2003 UB313, or Xena, is currently thought to be about 2,000 miles across, which is a good bit bigger than Pluto. Pluto is only 1,450 miles across. However, it may take another 6 months to determine the exact size of Xena.

At its far distance from the sun, an average day’s temperature would be somewhere around minus 400 degrees F on Xena. Might be a great place to hold the next Winter Olympics?

It takes more than 204,000 days for the tenth planet, nicknamed Xena, to orbit the sun. That’s a long, long year, 558 of our years – or about 7 or 8 of our lifespans.

Dr Brown and his team have christened the planet, Xena, after the warrior princess in the old television series, “… because we always wanted to name something Xena”. But the formal decision on a name will be made by the International Astronomical Union.
I would love to see it named Xena, but we will have to [...]

The discoverers of the tenth planet are Michael E. Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University). They first imaged the object on October 21, 2003, but didn’t see it move in the sky until reimaging the same area 15 months later on January 8, 2005. They announced the discovery [...]

You can see a movie of the tenth planet showing its motion on the sky in 3.5 hours, created by Gianluca Masi at http://www.bellatrixobservatory.org/2003ub313.gif

The tenth planet is the farthest-known object in the solar system at about 9 billion miles away from the sun, and the third brightest of the Kuiper belt objects. Neptune probably flung it into its highly inclined (44°) orbit. It’s currently glowing at magnitude 18.9 in the constellation Cetus.

Like Pluto, the tenth planet’s surface is believed to be predominantly methane ice. More data may be presented in September by the US team. Methane ice is unusual and suggests a primitive surface that has never been warmed much since the formation of the solar system.

The new planet is believed to be part of the Kuiper Belt, a large ring of icy objects that orbit beyond Neptune and are believed to be remnants of the material that formed the solar system. Objects in the Kuiper Belt are believed to have had a close encounter with Neptune, which then scattered [...]

The tenth planet is approximately 87 astronomical units from the sun. An astronomical unit is the distance between the Earth and the sun.