Pluto is a dwarf planet (or plutoid) that usually orbits past
the orbit of Neptune. It was classified as a dwarf planet in 2006;
before that it was considered to be a planet, the smallest planet
in our solar system. There are many other dwarf planets in our
Solar System. Pluto is smaller than a lot of the other planets'
moons, including our moon. Pluto has not been visited by spacecraft
yet; we only have blurry pictures of its surface; even the Hubble
Space Telescope orbiting the Earth can only get grainy photos
because Pluto is so far from us. In 2015, a spacecraft called
New Horizons (launched by NASA in 2006) will visit Pluto.