Sucks to be Pluto

The moment I finished the space odyssey, I began getting grief about not including Pluto. Sorry friends, but Pluto is not a planet. Sure it used to be, but it was downgraded. Like most other scientists I have to agree that it doesn’t deserve to be in the same class as bodies like Jupiter and Saturn.

The International Astronomical Union (IAU) is who started the drama around Pluto. They are the big shot organization that controls how we think about space. They are also the ones with the authority to name heavenly objects.

The drama started in January 2005 when Eris (official name: Eris 136199) was discovered. Eris was found orbiting out past Pluto in the Kuiper Belt. It was determined to be 27% more massive than Pluto. NASA started calling Eris the tenth planet and got excited about the high probability of finding more planets, but the IAU had something to say about that.

In August 2006, the IAU held a meeting in Prague and passed Resolution 5A. This resolution established guidelines to determine if something is a planet or a dwarf planet.

To be a planet, an object must:
1. Orbit the sun
2. Be large enough to produce enough gravity to make itself (mostly) round
3. Clear the neighborhood around its orbit

To be a dwarf planet, an object must:
1. Orbit the sun
2. Be large enough to produce enough gravity to make itself (mostly) round
3. Not have cleared the neighborhood of its orbit
4. Not be a satellite (moon)

All other objects (i.e. comets, asteroids, etc) are classified collectively as “Small Solar System Bodies”.

Pluto is tiny (only about 70% the size of our moon), but it is able to meet requirements one and two of being a planet. The problem lies in requirement three. Pluto orbits in the Kuiper Belt (basically the same thing as the asteroid belt, just a little larger. It starts right outside the orbit of Neptune). A true planet would have cleared the belt out of its orbit, but Pluto did not.

Picture from http://www.mathiaspedersen.com/

Just like that, Pluto got its planet card revoked. Our solar system only contains 8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune). In Resolution 6A, Pluto was officially named a dwarf planet as well as the prototype for a new variety of trans-Neptunian objects, which (according to Resolution 6B) will be called “Plutonian Objects”.

Now Pluto gets to hang out with the other dwarfs, like Ceres and Eris.

Whatever, I would rather hang out with them anyway!