Pluto in the Solar System Toy Box

Since I run a campus observatory, I'm often asked about what I think about Pluto getting "demoted." First, Pluto wasn't demoted, it was reclassified. Unfortunately, the astronomers/IAU aren't exactly clear yet on the classifications -- I'm personally leaning towards the Star Trek classifications myself.

Here's how I explain it:

When you are young and you only have a few toys -- a crayon, a doll, a puzzle -- it makes sense to put them all in one toy box. But as you have more birthdays, you get more toys. Now you have lots and lots of crayons and coloring books, lots of toy cars, lots of Legos. Now it makes sense to have a container for each kind of toy. All of the crayons and coloring books could go in one box while the Legos would go in another. It wouldn't make sense to mix them all up.

And that's how it works in astronomy. For a long time, we only knew about the 'planets' and that included Pluto. But then we started learning more and more about the outer Solar System and we recognized that Pluto doesn't quite belong in the same box as the other planets.

And it's not like this is the first time this has happened! Back in the 1800's when the asteroids (at least that's what we call them now!) were first being discovered, they were also classified as planets. But after about 50 years (and several dozens of asteroids), the astronomers finally agreed that the objects they were discovering weren't like the other planets and because of their star-like appearance, called them asteroids (aster is the Greek word for star).

And as we learn more about own Solar System and observe planets in other solar systems, we will eventually find a classification scheme that works. We should be excited that we have new boxes to use as we sort through the objects in our Solar System!