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This article is from the In-Depth Report Hubble at 20: An Astronomical Success

Astronomers Discover Icy World Far Past Pluto

Quaoar



NASA/ G. BACON
Astronomers have discovered the largest object in the solar system since Pluto was identified more than 70 years ago. The object, dubbed Quaoar (pronounced "kwa-whar") by its discoverers, is approximately half Pluto's size and nearly four billion miles away from Earth. Scientists announced its discovery on Monday at the meeting of the Division of Planetary Sciences of the American Astronomical Society.

Michael Brown and Chadwick Truillo of the California Institute of Technology first discovered Quaoar in June while they were surveying the Kuiper Belt, the field of comet-like bodies stretching seven billion miles beyond Neptune's orbit, using a 1.2-meter telescope. It appeared as a point of light creeping across the constellation Ophiuchus. The researchers then used the Hubble Space Telescope to measure the object's 1,300-kilometer diameter. The icy rock reflects just 10 percent of the light that hits it and moves around the sun in a circular path once every 288 years. Brown and Truillo chose the name Quaoar from creation mythology of the Native American Tongva tribe, early inhabitants of the Los Angeles area, but the object has not yet been officially christened. Until the International Astronomical Union (IAU) votes on the moniker, the body's designation is the somewhat less flashy 2002 LM60.

Discovering Quaoar, the scientists say, fuels hope that more large-scale bodies will be found in the Kuiper Belt--perhaps even some larger than Pluto. As it stands, several hundred so-called Kuiper Belt Objects (KBO) have been identified since 1992. According to Brown, Pluto is also a KBO. "Quaoar definitely hurts the case for Pluto being a planet," he says. "If Pluto were discovered today, no one would even consider calling it a planet because it's clearly a Kuiper Belt Object."

"The Kuiper Belt," by Jane X. Luu and David C. Jewett (Scientific American, May 1996), is available for purchase from the Scientific American Archive.
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