The spherical planetoid, half the size
of Pluto, is the biggest found in the solar system since astronomers detected the ninth planet in 1930.
It orbits the sun from a distance of
about 4 billion miles (6.4 billion kilometers) in a nether region known as the Kuiper Belt, a ring of thousands of primordial
icy, rocky chunks beyond the planets that date back to the origins of the solar system.
The object, dubbed Quaoar, further strengthens
the theory that Pluto is not a conventional planet but rather a Kuiper Belt object.
"Quaoar definitely hurts the case for
Pluto being a planet," said planetary scientist Mike Brown, co-discover of the new object. "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 is home to many of the
comets that periodically swing into the inner solar system. They and larger objects in the belt are pristine vestiges of the
infant solar system, which could help explain how our space neighborhood formed.
The new object is about 800 miles (1,300
kilometers) in diameter and circles the sun once every 288 years. Its orbit is stable and circular in comparison to Pluto.
Pluto, usually the most distant planet,
takes 248 years to complete a trip around the sun and orbits at an average distance of about 3.7 billion miles (5.8 billion
kilometers).
But the
eccentric ice planet follows an extremely elliptical orbit and goes inside the circular path of Neptune from time to time.
While traditionally classified as a
planet, Pluto more likely is a Kuiper Belt object that was pushed into an erratic, Neptune-crossing orbit billions of years
ago, according to astronomers.
Like other Kuiper Belt objects, Quaoar
is thought to contain rock, water ice and frozen organic compounds such as methane, carbon dioxide and carbon monoxide.
The surface, slowly cooked over the
eons by ultraviolet radiation from the sun, could be dark and similar in consistency to tar, Brown and co-discoverer Chad
Trujillo said.
The California Institute of Technology
researchers presented their findings Monday at an American Astronomical Society meeting in Birmingham, Alabama.
The scientific duo named the object
Quaoar, pronounced KWAH-o-ar, after the creation god of the Tongva people, a Native American tribe in Southern California.
As telescopes and high-tech search techniques
improve in the coming years, astronomers said they expect to find many more Kuiper Belt objects, including increasingly larger
specimens.
"Right
now, I'd say they get as big as Pluto," Brown said.
