Question: how many dwarf plannets are there?

Paul Roche answered on 13 Jun 2010:

That’s a very good question, and one that we don’t yet have a good answer to. The reason Pluto was “dropped” from being a planet was that it started to become clear that it was not the only object of that sort of size on the edges of our Solar system, so as we started finding more and more of them the number of “planets” would start to get very large. There are now some dwarf planets, like Eris, which are even bigger than Pluto, so a decision was made to remove Pluto from the “normal planets”, and set up this new category of dwarf planets.

We think there are probably ~200 dwarf planets in the region we call the Kuiper Belt (a flat disc of icy/rocky material beyond Neptune), but maybe 2,000 or more dwarf planets if we consider the whole (roughly speherical) volume of space that is influenced by our Sun’s gravity (so including the vast Oort Cloud, where comets come from).

So the answer is probably that, eventually, we will discover hundreds or even thousands of objects like Pluto.