Sit down. Look at me. Are you looking? Okay, now listen closely. I know it hurts, I know it betrays the memory of your favorite third grade acrostic, and I know you don't want to hear it, but Pluto is not a planet. It never was. The mistake was calling it a planet in the first place.
It's nothing personal. It's not like we like Pluto any less for being a dwarf planet. Some of my best friends are dwarf planets! It's just that the evidence is all there in support of Pluto's demotion, and the only compelling argument to the contrary is basically just nostalgia.
|And what has nostalgia brought us?|
Pluto was discovered in 1930 by Clyde Tombaugh, a 23-year-old astronomer from Kansas. Given his youth, he was assigned the arduous task of taking pictures of the sky every two weeks and comparing the two to see if anything had moved. Shortly after he began his work, something moved, and that something was Pluto.
|Ladies love the 'scope|
Initially, astronomers thought that Pluto was around the size of Earth. Since that time, estimates have been repeatedly revised downwards. The most recent evidence puts the size at about .6% of Earth. That's "zero point six percent," not "six percent." It's really damn small, is what I'm getting at. It's small enough that its satellites have a sufficient gravitational pull to make Pluto sort of revolve around itself.
|Pluto...wat are you doing?|
Don't worry, though, I'm not just picking on the little guy. That's not the only reason Pluto was begging for the boot. After all, if I learned anything from Star Wars it's that size matters not. Orbit does, though, and Pluto's orbit...well...
|Go home, Pluto, you're drunk|
Yeah. Pluto's not really being a team player in that regard. It's orbit has more in common with a comet than a planet. In fact, it even weaves its way in and out of Neptune's orbit at different times. Planets don't get all up in one another's grill like that. That's Planetary Etiquette 101. You orbit like a planet and you own the neighborhood. Pluto does neither.
|KEEP YOUR HANDS TO YOURSELF, PLUTO.|
What really did Pluto in was the fact that we found other objects like it in the Kuiper Belt. The final nail in the coffin was the discovery of Eris. Until that point, the tentative agreement among astronomers was that as long as all those Kuiper Belt objects were smaller than Pluto, we'll keep telling ourselves that it's a planet. Then Eris came along, and it had more mass. By 27%, too, so it's not even close.
If that's not enough to sway you, let me ask you this: Are you upset that Ceres is not a planet? How about Pallas? Juno? Vesta? Are you willing to fight for their inclusion in the planet club? Because they were demoted, too. When they were first discovered, all four of them were considered planets. Then astronomers realized that they were all on the same orbit, and they shared it with a bunch of debris. So they were demoted, and we started calling them asteroids (although some asteroids have actually been promoted to dwarf planet status now).
|You can sort of see why we had to be a bit more specific with the "planet" title here.|
There are basically two ways of taking this information in. The first is to rage against the astronomers. You grew up thinking Pluto was a planet, so a planet it is and that's that. There's no better way to label that reaction than to call it anti-science. The point of any scientific pursuit is to be willing to challenge previous discoveries. To deny new discoveries because they conflict with your feelings is to deny critical thinking.
The other way to look at it (while still maintaining your love for old Pluto) is to realize that Pluto wasn't the last discovered planet, but the first acknowledged dwarf planet. Being the first, Pluto gets a whole range of benefits, not least of which is the fact that a whole class of dwarf planets are now named plutoids. This isn't the story of Harry Pluto being bullied and shunned by the muggle astronomers, this is Harry Pluto finding his Hogwarts.
|And yes, I did go there|
Don't cry for Pluto. Give it a pat on the back and a congratulations. While you're at it, keep your eyes peeled. Next summer, for the first time, we'll have actual pictures of Pluto. The New Horizons robotic spacecraft is scheduled to get there sometime in July.
Before you dismiss this whole thing as a silly and pointless argument, give it some real thought. How we categorize the universe will inform how well we understand it. If we get it wrong just because we're used to the wrong answer, we'll never understand the way the universe works, and it'll be our own fault. Denying the recategorization of Pluto is denying critical thinking. It's the same frame of mind that gets people to think vaccines cause autism, which leads to children dying of preventable diseases.
This stuff matters.