MadSci Network: Astronomy |
There hasn't been a tenth planet discovered in our solar system. LOTS of astronomers have spent lots of time on various hunts for one, though. There's a huge page about it at http://dept.physics.upenn.edu/nineplanets/hypo.html#planetx
On the other hand, planets have been discovered in other solar systems. There's a list of all the candidates (over a dozen) at http://www.obspm.fr/departement/darc/planets/catalog.html But they're so far away that we couldn't send spacecraft to them in less than hundreds of years -- using today's technology, at least. Makes them less cool in my opinion since we can't see what they're like....
-Jim
Try the links in the MadSci Library for more information on Astronomy.