Tenth Planet

The tenth planet, if that's how it ends up being classed, is in the news again this week. A team of researchers has published a letter in Nature, reporting that its diameter is about half again as large as Pluto. Still more clearly a planet, even though so far away and with such an inclined orbit? Or will it inspire the demotion of Pluto and we'll end up with only 8 official planets?

2003 UB313 does not have a name yet. Its principal discoverer, Michael Brown of CalTech, calls it Lila; news stories call it Xenia or Santa. First its status (planet or no?) must be resolved, then it gets a real name. Which won't be any of the nicknames it has had so far.

Research on the far regions of the solar system beyond Neptune is one of the hot areas of astronomy right now. We have a quite informative book, Beyond Pluto : exploring the outer limits of the solar system by John Davies. Though it was published in 2001 and events have proceeded rapidly since then, it clearly describes research into the Kuiper Belt, the objects called Centaurs, the scattered disk objects, other sorts of far dim bodies. The original paper published by Brown, Trujillo and Rabinowitz in Astrophysical Journal formally announcing the discovery of 2003 UB313 is available online; and Brown has a very informative and more conversational webpage, The discovery of 2003 UB313, the 10th planet. There's a nice graphic of its orbit at Wikipedia.

At the moment, Xenia 2003UB313 is about 97 Astronomical Units from the Sun, that is, 97 times as far from the sun as earth is.