In 2006 the International Astronomical Union decided what makes a planet an actual planet. This definition bumped Pluto down to the ranks of dwarf planets. Not everyone was pleased with this. People petitioned to have the decision reversed. The state of New Mexico actually voted on the issue. For what it’s worth, Pluto is still a planet whenever it passes over the state of New Mexico. But why is Pluto a dwarf planet and not an actual planet?

Pluto, compared to our Moon, is really not very big

It’s really, really, f&%king tiny!

Okay, that is not entirely fair. Size actually doesn’t matter that much when it comes to planets. There are a few rules that a planet needs to follow to be considered a planet:

  1. It has to be spherical. (or really, really close to spherical)
  2. It has to orbit the Sun
  3. It has to have cleared the neighborhood around its orbit

Pluto is spherical and it orbits the sun, the problem is that it is surrounded by other objects. Now, a planet can have some objects around its orbit (Earth has the moon, for instance), but Pluto’s total mass is only 0.07 times the mass of the stuff around it. When it absorbed all those objects, or knocked them out of the way, Pluto will be a planet again.