Large Kuiper Belt Objects.  Is 2003UB313 the tenth planet in the solar system?

Recently, Mike Brown et al. have discovered an object larger then Pluto, 97 astronomical units from the Sun (about 3 times Pluto's present distance).  This shows the large progress that has been made recently studying the outer solar system and raises many questions.  What else is out there?  It is possible that even larger objects exist far from the sun.  How were these objects formed, and how did they get in their present orbits?  How are they related to short period comets...?  and perhaps the question that has got the most attention in the popular press.  What is a planet?  How many planets does the solar system have?  Is 2003UB313 a planet?  is Pluto really a planet...?

Mike Brown has a page about some of his recent discoveries
http://www.gps.caltech.edu/~mbrown/
In particular the discovery paper for  2003UB313 is at
http://www.gps.caltech.edu/~mbrown/papers/ps/xena.pdf
and the paper showing that it has a moon,
http://www.gps.caltech.edu/~mbrown/papers/ps/gab.pdf

In 2006 the New Horizons spacecraft is scheduled to launch to explore Pluto and the Kuiper Belt.  Note the craft will not reach Pluto until 2015.
http://pluto.jhuapl.edu/

Finally a page with lots of information of the Kuiper Belt is
http://www.ifa.hawaii.edu/~jewitt/kb.html