for National Geographic News
Astronomers announced today the discovery of the largest object in the solar system since Pluto was named the ninth planet in 1930. The object is half the size of Pluto, composed primarily of rock and ice, and circles the sun once every 288 years.
Named Quaoar (pronounced KWAH-o-ar), the object resides in the Kuiper belt, a region of the sky beyond the orbit of Pluto and about 4 billion miles (6.5 billion kilometers) from Earth. The Kuiper belt is chock full of remnants from the planet-formation era of the solar system.
Scientists study the Kuiper belt to understand what the solar system was like when it formed. They have theorized for several years that objects the size of Quaoar and bigger exist in the region, but until now had not detected anything quite so large.
"My first reaction was 'wow, that is a bright object and looks like it could be really big,'" said Chad Trujillo, a researcher at the California Institute of Technology in Pasadena.
"My second reaction was I wonder why no one has seen this before. It is almost bright enough that a dedicated amateur could find it at a dark site with a 16-inch [41-centimeter] telescope."
Trujillo is working with colleague Mike Brown to survey the Kuiper belt with the 48-inch (122-centimeter) Oschin Telescope at the institute's Palomar Observatory. The telescope is equipped with a charge-coupled device (CCD—the same technology used in digital cameras), which is sensitive to faint objects.
The discovery of Quaoar was announced today at the meeting of the Division of Planetary Sciences of the American Astronomical Society in Birmingham, Alabama.
"Quaoar is an awesome object that fits well with the existing picture of the Kuiper belt," said Dave Jewitt, a professor at the University of Hawaii's Institute for Astronomy in Honolulu and an expert in the study of Kuiper belt objects.
Sizing Up Quaoar
Since Quaoar was discovered on June 4, the researchers have measured it with a heat-sensitive telescope at the International Institute for Research in Millimeter Astronomy (IRAM) in France and the Hubble Space Telescope.
The 98-foot (30-meter) IRAM telescope measures the amount of heat emitted by an object. Larger objects emit more heat. This measurement is combined with an optical measurement to determine size.
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