From the year 1930 up until 2006, you were always taught that there were nine planets in our solar system. Then, seemingly out of know where, scientists told us that in fact, there were only eight planets in our solar system and that Pluto was no longer considered a 'proper' planet but was now known as a dwarf planet. However, what exactly are dwarf planets and why are they not 'proper' planets?
What is a dwarf planet?
In simple terms, a dwarf planet is a body in the solar system which is massive enough to have its own gravitational pull but is not big enough to resist the gravitational pull of another object other than the sun. Although Pluto has a big enough gravitational pull to have its own satellite, Charon, its orbit is effected by the planet Neptune which causes it to orbit the sun elliptically as opposed to the circular orbit that the other planets have.
There are four other dwarf planets in our solar system which were previously considered to be asteroids and they are called, Ceres, Haumea, Makemake and Eris. Interestingly, Pluto is not even the biggest of the dwarf planets. Ceres is and is also the closest dwarf planet to Earth as it lies in the asteroid belt between Mars and Jupiter.
In fact, Pluto is not even the second biggest dwarf planet because Eris is ever so slightly larger. Eris lies along with Pluto and the other three dwarf planets in the Jupiter belt which orbits the Sun beyond Neptune, the eighth planet.