CalTech astronomers Michael E. Brown and Chadwick Trujillo have announced the discovery of a spherical body 800 miles in diameter orbiting in the Kuiper Belt of our solar system, where Pluto resides. The body has tentatively been dubbed Quaoar after a Native American diety. It's not considered a new planet (it's too small), but it's the largest object detected in the solar system in seven decades. The last one was Pluto, which itself has had a tenuous grip on planethood. Here's the NY Times piece.