A billion miles away, the world of giant Quaoar is the frozen limit
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Your support makes all the difference.One billion miles beyond the solar system's most distant planet, four billion miles from the Sun, astronomers have discovered a massive object. "Quaoar" (pronounced kwah-o-wahr,) a frozen world measuring 800 miles across, is the biggest mass found orbiting the Sun since the discovery of Pluto in 1930.
Quaoar is "about the size of all the asteroids put together," said Michael Brown, associate professor of planetary astronomy at the California Institute of Technology in Pasadena. "So this thing is really big".
But it is unlikely to win the accolade of "planet". Even Pluto has struggled to hold on to that title. Quaoar orbits the Sun once in 288 years, and is about a tenth the diameter of Earth, half Pluto's size, though apparently larger than that planet's moon, Charon.
The discovery lies in the "Kuiper Belt", a distant swarm of ice and rock objects that orbit the Sun far beyond Neptune. They are reckoned to be leftovers from the process that formed the solar system five billion years ago. Many comets are believed to originate there, falling towards the Sun as their orbit becomes unstable. There is no risk that Kuiper objects will hit the Earth.
The belt contains as many as 10 billion objects at least one mile across; astronomers estimate five to 10 of those are as large as Quaoar (named after a creation force in southern Californian Indian mythology).
"This discovery fits with our expectation that there should be a handful or two of objects as large as Pluto," astronomer David Jewitt, of the University of Hawaii, said. Dr Jewitt, with then-colleague Jane Luu, discovered the first Kuiper Belt object a decade ago.
Unfortunately for the planet, this discovery weakens its case to be counted with larger siblings. In 1999, Pluto narrowly survived being downgraded from a "planet" to "minor planet" by the International Astronomical Union. Even the venerable astronomer Patrick Moore said: "Pluto cannot be classed as a bona fide planet."
One embarrassment for astronomers is that Quaoar could have been discovered 20 years ago. The Caltech scientists found it when they checked film archives going back to 1982.
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