Small planet is a term used to describe celestial bodies that are much smaller than the planets in our solar system. PLUTO, an example of a small planet, is a dwarf planet with a diameter of 2, 390 km and is the second-most-massive known dwarf planet in the Solar System. ASTEROID is another example of a small planet, which is a rocky body orbiting the Sun. CERES is the largest ASTEROID in the Solar System, measuring 950 km in diameter.