Celestial bodies are recognized as planets, based on several criteria. The scientists demoted Pluto to a dwarf planet in 2006 when the definition of a planet changed. Since then, there are only 8 planets in our solar system.
Recently, a group of scientists have proposed a new way to classify planets. This will possibly add about 100 objects into the “planets” list.
While in 2006, when the International Astronomical Union changed the definition of planet and removed Pluto from the planet list. It’s demotion is attributed to discoveries that show it is actually a Kuiper Belt Object.
The scientists, then in 1930, did not know much about the Kuiper Belt objects. When they discovered Pluto, they included it as the ninth planet of the Solar System. But, later on, they discovered several such bodies which were bigger than Pluto in that belt. This demoted Pluto. However, the discovery of Eris, a dwarf planet 27 percent larger than Pluto led IAU to come up with a formal definition of a planet.
According to IAU, “A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit,” is termed as a planet.
Now, scientists propose a new definition for the planets. Kirby Runyon of Johns Hopkins University and the team proposed this new view. According to them the factors that need to define a celestial object as a planet should rely on the body itself and not just other factors. Runyon said that no planet has actually totally cleared its orbit. They defined a planet as “a sub-stellar mass body that has never undergone nuclear fusion”.
Based on the team’s definition, Jupiter’s moon Europa and even the Earth’s moon would be classified as a planet. If IAU adopts this definition officially, then we will have 110 planets. This is a lot to read and remember for the future generation.