New claims of a tenth planet
Artist's impression of the distant object 2003UB313 which some claim is the tenth planet.
© NASA
Astronomers in the USA have discovered what they claim is the Solar system's tenth planet. The object, which has been given the name 2003UB313, is currently 97 astronomical units away, putting it more than twice Pluto's average distance from the Sun. This makes it the farthest object ever seen in the solar system. Although they cannot yet be sure, they think that 2003UB313 is a rocky object about one and a half times the size of Pluto - hence their claim for it being a planet.
However, since its discovery there has been some debate amongst other astronomers as to whether the new object can truly be called the tenth planet. The problem is that 2003UB313's orbit is highly inclined or tilted (44°) to the orbits of the other planets in the solar system - that is, all apart from Pluto which also has an inclined orbit (17°). The question then arises as to whether the object formed in the same way as the other planets or whether it is simply a large lump of rock that was somehow captured into its highly eccentric 557 year orbit around the Sun.
In truth there may be many similar planet-shaped objects orbiting our Sun well beyond the orbit of Pluto. More commonly known as Kuiper Belt objects, they exist in what is believed to be a vast 'shell' of icy and rocky objects that live at the very edge of our solar system. Similar objects have been discovered in recent years, such as Quaoar, Sedna and Orcus, which gave rise to similar tenth planet claims. In fact, many astronomers think that the discussion should now be as to whether Pluto should be de-classified as a planet, rather than the new object be accepted as a new one.
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