What’s in a name? That which we call a rose
By any other name would smell as sweet. -W. Shakespeare
After writing about the 80th Birthday of Pluto becoming a planet, I was asked about Pluto’s planetary status, and whether I thought it deserves to be a planet or not. Let me just recap for you, very briefly, what this argument is all about.
Pluto, when it was discovered back in 1930, was the only object in the Solar System found out beyond Neptune. Although we imaged it, observed it, and surveyed the whole sky for other objects, it remained the only Solar System object out beyond Neptune until the 1970s, when Pluto’s giant moon, Charon, was discovered.
But this all changed severely in the 1990s. A whole zoo of “trans-Neptunian” objects were discovered, many of them of comparable mass and size to Pluto. In 2003, Eris was discovered, and this was big news to people who were worried about what counts as a planet and what doesn’t. Why? Because Eris was larger than Pluto!
So, the argument went, if Pluto was a planet, then Eris needed to be one also. If Eris wasn’t a planet, then Pluto couldn’t be one either. So what do we do? For nearly three generations, we all learned that there were nine planets in the Solar System; was it necessary to change all of that?
Putting aside what the IAU decided — which was to demote Pluto to “dwarf planet” and promote Eris and others to “dwarf planet” — let’s think about it. What’s really going on in our Solar System?
Close to the Sun, we’ve got four rocky planets — two with moons — and nothing else. If there’s anything interesting going on from the Sun out to about 300,000,000 km away, it’s probably happening on Mercury, Venus, Earth, Earth’s Moon, Mars, or (possibly) Mars’ moons Phobos and Deimos. So it makes sense to have four inner planets. Beyond that?
But the Solar System is much more than just these four inner planets and the four outer planets, isn’t it?
In between Mars and Jupiter, we’ve got thousand upon thousands of asteroids, moving too quickly and of too low a mass to merge into a giant planet, much the same way Saturn’s rings won’t merge into a giant Moon. The largest of these asteroids is almost 1000 km across, and massive enough to have pulled itself into a sphere! Say hello to Ceres, as seen by Hubble.
Out beyond Neptune, there’s Pluto, Eris, Makemake, Haumea, and many other large bodies in the Kuiper belt, in addition to a bunch of smaller frozen rocks, some of which will one day become moons of the gas giants or comets!
Does the fact that Pluto lives in the Kuiper belt make it less special than if it were the only one out there? Does the fact that Ceres isn’t a standalone object, but has a whole host of neighbors make it less special than if it were on its own? Does Saturn’s moon Titan — with an atmosphere thicker than Earth’s — become any less special in your eyes because it wasn’t able to eat up Saturn’s rings with its own gravity?
The answer to all of these questions, of course, is no. These objects are special based on their own merits, not because of what’s going on around them. And if you don’t like the fact that the IAU called Pluto a “dwarf planet,” just call it “the planet Pluto.” The purpose of language is to communicate, and to be understood. I don’t adhere to MLA writing rules when they don’t suit me, and I think it’s the height of foolishness to expect that people will stop calling Pluto a planet (or stop thinking of it as a planet) when they refer to it.
So a recap of my thoughts? Call it whatever you want. It’s a fascinating member of our Solar System, the first trans-Neptunian object ever discovered, the pioneer in our understanding of the Kuiper Belt, and it remains an ignition switch to some of the best parts of our imaginations. If you want to say “dwarf planet Pluto,” we can still have a good chat about it, and the same goes if you say “the ninth planet,” “the former planet,” or just “Pluto.” It doesn’t change what it is, or how much we all care about it, and that fact is more powerful than any IAU ruling will ever be. Pluto has better things to do than care about whether you call it a planet or not.
So call it whatever you want; if I were Pluto, I’d be too busy orbiting the Sun.