Happy Fourth of July! The title of this blog post is from the book written by Mike Brown, “How I Killed Pluto and Why It Had It Coming”. Mike Brown is the discoverer of Eris, the Kuiper Belt Object (KBO) that is/was larger than Pluto* and sealed Pluto’s fate; in fact, he goes by his Twitter handle @plutokiller.
Pluto is not a planet. There, I said it. And I stand by it. Yeah, I’m gonna go there, and I do expect plenty of hate from this, so let it fly! Please note that although I consider this to be a good collection and presentation of the arguments against Pluto, ultimately, who really cares? It’s not as if I’m so invested in this that I would spend the last few days typing this up, checking my sources, proofreading it, and making sure everything is correct, y’know. Ahem. Please take this post in the playful spirit in which it is intended, and when you crucify me, please do so lovingly. Also, please note that there is a little salty language below, a first for this blog, but it’s in the aid of comedically making a point.
Did you know that for the first half of the Eighteenth Century there were ELEVEN planets? Yup, you read that correctly – eleven. There were the six traditional planets – Mercury, Venus, Earth, Mars, Jupiter, and Saturn. William Herschel discovered Uranus in 1781, so that makes 7. (Me, I probably discovered mine as a baby, but I digress.)
In 1801, Giuseppe Piazzi discovered the 8th; and within a few years, Heinrich Olbers discovered the 9th (1802), Karl Harding discovered the 10th (1804), and then Olbers discovered the 11th (1807). These bodies orbited between Mars and Jupiter and were named Ceres, Pallas, Juno, and Vesta, respectively. And for over 40 years, they were considered to be planets.
However, starting in the mid- to late-1840s, more of these objects were discovered. By 1850 there were 10 of them in total, and by 1860, there were 57. The original four objects were DEMOTED from being planets and are now simply referred to as being asteroids. They reside in the asteroid belt with literally hundreds of thousands of other such bodies.
If any of this sounds familiar, it’s because this is EXACTLY what happened with Pluto.
At first, when Pluto was discovered, based upon its actual brightness and what astronomers believed to be the most likely darker color of its surface, Pluto was estimated to be the size of the earth. Then, as observations and measuring techniques got better and better, that size estimate fell to being the size of Mars, then Mercury, then our Moon.
This is because, as New Horizons recently discovered only a couple of years ago, a lot of Pluto’s surface is made up of frozen water ice and nitrogen ice. Pluto has a very high albedo – the percentage of sunlight that reflects off of its surface. Earth’s albedo is pretty high at 30% – we’ve got lots of oceans reflecting lots of light. Think of how bright things are when you go to the beach. But Pluto’s albedo is much higher, estimated to be at about 50-60%. As bright as things are at the beach, think of how much brighter things are when there’s snowfall everywhere. Because astronomers thought that Pluto would be much darker than it actually is, the fact that it was brighter than expected led them to believe that it was much larger.
In fact, it turns out that Pluto is even smaller than our own moon. If you placed Pluto on top of Australia, you’d still be able to easily see Perth and the entire west coast on one side and Melbourne and the entire east coast on the other. It doesn’t come anywhere near close to covering Australia, earth’s smallest continent. That’s how small Pluto is.
Starting in the 1990s, and led primarily by the aforementioned Mike Brown, hundreds of other bodies were discovered orbiting the sun way out Pluto’s way, in an area of the solar system that was called the Kuiper Belt. To those that argue that we don’t make a designation of something because of where it is, rather than what it is, they are dead wrong. Ceres, Pallas, Juno, and Vesta are living proof and would demand justice if the reverse were true.
Just like the asteroids, and in fact, EXACTLY like the asteroids, Pluto is one of many objects within a vast belt of them. The asteroids are in the asteroid belt; Pluto is in the Kuiper Belt. Pluto gets downgraded from being a planet, and that’s that.
As Neil deGrasse Tyson argues, Pluto is not like other bodies in the solar system in a lot of ways. Where planets orbit the sun in a tightly defined plane called the Ecliptic, Pluto does not. It orbits at a 17-degree tilt to the Ecliptic.
Where planets orbit the sun in their own orbits, Pluto does not. Pluto’s orbit crosses the orbit of Neptune. That’s embarrassing for something that’s supposed to be a planet. You know what types of objects cross the orbits of planets? Comets.
And lo and behold, if you brought Pluto in closer to the sun, it would melt and grow a nice long tail, just like a comet. And that’s embarrassing for something that’s supposed to be a planet, too.
Pluto’s mass is only one-fifth of our moon’s. That’s pretty embarrassing, too. And I’ll add to Tyson’s arguments that Pluto is tidally locked to its moon. That’s no behavior for a planet to have. Moons should be tidally locked to their planets, not the other way around.
All Pluto’s got going for it is a dopey Disney character, a vomit-inducingly overly cute heart (yes, of course, I’m kidding), and just a bit more seniority on the “I used to be a planet” roster – 70 years versus 45 – over Ceres, Pallas, Juno, and Vesta. But where are the crowds demanding those others to be restored, hmmm? Where are the marches on Washington for the “Former Four”? Where are the politicians out campaigning on that issue? #NoOneWeepsForCeres
If it could happen to Ceres, it should happen to Pluto. Pluto had it coming, all right.
Now, if you still believe that Pluto is a planet, well, science doesn’t care what you believe. Wait! I’m not trying to be a jerk (although I might be succeeding regardless).
Science is about categorizing things so that you can learn something from that categorization. Think about biology for a second – all of life is categorized into kingdom, phylum, class, order, family, genus, and species. And those classifications mean something; the various classifications tell you something specific about the life form or the group of life forms – invertebrates, plants, hominids – that you are discussing. Each of those things share very specific characteristics with others within their own group that no other thing shares.
The word planet did not even have any formal scientific definition until Mike Brown discovered Eris in 2005, a KBO larger than Pluto.* Until that point, planet was merely the Greek word for these “wanderers” in the sky, moving amongst the stars. Before Brown discovered Eris, other KBOs had been discovered, but they were all smaller than Pluto. Eris being larger, pressed the issue – are Eris, Haumea, Makemake, Sedna, Quaoar, and other KBOs planets too? Something had to be done. Either all of these objects (and Ceres, too) were planets, or none of them were – including Pluto.
The International Astronomical Union met in 2006 to decide the issue. It formed a committee to develop a definition of planet. One definition would have resulted in 12 planets, including Pluto, Charon, Eris, and Ceres. The astronomers present voted that definition down. Instead, they voted in this definition:
A planet is a celestial body which:
1) is in orbit around the Sun, [as opposed to just “a star”, so it doesn’t apply to exoplanets]
2) has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3) has “cleared the neighborhood” around its orbit.+
This classification of Pluto as no longer being a planet, but instead being a KBO, tells us something new about Pluto, something we didn’t know, and wouldn’t know, by continuing to call it a planet – that it hasn’t cleared its orbit of other objects. This new classification adds to science by adding to our understanding of the object.
Moreover, saying that a dwarf planet is still a planet because a dwarf person is still a person shows that you are being swayed by emotion, and not by logic. We’re not discussing politics and civil rights; we’re talking about science. Just because something is politically correct doesn’t mean that it carries over and makes it scientifically correct as well. A dwarf planet is in an entirely different category than a planet that just happens to share a word in common.
Are exoplanets planets, too? We don’t know. We can’t collect enough data from our distance from them to be able to determine if they meet the IAU three-part definition. Sure, they meet the first part, directly orbiting their sun. But are they round? Are there other bodies of similar size orbiting with them?+ We don’t and can’t possibly know. This is why the definition was limited to our own sun, our solar system.
Interestingly, why was Charon – Pluto’s moon! – included on the original new list of 12 planets? At 753 miles across, Charon is over half the diameter of Pluto. Charon was thought to be a planet because not only does Pluto not qualify as a planet under the third part of the definition – clearing its neighborhood – but it also doesn’t qualify under the first part of the definition, either. Pluto does NOT orbit the sun. Yes, you read that correctly. Take a look:
Keep your eyes on Pluto. As you can clearly see, the two of them orbit each other, and more particularly, a point in space in between the two of them. And it is that point in space that orbits the sun – NOT Pluto. The original IAU definition would have Pluto and Charon as a double planet system. Pluto fails the definition not once, but twice.
Let me end this rant by discussing the process of Pluto’s demotion. Some <cough>Alan Stern<cough> complain bitterly about this process. This is only so much more whining, the very kind of whining that Ceres just pooh-poohed in its wonderful meme, above. Pluto was demoted by the IAU, the governing body, in a fair vote, announced in advance. Pluto lost fair and square.
To those that say “the people who had more of an interest in voting on the subject of Pluto had already left the meeting, or couldn’t attend in the first place,” tough. That’s like saying – that’s EXACTLY like saying – that those who didn’t vote in the Presidential election would have changed its outcome. Yeah, so? As we used to like to say back in New York, that and three bucks will get you a ride on the subway.
The fact that the outcome may have or even would have been different had these people voted – in either election – is utterly MEANINGLESS. They knew the election was happening. If it were so important to them, they could have attended, they could have voted. Their complaints now are exactly the same as those people who didn’t vote in the 2016 election and complain now: You don’t vote; you don’t have a right to complain. Again, the answer is tough. Period.
Finally, the real clincher in all of this is that the vote on Pluto’s planetary status was held way back in 2006. The IAU meets every three years. Since the demotion, the IAU has met in 2009, 2012, and 2015. If there really are more votes “out there” to return Pluto to planethood, then where were these voters for the past three meetings? Why haven’t they come out, en masse, with righteous indignation and overturned this obvious injustice?
The answer, as Jerry Seinfeld’s father Morty said about his impending impeachment as condo board president, is because they don’t have the votes. If they did, Pluto would already have been returned to planetary status years ago, in yet another fair election. It hasn’t; and that means that people who “believe” that Pluto is a planet are just dead wrong.
More important than this entire rant is the fact that everyone who is anyone in astronomy and planetary science says, none of this – none of any of this – makes Pluto any less worthy of an object for study. It is interesting; it is fascinating, Spock. I want a New Horizons 2 and 3 and 4. I want orbiters and landers – and not just on Pluto, but all over the solar system.
But a planet? Nope. Not a chance. Instead, why not call anything out there that’s round a world? World is inoffensive to everyone. Titan, Europa, Enceladus – these are just a few of the fascinating places, the worlds out there that await our further exploration. As is Pluto.
So, I’ve probably just offended about half my readers. If so, comment! Argue for your side! Tell me – why is Pluto a planet?
* Further refinements in observations and measurements show that Pluto is probably a smidge larger than Eris.
+ Note the terminology “‘cleared the neighborhood” around its orbit”. Some people <cough>Alan Stern<cough> have argued that many of the eight planets in our solar system do not meet this requirement. The earth, Jupiter, Saturn, and other planets have groups of asteroids that orbit 60 degrees ahead and behind them – right in their orbits – at the Lagrangian points. I would think that a slight tweak of this portion to the definition to “cleared the neighborhood of bodies of similar size around its orbit” would be sufficient to shut this guy, er, these people, up.