It also the smallest planet in our solar system and the last to be discovered. Pluto Pluto, which is smaller than our moon, is a cold, dark, frozen place. We don't know very much about the tiny planet.
Scientists think it is made of rock and ice.
It might have a thin atmosphere of nitrogen, carbon monoxide and methane. Pluto Pluto is the ninth, or last, planet in the solar system. The orbit, or path the planet takes around our Sun is an ellipse, or stretched out circle. For this reason there are times when Pluto is the furthest away from the Sun. There are also times when it is closer to the Sun than Neptune.