One for the star-gazers on this day, as American astronomer Clyde Tombaugh, discovered the ‘ninth planet’, Pluto exactly 84 years ago.
Not to take anything away from Tombaugh’s incredible discovery, but Pluto has been officially downgraded since then and is now regarded a ‘dwarf planet’, confusing school children across the globe who now can’t make head nor tail of how many planets there are in our solar system. (Answer: eight)
Officially reclassified in 2006, Pluto’s status created controversy amongst the International Astronomical Union, who eventually agreed on the following set of guidelines to fully define an actual planet:
- The object must be in orbit around the Sun.
- The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
- It must have cleared the neighbourhood around its orbit.