13 Responses. There are 12 planets in the solar systemâMercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, MakeMake, and Eris. Itâs not the International Astronomical Union but four percent of that group that voted on excluding Pluto in a sloppy, nonsensical definition that states a dwarf planet is not a planet at all.