoar but Quaoar is 2½ times as massive, about as massive as (if somewhat smaller than) Pluto's moon Charon
Charon (moon)
Charon is the largest satellite of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory Flagstaff Station. Following the 2005 discovery of two other natural satellites of Pluto , Charon may also be referred to as Pluto I...

. Quaoar is roughly one fifteenth the diameter of Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, one quarter the diameter of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

, and a third the size of Pluto.

Quaoar was the first trans-Neptunian object
Trans-Neptunian object
A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...

 to be measured directly from Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 (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
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....

) 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
Point spread function
The point spread function describes the response of an imaging system to a point source or point object. A more general term for the PSF is a system's impulse response, the PSF being the impulse response of a focused optical system. The PSF in many contexts can be thought of as the extended blob...

 (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
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 measurements by the Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...

 which suggest a brighter albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 (0.19) and consequently a smaller diameter (844.4 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
Limb darkening
Limb darkening refers to the diminishing of intensity in the image of a star as one moves from the center of the image to the edge or "limb" of the image...

 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.

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 4.2 g/cm3 and estimated size of 890 km suggests that it should qualify as a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

 if the mass required for hydrostatic equilibrium
Hydrostatic equilibrium
Hydrostatic equilibrium or hydrostatic balance is the condition in fluid mechanics where a volume of a fluid is at rest or at constant velocity. This occurs when compression due to gravity is balanced by a pressure gradient force...

 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 around 400 km. With an estimated mass greater than 1.3 kg, Quaoar probably has the mass required (5 kg) for being considered a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...

 under the 2006 IAU draft definition of a 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
Erik Ian Asphaug
Erik Ian Asphaug born October 19, 1961, in Oslo, Norway) is a Norwegian American planetary science professor at the University of California, Santa Cruz. Asphaug received his bachelor's degree in mathematics and English from Rice University and his PhD in planetary science from the University of...

 has suggested that Quaoar may have collided with a small planet up to the size of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

, 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, possibly Pluto itself.

Orbit





Quaoar orbits at about 43 AU from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 with an orbital period of 286 years.

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
20000 Varuna
20000 Varuna is a large classical Kuiper belt object and a probable dwarf planet. It previously had the provisional designation ' and has been precovered in plates dating back to 1953.-Name:Varuna is named after the Hindu deity,...

, , and are all on highly inclined, more eccentric
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...

 orbits.

Quaoar is the largest body that is classified as a cubewano
Cubewano
A classical Kuiper belt object, also called a cubewano is a low-eccentricity Kuiper belt object that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40–50 AU range and, unlike Pluto, do not cross Neptune’s orbit...

 by both the Minor Planet Center
Minor Planet Center
The Minor Planet Center operates at the Smithsonian Astrophysical Observatory , which is part of the Center for Astrophysics along with the Harvard College Observatory ....

 and the Deep Ecliptic Survey
Deep Ecliptic Survey
The Deep Ecliptic Survey is a project to find Kuiper belt objects , using the facilities of the National Optical Astronomy Observatory .The principal investigator is Bob Millis....

.

The polar view compares the near-circular Quaoar's orbit to highly eccentric (e=0.25) orbit of (Quaoar’s orbit in blue, Pluto’s in red, Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

 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
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...

 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
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 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 , 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 . The albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

 could be as low as 0.1, which would still be much higher than the lower estimate of 0.04 for . 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
20000 Varuna
20000 Varuna is a large classical Kuiper belt object and a probable dwarf planet. It previously had the provisional designation ' and has been precovered in plates dating back to 1953.-Name:Varuna is named after the Hindu deity,...

 and 28978 Ixion
28978 Ixion
28978 Ixion is a Kuiper belt object discovered on May 22, 2001. Ixion is a plutino and a very likely dwarf planet; its diameter of 650 km estimated by Spitzer makes it about the fifth largest plutino. It is named after Ixion, a figure from Greek mythology...

 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).


Cryovolcanism


In 2004, scientists were surprised to find signs of crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 on Quaoar, indicating that the temperature rose to at least −160 °C (110 K or −260 °F) sometime in the last ten million years.

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-meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...

s may have raised the temperature, but the most discussed theory speculates that cryovolcanism
Cryovolcano
A cryovolcano is a volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock. Collectively referred to as cryomagma or ice-volcanic melt, these substances are usually liquids and form plumes, but can also be in vapour form...

 may be occurring, spurred by the decay of radioactive elements within Quaoar's core.

Since then (2006), crystalline water ice was also found on , but present in larger quantities and thought to be responsible for the very high albedo of that object (0.7).

More precise (2007) observations of Quaoar's near infrared spectrum indicate the presence of small (5%) quantity of (solid) methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 and ethane
Ethane
Ethane is a chemical compound with chemical formula C2H6. It is the only two-carbon alkane that is an aliphatic hydrocarbon. At standard temperature and pressure, ethane is a colorless, odorless gas....

.
Given its boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 (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
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

, ) can retain the volatile ices while the dominant population of small TNO
TNO
TNO can stand for:* Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek * Trans-Neptunian object* Tamarindo Airport in Tamarindo, Costa Rica...

s lost them. Quaoar, with only small amounts of methane, appears to be in an intermediary category.

If the New Horizons
New Horizons
New Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...

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



Quaoar has one known satellite, Weywot
Weywot (moon)
Weywot, officially Quaoar I Weywot, is the only known moon of the trans-Neptunian object Quaoar. Its discovery was reported in IAUC 8812 on 22 February 2007, based on imagery taken on 14 February 2006. The satellite was found at 0.35 arcsec from Quaoar with an apparent magnitude difference of 5.6...

, 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
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 difference of 5.6. It orbits at a distance of 14,500 km from the primary and has an orbital eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...

 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.

Brown left the choice of a name up to the Tongva, who chose the sky god Weywot
Weywot
Weywot is the sky god of the Tongva people, son and first creation of the creator god Quaoar. The Tongva chose the name Weywot for the moon of the likely dwarf planet , which was named after their creation god.-External links:*...

, son of Quaoar. The name was made official in MPC #67220 published on October 4, 2009.

External links