14 DAY TRIAL // Not such a long time ago Pluto was considered a freak of the outer solar system not just because of its elliptic orbit but also because of its moon Charon. Charon has formed in a very similar manner Earth's Moon is thought to have been formed. However, lately, astronomers start to discover that Pluto and Charon are not that unusual: three out of four of the largest bodies found in the Kuiper Belt have at least one moon.
"We're now beginning to realize that Pluto is one of a small family of similar objects, nearly all of which have moons in orbit around them," says Antonin Bouchez, a California Institute of Technology astronomer.
The mystery is that physicists have computed that out of the hundreds of Kuiper Belt objects (the Solar System's outer area - more details here), there is only an 11 percent chance for a planetoid to capture another body thus transforming it in its satellite. However, it is already known that three of the largest bodies have at least one moon. Thus, the astronomers assume the moons are not captured but have appeared in different process.
The astronomers are pretty sure that Pluto's main satellite, Charon, has formed as a result of a collision between Pluto and another body. This collision has rendered a large piece out of Pluto - the future Charon. This process is similar to the way Earth's Moon has appeared, though our moon most likely has formed out of a hot disk of material left in orbit after such a violent impact.
The largest Kuiper Belt object, 25 percent larger than Pluto, is nicknamed Xena and it is known it has at least one moon. The second object in size is Pluto, which has three moons. The third is nicknamed "Santa" because it has been found around Christmas, and it has two moons.
"Santa is an odd one," says Bouchez. "You normally would expect moons to form in the same plane because they would have accreted from a disk of material in orbit around the main body. But Santa's moons are 40 degrees apart. We can't explain it yet."
Finally, the forth largest body from the Kuiper Belt is nicknamed "Easterbunny" because it was found around Easter. Insofar no moon has been found around this body, but Mike Brown's team, the discoverers of the three masive Kuiper Belt objects, plans to look for them in April using Keck's 10-meter telescopes.