1. And then there were eight
At school, most of us were taught there were nine planets in our solar system. But something changed and now there's only eight. When Nasa’s New Horizons mission was launched at the start of 2006, Pluto was a planet, but it's not any more.
Pluto is only 1,430 miles (2,302km) in diameter and that makes it smaller than our Moon. Pluto is 3.7 billion miles (5.9 billion km) from the Sun – that’s 40 times the distance the Earth is from it. Consequently, it was the last 'planet' discovered. It took until 1930, because it was so small and too far away to be seen without the aid of a powerful telescope.
It ended up being a case of ‘last in, first out’ as Pluto was kicked out of the planet club in 2006.
2. What makes a planet a planet?
In 2006, the International Astronomical Union put forward a new definition for what makes a planet. Which of these criteria did Pluto fail?
3. Bye, bye Pluto
Because Pluto does not have enough ‘gravitational influence’ to clear its neighbouring orbit it was decided it did not make the cut.
Instead it was rebranded as a ‘dwarf planet’.
Dwarf planets are not officially full-fledged planets, so Pluto was stripped of the status it had held since its discovery in 1930.