Poseidon, the 10th planet?

You have to understand that as telescopic and computing power increase, we will be finding tons of new "planets" in the solar system. Most people agree, that Neptune is the last "true" planet in the solar system. Pluto is likely just an object in the Kuiper Belt, an area on the outskirts of the Solar System, where the Sun's influence dwindles rapidly and there are tons of rocks floating around. Pluto has a minor atmosphere and a moon, Charon. There is a debate that starts up every time a new large object is found around where Pluto is, this happens every few years. Bottom line: there probably won't be any more planets added to the roster, and Pluto won't lose its planetary status...there is just too much involved in changing things. So, to answer your question, Poseidon probably exists, but its probably not going to be a planet.

Tenth Planet Solar System

there will be only 10 planets .. and poseidon

Mini Pluto is 10th. Poseidon is the 11th :)

You see, I had never heard of ten planets. I only heard 9 planets; Mercury to Uranus to Pluto.

well, I know if Sedna and Poseidon and something else, but I think they were too far in the Kuiper belt and were, in the end, classified as asteroids.