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Large New World Discovered Beyond Neptune
By Robert Roy Britt
Senior Science Writer
posted: 29 July 2005
11:08 am ET


A newfound object in our solar system's outskirts may be larger than any known world after Pluto, scientists said today.

It also has a moon.

Designated as 2003 EL61, the main object in the two-body system is 32 percent as massive as Pluto and is estimated to be about 70 percent of Pluto's diameter.

Other news reports that the object could be twice as big as Pluto are false, according to two astronomers who found the object in separate studies and another expert who has analyzed the data.


Where it fits in

This is still a big world, once again raising the prospect that something larger than Pluto might still lurk out there.

Scientists base their size calculations in part on the object's reflectivity. Since they don't know exactly how much the surface brightness of distant objects varies, there is some wiggle room in their size estimates.

Is there any chance it is bigger than Pluto?

"No," Brown said in a telephone interview. "Definitely not."

In fact, Brown's team got the new data they had been waiting for, from the Spitzer Space Telescope, last week. While not fully analyzed, he said the Spitzer observations show "absolutely" that the object is not bigger than Pluto.

Marsden, of the Minor Planet Center, said it is surprising the object was not discovered earlier. He said it was probably just barely too faint to be spotted in the sky survey done by Clyde Tombaugh that led to the discovery of Pluto 75 years ago.

Brown's team first spotted 2003 EL61, which had no name at the time, using the Samuel Oschin Telescope at Palomar Observatory on May 6, 2004. They did not realized they had found it until Dec. 28, 2004, after scrutinizing their data in and ongoing effort to find Kuiper Belt Objects.