The distant cue ball of a frozen world known as Pluto has always been a space oddity (it’s smaller than Earth’s moon and follows a squashed orbit around the sun that takes 248 years). When astronomers began discovering other heavenly bodies rivaling tiny Pluto in size, they started to rethink their definition of a planet. Pluto no longer made the cut.
Pluto was originally classified as a planet, but is now known as a “dwarf planet”. In 2005, an American astronomer called Mike Brown thought that he had found a planet further out in the solar system than Pluto. This new planet was thought to be the tenth planet in the solar system, and was named Eris.
However, this prompted the International Astronomical Union (IAU) to decide that “planet” actually needed to be defined, to see if Eris would fit into the definition. So, in 2006 the IAU decided that to be a planet, the object must:
- Orbit around the sun
- Be massive enough to be pulled into a the shape of a sphere by its own gravitational force; and
- Have ‘cleared the neighbourhood’ around its orbit. This means there must be no other bodies in its orbit that are not under its influence (like a moon).
Picture Credit : Google
