Ah Pluto, the world’s favorite planet-in-exile. Pluto was once a proud little planet orbiting at the farthest reaches of the solar system. Stuck in a highly eccentric orbit (that occasionally crosses neptune’s) Pluto was once an underdog of sorts, the little planet that could. But then in the year twenty-aught-six, Pluto was stripped of the only thing it had, it’s planet-hood. And my oh my has the reaction been fierce. How do I know this? Well it’s been close to a decade and we’re still talking about Pluto! On the plus side it also spawned the greatest pick up line in the history of man kind.
It turns out defining what is and is not a planet is kind of a tricky business. There’s a lot of junk in the solar system, like a lot of junk, so the question becomes where do you draw the line between different types of objects. It hardly seems fair to group massive planets like Earth in with tiny asteroids and space debris.
The easiest thing you could do is to just say, ok Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus, and Pluto are planets. But this isn’t elementary school, scientific definitions need to be rigorous, meaning the apply in any situation or circumstance. You could say, well it has to be a certain size. But what size? does it have to be at least 1 km across? 100km? What if something’s 99.9 km across, is it no longer a planet? No, that’s a bad way to go about it. How about shape. All the planets we’ve seen are pretty round. How about we say planets have to be round?
Alright that’s pretty good, it eliminates most space debris and other stuff we don’t care about. But wait what about the moon? Is the moon a planet? By that definition there would be upwards of 224 planets in the solar system. No, we need something more. We’ll add that they have to orbit the sun, they can’t orbit something else. So all the moons are out. That still leaves us with approximately (we have to guess because “dwarf planets” are small and hard to find) 60-ish bodies left. That’s a lot more than 9.
And this is where the controversy comes in. You see, back in 2006 scientists came to the realization that there are probably a lot of pluto-sized bodies in the solar system. Ones with dumb names like Haumea and Makemake (my apologies to the people that named those dwarf planets, but come on, you could’ve tried a little harder). And so suddenly the old times definition wasn’t working out. Hell could you imagine if you had to memorize 60 freaking planets in 2nd grade!
Now, most people would agree it doesn’t make sense to include the likes of bloody Haumea and Makemake on the list of planets, they’re tiny, poorly behaved, and don’t have the (pardon the phrase) star power of a planet like Jupiter or Mars. But Pluto is just like them, it’s small, smaller than the moon in fact, and it’s poorly behaved.
In fact, the more an more you look at Pluto, the less it looks like a planet and the more it just looks like a really big asteroid (it also spends a little too much time with those ruffians in the Kuiper Belt). Sadly, we can’t leave Pluto on the list just for the sake of nostalgia, and so the International Astronomical Union (aka the guys in charge of deciding what is and is not a planet) was forced to strike it from the official list of planets. They added one more qualification to planet-hood: You must have cleared the neighborhood of your orbit. Meaning you must be the most dominant thing in your orbit, you can’t cross paths with other large bodies, and you can’t be measurably affected by anyone else’s gravity (not including that of your moon(s)). Basically you have to be well-behaved. Sorry Pluto, that doesn’t include you.
But all is not lost, Pluto has a place in the solar system, we can’t just eject it from the records and pretend it doesn’t exist, we’re scientists, not monsters. And so we gave Pluto it’s own classification “Dwarf Planet”. Personally I am of the opinion that it is a more fitting definition. It doesn’t really fit in with with “big 8” but at the same time it’s hardly and asteroid, it has moons and an atmosphere, hell it could even have rings (although I wouldn’t count on it)! We can’t banish Pluto to the realm of “small solar system bodies” but we can certainly make it king of the Dwarven kingdom.