These discoveries compelled us to rethink our definition of a planet, culminating in the official 2006 definition of "planet" by the International Astronomical Union (IAU). Lowell Observatory ArchivesWhen we first discovered Pluto, it was crazy to think it was anything other than a planet. These exoplanet solar systems have proved to be vast, varied and rich, showing us that our Solar System is both nothing special and not even necessarily the norm. In fact, over 100 known objects in our Solar System alone would become planets. There's something very meaningful about our place in the Solar System that makes Earth a planet and Pluto not-a-planet.

Source: Forbes March 08, 2017 15:00 UTC