22nd 23rd 24th 30th* largest object in our solar system, weighing in behind Saturn's moon Iapetus, but well ahead of Uranus' Umbriel.
Granted, if you aren't the sort of person that's really "up" on the whole tremendous-hunks-of-frozen-rock scene, the previous sentence probably meant about as much to you as two grandmas comparing heirloom tomatoes. But believe you me, when it comes to the truly hardcore frozen-rock fans, guys like CalTech's Chad Trujilo and Mike Brown, Quaoar is something of a big deal.
For one thing, Quaoar is a spheroid object approximately 1,250 kilometers wide. That alone is astounding. This makes Quaoar the single largest object found in our solar system since Tombaugh discovered Pluto, some 72 years ago. Astronomers Brown and Trujilo first spotted the object in June of this year, using the Oschin Telescope, a 122cm rig at the Mount Palomar Observatory in Southern California. Trujilo later commented that he was really surprised that no one else had seen it; "it is almost bright enough that a dedicated amateur could find it with a 16-inch lens." Of course, that naturally leads to another question, namely...
How the hell did we miss this before? Simply this: It's six and a half billion kilometers away, hanging on a tenous thread of attraction at the extreme edge of our gravity well, a neighborhood known as the Kuiper Belt. As such, it's been rotating around the sun at a leisurely 4.5 kilometers/second (about a sixth of Earth's speed), tracing its path around the sun only once every 288 years. And it's likely been doing it for billions of years now.
Quaoar is named after the creation diety of the Tongva nation, a Los Angeles band of Native Americans that were the original inhabitants of the land CalTech now occupies. This is appropriate, since one of the major theories about the Kuiper Belt is that it's the remnants of a much earlier epoch in our solar history, leftovers from the time when the planets were still forming. It is said that, at the dawn of time, Quaoar came down from heaven, and after reducing chaos to order, he laid out the world on the back of seven giants. He then created the lower animals, and finally, man.
Official designation: 2002 LM60
Official classification: Kuiper Belt Object
Discovered: June 4, 2002
Discovered by: Mike Brown/Chad Tujilo
Composition: Unknown (believed to be mostly rock and ice fragments)
Diameter: ~1250 km
Orbital Distance: 6.5 billion km
Orbital Period: 288 years
Spin Rate: Unknown
Spin Axis: 7.9 degrees
Albedo: 12 percent
Note that, with Quaoar coming hot on the heals of Ixion and Varuna-- similiarly massive objects found in the same region of space-- things are not looking good for Pluto. Aside from its lack of atmosphere and its enormous orbital period, Quaoar is in some ways more "planet-like" than what we're currently calling our ninth planet. Unlike Pluto's eccentric orbit, tilted 17 degrees off the orbital plane, Quaoar's path is much more regular and lined up closer to the elliptic. In the words of Mike Brown: "If Pluto was discovered today, no one would even consider calling it a planet."
It should also be noted that Quaoar was discovered as part of a Kuiper Belt survey program that is, at this moment, only 7% complete. Lord knows what else we'll find out there, floating around in our own backyard.
* Update 3/15/04: chalk up another one for Tujilo and Brown. NASA announced today that the intrepid stargazing pair, along with David Rabinowitz of Yale University, have discovered "Sedna" (2003 VB16), a Kuiper Belt object that dwarfs even Quaoar, with an estimated diameter between 1200 and 1800 kilometers, and which orbits the sun at an unimaginable 13 billion km.
Update 9/29/05 - Sedna has been one-upped yet again, by 2003 UB313 (aka Xena). Estimates suggest that Xena's diameter is 2700 kilometers or more, even larger than Pluto's 2400 kilometers. Like the others, it's being heralded as a "10th planet". Of course, by that logic we already *had* a 10th planet (The Moon), but that's a whole 'nuther can of worms.
Update 07/16/15 - Editor note - now we also have Haumea (136108 Haumea) and (225088) 2007 OR10.
Sol system objects arranged by diameter
National Geographic (http://news.nationalgeographic.com/news/2002/10/1003_021007_quaoar.html)
International Herald Tribune (http://www.iht.com/articles/73070.html)
Independent News UK (http://news.independent.co.uk/world/science_medical/story.jsp?story=340502)
CalTech 336 Online (http://pr.caltech.edu/periodicals/336/articles/Volume%205/09-22-05/planet.html)