Dwarf Planets

A dwarf planet is a celestial body which is too small to be considered a real planet but too large to be called a space rock. It must revolve around the sun and it should not be a satellite of another planet. Hence this disqualifies earth’s big moon from being a dwarf planet.

Our solar system currently has three dwarf planets. These are Ceres, Pluto, and Eris. Ceres was the first dwarf planet discovered and at first was classified as a large asteroid. However this was later corrected after discovering that it had not only its own inner core, but a very thin atmosphere and gravity.

The second dwarf planet Pluto was first considered a small planet in itself but its orbit crosses the Kuiper Belt in the same way that Ceres moves among asteroids within the asteroid belt making Pluto a dwarf planet. 

The last dwarf planet is Eris which is also the largest and coldest dwarf planet and was discovered in 2005 beyond the orbit of Pluto.