Planet Pluto

Pluto absolutely is a planet. Only four percent of the International Astronomical Union took part in the controversial decision to demote Pluto, and most of them are not planetary scientists but other types of astronomers. Their decision was immediately rejected by an equal number of professional astronomers in a petition led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto and one of the leading Pluto experts in the world. The IAU definition that excludes Pluto from being a planet makes no sense in that it states that dwarf planets are not planets at all, and also in that it defines objects solely by where they are rather than by what they are. According to the IAU definition, if Earth were in Pluto’s orbit, it would not be considered a planet either. This could easily be corrected with an amendment stating that dwarf planets (the category in which they placed Pluto, really just a term for small planets) are a subcategory of the broader term planet. Many astronomers believe that the term planet should be kept broad to encompass any non-self-luminous spheroidal object orbiting a star. In other words, if it’s round and orbits a star, it’s a planet. That is because round objects are in a state of hydrostatic equilibrium, meaning they have enough self gravity to pull themselves into a round shape. When this happens, these objects become differentiated with core, mantle, and crust, just like Earth, and develop geological processes akin to those on the other major planets–processes that do not take place on inert, shapeless asteroids. So by this broad definition, Pluto most certainly is a planet, as are Ceres, Haumea, Makemake, and Eris–giving our solar system a current total of 13 planets.