July 31, 2005
New planet discovered

Our little solar system has grown.

Astronomers have discovered an object in our solar system that is larger than Pluto. They are calling it the 10th planet, but already that claim is contested.

The new world's size is not at issue. But the very definition of planethood is.


The new object, temporarily named 2003 UB313, is about three times as far from the Sun as is Pluto.

"It's definitely bigger than Pluto," said [Mike] Brown, a professor of planetary astronomy [at Caltech]. The object is round and could be up to twice as large as Pluto, Brown told reporters in a hastily called NASA-run teleconference Friday evening.

His best estimate is that it is 2,100 miles wide, about 1-1/2 times the diameter of Pluto.


Some astronomers view it as a Kuiper Belt object and not a planet. The Kuiper Belt is a region of frozen objects beyond Neptune.

Pluto is called a Kuiper Belt object by many astronomers. Brown himself has argued in the past for Pluto's demotion from planet status, because of its diminutive size and eccentric and inclined orbit.

But today he struck a different note.

"Pluto has been a planet for so long that the world is comfortable with that," Brown said in the teleconference. "It seems to me a logical extension that anything bigger than Pluto and farther out is a planet."

Offering additional justification, Brown said 2003 UB313 appears to be surfaced with methane ice, as is Pluto. That's not the case with other large Kuiper Belt objects, however.

"This object is in a class very much like Pluto," he said.

NASA effectively endorsed the idea in an official statement that referred to 2003 UB313 as the 10th planet.

I don't have any real opinion about the nature of planethood. I just want to know what we're all supposed to do for a mnemonic once Mary Vincent Eats Many Jelly Sandwiches Under Ned's Porch becomes inoperative. Naming the new arrival "Xena" certainly won't make that task any easier, that's for sure.

Posted by Charles Kuffner on July 31, 2005 to Technology, science, and math | TrackBack

My Very Elegant Mother Just Served Us Nine Pickles doesn't work, either...

If they're right about the orbit of it, my big question is "will it crash into pluto before the sun goes supernova?"

Posted by: Michael on July 31, 2005 9:44 AM

Pluto's planethood was always bunk -- six or seven MOONS of other planets in the solar system are larger. This discovery falls, IMO, in the "who cares?" category.

Posted by: Scott on July 31, 2005 9:47 AM

This is a nice link from NASA on the discovery:


The important passage on body size:

"Even if it reflected 100 percent of the light reaching it, it would still be as big as Pluto," says Brown. Pluto is 1400 miles (2300 km) wide. "I'd say it's probably [about] one and a half times the size of Pluto, but we're not sure."

The size of the planet is further limited by NASA's Spitzer Space Telescope, which has already proved its mettle in studying the heat of dim, faint, faraway objects such as the Kuiper-belt bodies. Because Spitzer has been unable to detect the new planet, the overall diameter must be less than about 2000 miles (3200 km), says Brown.

Posted by: B. K. Oxley (binkley) on July 31, 2005 11:16 AM

In the first grade, my class was assigned to make a model of the solar system using construction paper.

All the cool kids only cut out 9 little paper circles. I cut out ten.

I explained to my teacher that I had seen on TV (in retrospect, probably a science fiction movie from the 1950s) that there was a Planet X.

She didn't really disagree, so much as think I was being cute.

Well now, clearly, I have been vindicated.

Posted by: Jim D on July 31, 2005 2:16 PM

Xena, Warrior Planet.

Posted by: Karl-T on July 31, 2005 5:58 PM

If Xena turned out to have a moon, would it be named Gabrielle?

Posted by: Michael Croft on July 31, 2005 10:27 PM

Interesting that this 10th planet made the news, but Sedna's discovery last year didn't.


At its closest to the sun, it is still 2.5 times farther away than Pluto, orbiting 12 times that distance at other points in the orbit.

Posted by: Tx Bubba on August 2, 2005 2:39 PM

haha! at last but, i got a concern. there was a discovery of a planet in 2002 and was called the 10th planet. Now this new discovered should be the 11th not 10th remember?

Posted by: weeton on May 2, 2006 2:28 PM