NOTA Cosmos: The Nineth Planet Controversy

In July 2005 the discovery of the dwarf planet Eris which was initially thought to be of the same size as Pluto (in fact it is 27% larger than Pluto) is often cited as one of the key arguments for the reclassifying of Pluto’s planetary status. The official story goes that a debate was held by the International Astronomical Union (IAU) leading to a resolution in which it was stated that in order for an object to considered a fully-fledged planet in our Solar System it must satisfy three criteria: 1) The object must orbit around the Sun; 2) 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; 3) It must have cleared the neighbourhood around its orbit.  Like Eris, Pluto only satisfies the first and second and fails the third, thus, the argument goes, is the reason for declassifying it as the nineth planet proper in our solar system and reclassifying it as a dwarf planet.

However, the reality is somewhat different. Senior experts at NASA told NOTA reporters in an exclusive interview that the reason that Pluto cannot be the nineth planet in our solar system is that there is only one Number 9 . . . Go here