Moon discovered orbiting tenth planet
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The tenth planet in the solar system has a moon at least a tenth of its size. The discovery, made on 10 September with an adaptive optics system on the Keck II telescope, will allow astronomers to pin down the mass of both objects.The tenth planet is not officially a planet - for now its only official designation is 2003 UB313. By convention, its moon - announced by the International Astronomical Union on Sunday - is designated S/2005 (2003 UB313) 1.But Mike Brown, the Caltech astronomer who revealed 2003 UB313 in July and nicknamed it Xena after the television warrior princess, is calling the moon Gabrielle, after the princess's companion.Moons of "trans-Neptunian" objects - which orbit farther from the Sun than Neptune - are very hard to see because they are faint and appear very close in the sky to the objects they orbit. But Brown began searching for a moon as soon as he found 2003 UB313. "Having a moon is just inherently cool," he says.Moons can also reveal vital information about how a planet formed.
And astronomers can calculate the masses of both planet and moon by measuring the moon's orbit and period.So far Brown's group has only one night of observations of the moon, in which Gabrielle appeared as a faint dot 4.4 magnitudes fainter than Xena, moving with it across the sky. The moon is ten times closer to its planet that our Moon is to Earth, and the pair are 97 times further from the Sun than the Earth is. Viewed from Earth, they are separated by only half an arc-second.The best estimate of Xena's size so far is about 2700 kilometres in diameter, about one-fifth the size of the Earth. Gabrielle, which is about a tenth the size of Xena, is about one-eighth the size of our Moon.An intriguing consequence of the latest discovery is that three of the four largest objects beyond Neptune are now known to have moons, including Pluto and 2003 EL61.
http://www.newscientistspace.com/article/dn8086 -
THE solar system's newest and most remote object has been revealed to have a moon, although astronomers are divided over whether it really is a planet, as some believe it to be.
"Since the day we discovered Xena, the big question is whether or not it has a moon," said the California Institute of Technology's Michael Brown, whose team found both Xena, named after television's female warrior, and its moon.
"Having a moon is Â… something that most self-respecting planets have, so it is good to see that this one does too," he said. The moon, 100 times fainter than Xena and orbiting it once every couple of weeks, was spotted on September 10 by Hawaii's Keck telescope.
Xena is the temporary name of the planet, Gabrielle the temporary name of its moon. Professor Brown said the latest estimates for Xena, the solar system's most remote object, suggested it was 2700 kilometres across, compared with 2274 kilometres for Pluto, the smallest known planet.
Gabrielle is about 250 kilometres across. For some, such as Professor Brown, Xena's size earns it the title of planet. Others say that neither Xena nor Pluto should be classified as planets.
Originally contributed by ^tamago^