Quaoar (2002 LM60)
Quaoar (2002 LM60) |
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Greg Bacon, STScI, NASA --
larger illustration and
discovery images
("Quaoar," 2002 LM60, is one of the largest known EKOs
-- more).
Breaking News
According to astronomer Mike Brown's blog entry for December 31, 2007, Quaoar has a tiny moon. The satellite appears to be a remnant of an ancient collision with another large planetary body, much as the Earth's Moon is a remnant of a collision between a Mars-sized object and the Earth around 4.5 billion years ago. Brown hypothesizes that this giant collision should have removed most of the ice inside of Quaoar so that its interior should be much more rock than ice (as may be the case for many other large bodies recently found beyond the orbit of Neptune). If Quaoar is heavy and rock-like, its moon will be pulled along more quickly than if Quaoar has more ice and is lighter. As Brown can test his prediction by determining how much Quaoar weighs and seeing if its weight is more rock-like than ice-like, he wrote a proposal asking to use the Hubble Space Telescope to track its moon which has been accepted, and observations are now scheduled for sometime in Spring 2008 (more).
Quaoar
On October 7, 2002, astronomers Chad Trujillo and Mike Brown announced the discovery of one of the largest planet-like objects since Pluto was found in 1930. Identified as a new object on June 4, 2002, it was actually imaged as early as 1982 by astronomer Charles T. Kowal. Provisionally designated as 2002 LM60, the IAU eventually accepted the discovery team's nomination of "Quaoar" (the great force of nature that summoned all other things into being for the Tongva people who inhabited the Los Angeles area of the United States before the arrival of the Spanish and other European settlers) as a permanent name. On August 24, 2006, the International Astronomical Union (IAU) voted to establish a new category of Solar System objects called "dwarf planets." Quaoar (2002 LM60) is large enough to have a spherical shape and so is a candidate for IAU designation as a dwarf planet.
Ann Feild, STScI,
NASA -- larger image
(Quaoar is more than half as wide as
Pluto, the second largest known EKO --
more).
About 780 miles (1,250 km) in diameter, Quaoar has about one-tenth the diameter of Earth and more than half that of Pluto's, but is larger than Pluto's moon, Charon. As expected, Quaoar spins on its axis, but more visual data would have to be collected with the Hubble Space Telescope to determine its rate of spin. Located at an average orbital distance of about 43 AUs from the Sun, it moves in a roughly circular orbit (e~ 0.037) that is inclined by about 7.9° to the plane of the ecliptic and takes around 288 years to complete (more discussion of orbit in CalTech press release).
Ann Feild, STScI,
ESA,
NASA
Larger illustration.
Quaoar is one
of the largest
Solar System
objects found
beyond the orbit
of Neptune
since Pluto was
discovered in
1930
(more).
Quaoar is larger than the combined volume of the 50,000-some known rocky asteroids, but it may have only a third of their mass due to its high ice content. While Quaoar may be half composed of ices, it has a very dark surface and reflects only a little more than a tenth (a measured albedo of 12 percent) of the sunlight falling on it, as ultraviolet radiation over some 4.5 billion years has turned "organic" compounds on its surface into a dark tar-like substance. In contrast, Pluto reflects 60 percent of incident light off ices that evaporate and recondense on its surface as a whitish layer as it moves in an eccentric orbit that takes it closer to the Sun. (More discussion and animated illustrations at the Quaoar FAQ page, Space Telescope Science Institute, and Trujillo and Brown, 2002)
Other Information
Astronomer Chad Trujillo's discovery team maintains a Quaoar FAQ page.
More information and images of Pluto, Charon, and the Edgeworth-Kuiper Belt are available at NASA's Pluto-Kuiper Belt Mission and Planetary Photojournal. Fact sheets on Pluto and the Centaur object Chiron are also available from NASA's National Space Science Data Center.
David C. Hewitt has collected more images and information on Edgeworth-Kuiper objects at his Kuiper Belt Page.
David Seal (a mission planner and engineer at NASA's Jet Propulsion Laboratory at CalTech) has a web site that generates simulated images of the Sun, planets, and major moons from different perspectives and at different times of the year. Try his Solar System Simulator.
For more information about the Solar System, go to William A. Arnett's website on "The Nine Planets", or to Calvin J. Hamilton's web pages on "Kuiper Belt Objects" and "Pluto."
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