Pluto the underdog

Café
#1

@Scott_Sauyet said elsewhere:

Abso-*******-lutely. And while we’re at it, Charon should be up-graded.

  • If it’s oblate or otherwise near-spherical

  • Has largely cleared its orbital path (regardless of its orbital shape or plane)

  • Is a satellite of its host star

then it’s a planet, dammit.

And really, if “they” are gonna get so picky, Earth isn’t a “true planet” either. The Earth–Moon size/mass ratios are so high, it’s practically a binary system, especially compared to all known planet–moon and exoplanet–exomoon ratios. Together they cleared our orbital path, not Earth alone.

<sigh/>

Irreverent footnote, channeling Douglas Adams:

According to the Department of Planetary Pedantry, Earth and Moon technically qualify as a gravitationally bound, co-dominant pair. This reclassification would retroactively demote Earth to “primary body of a binary system,” which, while accurate, is unlikely to fit on classroom posters or NASA merch. And surely, If the IAU ever admits the Earth–Moon system is binary, expect a sudden surge in Moon citizenship applications.

I, for one, welcome it. :nerd_face:

The reclassification of Earth as part of a binary system will, of course, be hotly debated at the 42nd Interplanetary Congress (next year), assuming no one invites the Vogons who will inevitably ruin everything with endless poetry claiming it’s just paperwork.

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#2

I’m a fan of this argument:

tl;dr:

  • as far as Planetary scientists are concerned, Pluto is a planet, and they completely ignore the IAU’s classification
  • the IAU’s attempt to do science by voting was a deeply embarrasing debasement of science
#3

I dont know what the fuss is about, Pluto remains a “Dwarf Planet”, it still has “planet” in the description. If you simply say planet its implied you are only refering to the greater planets, but it does not stop Pluto from being one. I am comfortable with Pluto being in the group of “Dwarf Planets”, and before anyone gets negative I suggest you stop and consider other “Dwarf Planets” that also have a right to be “Dwarf Planets”.

#4

the problem is the IAU definition is bonkers[18].

Despite both “planet” and “dwarf planet” having “planet” in the name, the IAU consider them genuinely distinct classes of objects. ie, they don’t mean “dwarf planet is a subset of planet”, they mean “planet” and “dwarf planets” are exclusionary sets.

Planetary scientists DO consider “dwarf planets” to be a type of planet, and consider Pluto to be one of them.

[18] Their first criteria for planet locks it into our OWN solar system. So apparently there is no such thing as planets anywhere else in the universe. And their third is about clearing the orbital neighborhood - which is [a] time based, and [b] not an property inherent to the object itself, but inherent to the system it’s in. Plus “cleared” is poorly defined.

#5

Similary I would think an Exoplanet is still “a planet” as well, sounds a bit silly.

Then, one day we may be in another solar system and we could not call them exoplanet, exo (Except if humanity destoys itself which is on the cards).

Perhaps the are IAU is just attention seeking?

#6

I dont think they’re attention seeking per se, I just think their priorities make it difficult for them to categorise planets sanely.

Astronomers almost by definition, care about where things are.

The definition of a planet, otoh, I think is more about what it is, and that’s all (and afaict, that’s the view of planetary scientists). It’s location (in our solar system, in another solar system, or a wanderer between solar systems) and what’s near it - are irrelevant.

#7

I am very much in the same boat as the astronomers, as I am a bit of an amateur theoretical cosmologist, :nerd_face: but with this silly public argument I think they can just leave it alone.

#8

Marvin says: “they are also the worst marksmen in the galaxy.”

Q: Are the Vogons vegans?

Just asking
TT

p.s. A Vogon poetry reading ...

Screenshot 2025-10-24 10.01.05

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#9

For that comment you should, at least, get the Constellation Prize.

#10

But hey, they got the second criteria right, didn’t they? How does that song go, “one out of three ain’t bad”? Something like that? Or am I having another off-by-one error?

#11

Could be. Off-by-one is not exclusive to the IAU.

<chuckles>