New object deemed largest minor planet

An ESO observatory in Chile captured the planetoid in this composite image.

By Richard Stenger
CNN

(CNN) -- An icy body beyond Pluto has unseated the asteroid Ceres as the largest minor planet in the solar system, breaking a record that stood for two centuries, European astronomers announced this week.

The frozen rock has a diameter of at least 1,200 kilometers (745 miles), much larger than the old titleholder, a colossal boulder discovered in 1801 by Italian astronomer Giuseppe Piazzi.

Ceres, which resides in the main asteroid belt between Mars and Jupiter, has a diameter of about 950 kilometers (590 miles).

The new object is half the size of Pluto and slightly larger than Pluto's moon Charon. It orbits the sun in a ring of primordial comets beyond the planets known as the Kuiper Belt.

Pluto, while officially classified a planet, is now considered by many astronomers as a Kuiper Belt Object, as is Charon.

Hundreds of Kuiper Belt Objects have been discovered. Astronomers theorize that tens of thousands more lurk in the dark recesses of the solar system, some perhaps rivaling Pluto in size.

"There have many predictions about bigger Kuiper Belt Objects. Now we are starting to see them. I think we are going to start seeing many more big ones out there," said Richard West, an astronomer with the European Southern Observatory, which established the size of the new object, known as 2001 KX76.

Kuiper Belt Objects, among the most primitive objects known, are thought to be pristine relics of the formation of the solar system.

What is in a name?

Relative sizes of the largest known bodies in the outer solar system.

In July, U.S. astronomers first spotted 2001 KX76 and tentatively estimated that it rivaled Ceres in size.

European Southern Observatory scientists, crunching data from numerous telescopes in a "virtual observatory," plotted the orbiting path of the object for the past 18 years, which helped produce the more authoritative diameter measurement: between 1,200 and 1,400 kilometers (745 and 870 miles).

The estimate is conservative and later refinement could determine that it is larger, West said.

The object, which has an elliptical orbit much like Pluto, is about 6.45 billion kilometers (4 billion miles) from the sun, or 43 times the distance between the Earth and sun.

Its title secure, 2001 KX76, should soon receive a more appealing name from the original discoverers. Custom maintains that Kuiper Belt Objects be given mythological names associated with creation.

The next largest known Kuiper Belt Object, Varuna, has an estimated diameter of 900 kilometers (560 miles). It was named for the Vedic god of oceans and water.