Photo: A high resolution, color-enhanced photo of Pluto taken by the New Horizons Spacecraft | NASA/JHUAPL/SwRI
Currently, the International Astronomical Union (IAU) officially classifies five celestial bodies in our solar system as dwarf planets: Pluto, Eris, Ceres, Makemake, and Haumea. Dwarf planets are defined as objects that orbit a star (such as our Sun), are roughly spherical in shape,1 and can sometimes have other large bodies such as comets, asteroids, or other dwarf planets orbiting near them. Astronomers have identified many other objects that could be considered for the category, and it’s estimated that hundreds or even thousands more could exist, scattered throughout our solar system.
1 A fancier term for this concept is “hydrostatic equilibrium”!
Formerly considered to be the ninth planet in our solar system, Pluto was downgraded to dwarf planet status in 2006—a controversial move decided in a vote by the IAU. Pluto meets all the criteria for a full-fledged planet but one: it isn’t large enough to have gravitational dominance over the celestial bodies around it; in other words, it doesn’t “clear its neighborhood” of objects like asteroids, comets, and other dwarf planets. Pluto is the largest known dwarf planet in our solar system. It ...