Pluto is the ninth and usually the farthest planet from the sun in our solar system. It is also the smallest planet in our solar system and the last to be discovered. It is smaller than a lot of the other planets' moons, including our moon. Pluto is the only planet in our solar system that has not been visited by our 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.