2003 UB313 was announced on 29 July 2005 after two years of observations showed it to be the largest known member of the Kuiper Belt, larger even than Pluto, causing NASA to designate the object as the tenth planet of our solar system in its discovery press release. Best estimates are that the new object has a radius 1.25 times that of Pluto. Radius estimates of KBOs are determined based on brightness and distance, but can be skewed by the object's albedo. If 2003 UB313 has a higher albedo than other KBOs, then it would be smaller than current estimates suggest. Still, the discoverers state that even if the albedo of 2003 UB313 is 100%, which is very unlikely, the new object would still be as large as Pluto. So if Pluto is a planet, so is 2003 UB313. Currend radius estimates are based on the assumption that the new planet's albedo is around 60%, like Pluto, due to the fact the its spectrum is very similar to Pluto's. The discoverers attempted to find the object with the Spitzer Space Telescope but were unable to detect it due to a technical glitch. Another detection attempt with Spitzer is underway. At the time of the announcement, 2003 UB313 was at 19th magnitude in the constellation of Cetus. It is observable with large backyard telescopes and amateur astronomers were photographing it only hours after the discovery was announced. In fact, if the new planet wasn't orbiting at such a high inclination, 44º to the plane of the ecliptic, it is very probable that it would have been discovered years ago. 2003 UB313 appears to be a scattered-disk object and was probably tossed into its highly inclined orbit by the planet Neptune sometime in the distant past. Near infrared observations of the new planet indicate a surface dominated by methane ice, much like Pluto. In fact, of all the KBOs only Pluto and Neptune's moon Triton share this strong methane signature. A name for the new planet has been submitted to the IAU but will only be announced when it is approved. The directory of the discoverer's website was /planetlila, suggesting to many that the new name would be "Lila" after the discoverer's newborn daughter, but this is apparently not the case. Apparently the planet has been nicknamed "Xena" by the discoverers after the main character of the TV show of the same name. It is not known if this is the name they have submitted to the IAU. Even before the announcement of 2003 UB313, controversy existed over the definition of a planet. Observations of the Kuiper Belt have turned up many objects, like Varuna, Quaoar, and Sedna, that are two-thirds to one half the size of Pluto and some have suggested that these objects should be called planets. Others site Pluto's own membership in the Kuiper Belt as an indication that the ninth planet is not a planet at all. If 2003 UB313 is indeed larger than Pluto as current observations suggest, it brings home the need for a better definition of what a planet is. Certainly, if Pluto is a planet, then 2003 UB313 is one as well. But if Pluto is not a true planet, then perhaps 2003 UB313 is not one either. Some would even claim that 2003 UB313 is the ninth planet and demote Pluto. Recognizing the need for a better definition of "planet" in the wake of 2003 UB313's discovery, the IAU has recently announced that it will be releasing an official scientific definition of the term soon.
View a VRML model of the system. Please be patient while the file downloads. For a VRML tour of our galaxy's exoplanets, check out Extrasolar VR.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Current Planet
Habitability Zone
