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SCIENCE & SPACE

Scientists: New 'planet' bigger than Pluto

Findings bolster support for 10th planet

story.2003.ub313.jpg
An artist's concept of 2003 UB313, an icy body that lies beyond the planet Neptune.

FACT BOX

THE NAME GAME

Many people say the sentence (called a mnemonic) "My Very Educated Mother Just Showed Us Nine Planets" as a way to remember the order of the planets.

Starting from the sun the planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

If 2003 UB313 is dubbed a planet, what new sentence will we use to remember it?

Source: NASA

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(CNN) -- German astrophysicists have concluded a space body located in the outer reaches of the solar system has a diameter 435 miles (700 kilometers) larger than Pluto, the smallest planet.

Their research puts more pressure on the International Astronomical Union (IAU) to classify the object as the 10th planet in our solar system.

"UB313 is decidedly larger than Pluto," said University of Bonn Professor Frank Bertoldi, whose team's findings will be published in Thursday's journal Nature.

The object, tentatively named 2003 UB313, is an icy body that lies beyond the planet Neptune.

2003 UB313 was first photographed in October 2003 by astronomers at the California Institute of Technology's Palomar Observatory, north of San Diego. Astronomers announced last summer that it was large enough to be a planet and was likely much larger than Pluto. (Full story)

To determine 2003 UB313's size, the Bonn team lead by Bertoldi and the Max Planck Institute for Radio Astronomy, used a Spanish telescope equipped with a sensitive heat sensor to measure its thermal emission.

Solar system objects are visible through the light they reflect from the sun. The bigger the planet, the bigger the reflection.

The report says "UB313's surface is such that it reflects about 60 percent of the incident solar light, which is very similar to the reflectivity of Pluto."

"Measuring the heat radiation of UB313 at a wavelength of 1.2 mm, where reflected sunlight is negligible and the object brightness only depends on the surface temperature and the object size, the temperature can be well estimated from the distance to the sun, and thus the observed 1.2 mm brightness allows a good size measurement."

Scientists determined 2003 UB313's diameter is about 1,864 miles (3,000 kilometers), which is 435 miles (700 kilometers) larger than Pluto.

"It is now increasingly hard to justify calling Pluto a planet if UB313 is not also given this status," Bertoldi said.

The claims of a 10th planet have re-ignited a debate over just how many objects should be called planets -- there is no official definition.

A number of astronomers dispute whether Pluto, discovered in 1930, should really be classified as a planet, because it is so dissimilar from the other eight planets in our solar system. They believe Pluto should be classified only as a Kuiper Belt object, part of an array of icy debris left from the formation of our solar system some 4.5 billion years ago.

The IAU, the official arbiter of such disputes, has classified Pluto as a planet and declined to demote it.

"The discovery of a solar system object larger than Pluto is very exciting," said the Planck Institute's Dr. Wilhelm Altenhoff. "It tells us that Pluto, which should properly also be counted to the Kuiper Belt, is not such an unusual object."

Thousands of Kuiper objects have been discovered, and more are being found all the time. The New Horizons spacecraft, launched on January 19, is on a 10-year journey to explore Pluto, its moons and the Kuiper Belt. (Full story)

2003 UB313's elongated orbit is 97 times as far from the Earth as the Earth is from the sun, or nearly 9 billion miles away.

Scientists measure the distances between planets in astronomical units (AU). One AU is the distance from the sun to the Earth -- 93 million miles (150 million kilometers). 2003 UB313 is 97 AUs from the sun.

Should 2003 UB313 be classified as a planet, its name will certainly change. The scientists who discovered it will submit a name, with the Astronomical Union making the final decision.

"I keep on talking about my object as that thing we found or 2003 UB313, which is a horrible name," said Mike Brown, a Cal Tech planetary scientist who discovered the object with colleagues Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University.

"It can't get an official name until it has an official status and right now it doesn't have an official status, so it can't get a name," he said.

CNN Producers Sara Weisfeldt and Kate Tobin contributed to this report.

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