The 6yo brought home a worksheet they did at school today about the planets of the Solar system. Each entry has a little line work picture of the planet printed that they colored and then a couple of sentences about the planet in which they wrote the name of the planet.
But I noticed there were 9 entries. Pluto's entry had a big 🚫 on it. Like not added after the fact by the teacher or anything. Just as part of the worksheet. 😆 Take that, Pluto!
@benhamill He also had good points about the internal dynamics of the bodies in question. Their geological processes are going to be quite similar to each other... and different from comets, asteroids, and other bodies that aren't triaxial ellipsoids.
It's a theoretical tug-of-war that's been going on for nearly 220 years, almost since Ceres was discovered in 1801.
@Qwyrdo These are delightful facts!
Under that hundreds of planets model, learning all the planets would be a bit like learning all the mountains: Each individual mountain doesn't even have a name to learn.
@Qwyrdo But, like, people still know what a mountain is.
@benhamill Exactly!
(IIRC this scientist was a relatively recent guest on Planetary Radio, planetary.org, so with just a little digging you can listen to the talk itself if you're interested :3)
@Qwyrdo Upon further thought, it might be interesting to have a separate technical definition for this person's idea. Like "world" or something. What I like about that is that it lets in there idea that some moons of gas giants might be more like Earth than the gas giant is in many ways, but different in others (like orbiting a star or a planet).
@benhamill It's kind of interesting how polarised the astronomical community is about the definition of planet. Guests on Planetary Radio give it a lot of shade.
There's also an astrogeologist (I forget his name) who, at an upcoming IAU conference, who's proposing a new (alternative) definition that would classify about 112 known solar system bodies as planets.
"But that's too many! How will kids learn all of them?"
His answer: they don't need to. Give them the definition & let them infer what is, and isn't a planet.
He likened this to the periodic table: not many people memorise it, but if they understand the structure, they have an idea of what's what.