Here's a brief bit from The Times Online:
"FAR OUT on the edge of the solar system, a new planet has been discovered — a lump of ice nine billion miles from the sun, orbiting at the stately rate of once every 560 years. The astronomical community is cooing over the new arrival, which was announced last month, weighing in with a diameter of some 3,000km and a surface temperature of minus 459F. But as with every newborn, there is a dilemma: scientists cannot agree about what (on earth) to call this tenth planet, the youngest —addition to the planetary family.
Currently, the planet still retains the official and unlovely moniker 2003UB313, a name that even its mother couldn’t love. The astronomer who discovered it, Mike Brown, of Caltech, nicknamed the lump Xena, after the semi-clad warrior princess of the American television series, and it has stuck. How is that for a reflection of our cultural impoverishment?"
Full article for those with a long concentration span:
Personally I think Xena and Loki are good names for it.