Playful Pluto

As you probably know, a 10th planet (called UB313, or Xena) was discovered (not too) recently in our very own Solar System, but beyond Pluto. The reason that it has evaded our eyes till now is that its orbit forms quite an angle with the rest of the planets (with the first 8 at least, since Pluto's orbit is not aligned with us either.)
Actually lots of stuff are discovered beyond Pluto everyday, but the important thing about UB313 is that it's slightly larger than Pluto!
The discussion whether Pluto itself should be considered a planet has been going on for some time now. There are many things wrong with Pluto (or at least irregular) :
First, it has a very large (relatively) satellite, named Charon (pronounced kay-ron) with a diameter more than half of the diameter of Pluto, and a mass about 1/9 of that of Pluto. This ratio of mass causes the center of rotation of the Pluto-Charon system to be somewhere outside of both of them. Therefore, neither of them revolves around the other.
As a comparison, the mass of Earth's Moon is 1/80th of the mass of the Earth. This means that the center of rotation of the Earth-Moon system is 1/80th of the way along the line that connects their centers. Since this distance is ~400'000km, and Earth is the bigger object here, this point would be at about 400'000/80 (or 5000) km from the center of the earth. Again, as you all know Earth's radius is ~6300km, so the center of the Earth-Moon system is well inside the Earth, and Moon undoubtedly revolves around us. Also, have in mind that Moon is really big relative to Earth compared to other planet's satellites.
Let's go back to Pluto now. The second thing about Pluto is it's orbit. Not only it forms an angle with the plain that all other planets' orbits more or less lie on, it's a longer ellipse than typical for other planets. The orbit is so far from a circle that during a portion of its year, Pluto actually gets nearer to Sun than Neptune!
The third issue with Pluto is its size. Pluto is the smallest of all the 9 planets. It's diameter (2300km) is far smaller than Mercury's (4900km,) the second small planet in the Solar System. What's more annoying is that Pluto is actually smaller than Triton (Neptune's moon,) Titan (Saturn's,) Callisto, Europa, Ganymede and Io (all Jupiter's) and even our very own Moon! (It might be interesting to know that Ganymede and Titan are even larger than Mercury, but who dares touch Mercury?)
And now this UB313 business. That's why last month (August 2006) the International Astronomical Union changed the definition of "planet" so that it no longer included Pluto or UB313. They are called "dwarf planets" now and I think Ceres (a 1000-km asteroid!) and Charon are included in the definition. Of course, this redefinition, like any other radical change, is the subject of heavy controversy.
In any case, for now, the Solar System has 8 planets!