'Tenth Planet' really could be a planet
The controversy surrounding the 'Tenth Planet', 2003UB313, has deepened since the size of the object has been found to be larger than that of Pluto, the ninth 'official' planet. 2003UB131 has been found to be approximately 3,000 km across. Pluto is 2,300 km across. The body should be at least the size of Pluto in order to qualify for 'planet' status, although some critics believe that even Pluto should not qualify for planet status, as it, too, is simply too small. To put this into perspective, our own moon is larger than both bodies, at 3,500 km across. 'Since UB313 is decidedly larger than Pluto, it is now increasingly hard to justify calling Pluto a planet if UB313 is not also given this status,' said Professor Frank Bertoldi from the University of Bonn and the Max Planck Institute, who led the team. 'I would not want to demote Pluto for historical and cultural reasons - you'd upset the schoolchildren. So, it seems only fair to call objects larger than Pluto planets as well. I think we could cope.' The team used the Spanish Pico Veleta 30m Iram telescope located in the Sierra Nevada. They measured the size of UB313 by looking at its relative brightness. If they assumed that UB313 and Pluto were the same distance away from the Sun, then UB313 is brighter. Since UB313 is more than twice the distance from the Sun compared to Pluto, it must be larger. The team also assumed the temperature and reflectivity of the planet - a highly reflective, extremely frozen -248 degrees Celsius - similar, but somewhat colder than, Pluto. The absolute size is not yet established, however, as the surface, and therefore the reflectivity of UB313, is not yet known. This gives a margin or error of up to 400 km in diameter either way, meaning that if UB313's size was corrected downwards, it is still larger than Pluto. UB313 was first discovered by Michael Brown from the California institute of Technology in July 2005. He is pushing for the body to be established as a planet, and he refers to it as 'Xena', taken from the TV programme of the same name, and its moon 'Gabrielle'. If planet status is awarded, the name will be taken from Classical mythology. The International Astronomical Union (IAU) set up a committee to decide a workable definition of a planet, but the group folded in November 2005 without a good answer. Both Pluto and UB313 are within an area known as the Kuiper belt, which could hold up to one million objects of varying size. This area is beyond Neptune, and the reason why Pluto's status is disputed - it could simply be another Kuiper object - as could UB313. If more large Kuiper objects are discovered, they could all in theory be given planet status. 'You could have a distinction that says 'everything bigger than Pluto is a planet',' says Professor Iwan Williams from Queen Mary University in London, who will present working group options to the IAU in August. 'But then you are in danger of finding four or five of these objects in the next few years and you end up asking yourself, 'did we really mean to create 15 planets?' Perhaps we should just sit back and relax and see what else is discovered out there in the near future,' he said. Pluto was discovered in 1930 by astronomer Clyde Tombaugh. It has been controversial ever since its discovery as it has an irregular orbit, at a distinct angle to the orbits of the other planets, and it is sometimes closer to the Earth than Neptune. 2003UB313 shares some of these characteristics - it also has an irregular orbit and its closest proximity to the sun (perihelion) is roughly equal to Neptune's orbit.
Countries
Germany, Spain