Move over, Pluto

Move over, Pluto

Mona Chiang

It’s a fact of life, right? The solar system contains nine planets. Don’t be so sure. A growing number of scientists think it’s time to scratch Pluto from the lineup. “Scientifically it makes sense,” says planetary astronomer Mike Brown of the California Institute of Technology in Pasadena, Calif. Brown’s evidence? An icy rock-he and a colleague recently discovered. It orbits 6.4 billion kilometers (4 billion miles) from the Sun in Pluto’s neighborhood–a region of ice and rocks beyond Neptune’s orbit called the Kuiper Belt.

The discoverers have named the icy chunk Quaoar (KWAH-o-ar) after a Native American deity. At about 1,287 km (800 mi) in diameter, Quaoar is roughly half Pluto’s size. But it’s the largest object found orbiting the Sun since the first sighting of Pluto 72 years ago. “When Pluto was discovered, nobody knew this region existed,” says Brown. “There was nothing else to call Pluto, so everybody called it a planet.”

Today, bodies in this region are called Kuiper Belt objects, and scientists have tracked more than 600 so far. Planets are usually defined as large bodies orbiting a star. “Some argue Pluto is much larger than any Kuiper Belt object,” Brown says. “It’s only a little bit bigger than Quaoar, and I’m fairly convinced we may find something as large as Pluto–if not larger.” Only 5 to 10 percent of the Kuiper Belt has been studied. Clearly, the debate on Pluto is just beginning.

RELATED ARTICLE: New Neighbor to Pluto Discovered.

Astronomers have found the largest object in the solar system since the discovery of Pluto in 1930. The object, called Quaoar, (pronounced KWAH-o-ar), orbits the Sun every 288 years.

Quaoar is about 4 billion miles from the Sun, 1 billion miles farther than Pluto.

Like Pluto, Quaoar lies in the Kuiper Belt, a debris field of ice and rocks beyond the orbit of Neptune.


Quaoar: 1,287 kilometers (800 miles) in diameter

Pluto: 2,253 km (1,400 mi)

Earth’s moon: 3,380 km (2,100 mi)

Earth: 12,875 km (8,000 mi)

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