Neptune is the outermost planet in our Solar System. It used to be Pluto, but Pluto was disqualified from planetary status a few years ago. Sorry, Pluto, but that's just the way it is. The reasons for doing so, however, are exciting - there could be many planet sized objects beyond Neptune, and some of them could be the size of Earth!
The Oort Cloud - named after Dutch astronomer Jan Oort - is thought to be a giant shell of icy elements - comets, rocks and other galactic debris - that encircles the entire solar system. Oort believed that it contains material cast out from the formation of our solar system and is the probable origin of most of the comets that pass by Earth, for example Haley's comet. Many of the bodies within the Cloud could be Earth sized - or at least dwarf planets - and we call these 'plutoids' in honor of Pluto.