Pluto

Pluto used to be the ninth planet — until scientists decided in 2006 that it was too small and reclassified it as a 'dwarf planet'. It's even smaller than our Moon! Pluto is incredibly far away: a spacecraft needs over 9 years to reach it. It's so cold there (−229 °C) that nitrogen freezes into ice and forms vast plains. Pluto has five moons of its own — the biggest is called Charon, and it's almost half the size of Pluto itself.