For a not-so-recent birthday, I got given a lovely T-shirt with very cutesy renditions of all the planets on it; with each one sporting a friendly face and a colourful label. It’s the perfect blend of astronomer & dad nerd. But one thing about it that I almost totally missed when I first saw it, was the sneaky inclusion of Pluto, hanging out with the rest of the gang; partying like it’s 1999.
The shirt is a recent design —newer than 18 years, at the very least— and I would argue Pluto’s planetary declassification is probably one of more better-known bits of astronomy trivia in the mainstream. So really, whoever had included it had to be aware of Pluto’s non-planetary status and did it deliberately. The question is, why?
It turns out that quite a lot of people are remarkably loyal to this ball of ice and rock 1/6th the mass of the moon, hanging out on average about 40 times further from the sun than we are. How loyal, you say? Well, aside from a (admittedly not completely serious) pledge by the state of California that Pluto will always be treated as a planet, there seems to be a general, grassroots sentiment that Pluto was short-changed by a stuffy scientific establishment, out-of-touch with the people. “Make your mind up, scientists!” & “I was taught there was a planet there, so that’s what I’m going to keep believing.” And so on.
For what it’s worth, I don’t think the fanaticism is about the rock. This phenomenon seems to have a whole lot more to do with distrust of science, anti-authority, conspiracy theory and generational solidarity.
Leave Pluto Alone!
So, why do we gotta be mean to poor little pluto? Can’t it just be a planet?
Allow me to tell you the sad tale of a celestial body robbed of it’s planethood, due to the fickle nature of scientists. At the turn of the nineteenth century, Giuseppe Piazzi —an Italian priest— was observing the sky searching for a particular star, when he noticed an object that appeared to be a comet. After some repeated observations, it became clear that what Piazzi had in fact found was none other than a brand new planet; to be added to the great pantheon that is our solar system. Its glory was not to last. Long after Piazzi was dead (and despite millions growing up being taught it was a planet), it was callously declassified and demoted by the scientific community.
That planet was, of course, Ceres.
Yeah, truth is, this isn’t the first time this has happened. Pluto got special treatment for a long time—and eventually, the scientific community realised it was going to have to be more specific in regards to what it meant by “planet”; or face a total mess of how many planets there are and which order they come in.
Colloquially, it’s pretty obvious what a planet is, right? It’s big, it goes around the sun, and you can walk around it without falling off (unless you’re a Flat-Earther; but that being the case, you ought to try anyway… if you’re right, everybody wins). However, science needs to be a bit more precise than that. It’s just one of those annoying side-effects that comes with attempting to know things that are actually true. What a drag.
For Success, You’ve Got to Planet
Okay, so, what technically makes a planet? In 2006, it was summarised as the following:
- Orbits a star? Pluto: “Check”
- Has enough gravity to condense into (some approximation of) a sphere? Pluto: “Check”
- Clears its orbit of other bits? Pluto: “…ah, balls”
I guess the obvious layman’s objection is probably: “Who cares about the last one?” But, it turns out, there’s quite a lot of rabble that would be let into the Planets list were we to grant Pluto a Greencard. We’ve already mentioned Ceres. And yes, while Ceres is smaller, Pluto is not the most massive of its dwarf planet brethren. That honour in fact falls to another out-there trans-Neptunian object: Eris. Not to mention others like Makemake, Gongong, Sedna and Haumea.
Glory to the Dwarves
So; Pluto is not the first, nor is it the heaviest of these would-be planets. But maybe, dear Plutocrats, you’re looking at this all wrong. Instead of trying to shoehorn a dwarf into the planetary category; perhaps we should focus on greater understanding of the category it actually fits in. In other words, Pluto, there’s nothing wrong with being a dwarf planet! Run with it. Wear it with pride.
And to all those who think that Pluto’s reclassification was somehow unjust or misguided, please take a look at the other dwarf planets out there. It’s really not bad company. It doesn’t change what Pluto is, or detract from its discovery, or even its historical place as once being considered a planet.
So I’m happy, actually, that the T-shirt included Pluto. Because it gives a chance to raise the subject and discuss terminology in astronomy and elsewhere. It’s a thing that’s always changing and improving; like science itself, always adjusting to better fit the facts. And things like ‘planets’ might seem like a fixture of the cosmic order of things; but they’re really just concepts that we (mostly) agree on.