Be it a planet or dwarf planet, Pluto is the last of the original nine planets to be visited by a spacecraft. Its exploration will provide insight into a world far from the Sun and give us an idea of the characteristics of other similar worlds that we know of. There are currently four other known dwarf planets similar to Pluto and there may be as many as a 100 or more beyond the orbit of Neptune in a region of the solar system known as the Kuiper Belt.
As a side note, the other, or fifth, known dwarf planet, Ceres, currently has its own mission of discovery ongoing via the Dawn spacecraft. The Twitterers has been captivated by the mystery of the enigmatic “bright spots.” Their riddle will probably be solved when Dawn gets closer to Ceres.