you wondering how many planets are in the Solar System? Until just a few years ago, there were 9 planets in the Solar System. However, the International Astronomical Union decided that Pluto is no longer a planet, so there are now only 8 planets in the Solar system. Why is Pluto not a planet? We have a whole article that discusses this in great detail, but it happened because astronomers discovered a new object larger than Pluto out beyond its orbit. This object is called Eris, and it’s at least a few hundred kilometers bigger than Pluto. The IAU wondered if this object should be considered a planet too?