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Comment by Robotbeat | Hacker News Reader

If "Planet Nine" doesn't exist, that will be fitting Karma for those who proposed it, since they developed the new definition of planet specifically to exclude Pluto and any other planets like Pluto.

(I disagree with that definition as it made no consultation with planetary scientists who actually study planets.)

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I'm confused by your parenthetical, as the definition that excludes Pluto (and Eris) was arrived at by the International Astronomical Union (https://www.iau.org/).

IAU is made of astronomers (i.e. People who study stars and stuff), not so many planetary scientists (who specifically study planets).

I think it's fair to define planets based on an astronomical perspective; it's clear that Pluto, Eris and things like it, astronomically, belong to a different class than the other planets. Pluto is now classified as a dwarf planet. If we didn't "demote" it to a dwarf planet, then we would have to define a new term for the existing planets.

I am intrigued by your conspiracy theory and would like to subscribe to your newsletter. Why did they want to "specifically exclude Pluto"?

Pluto is notoriously different from the other eight planets, as can be explained in very elementary terms [1]. So, not to open any wounds, but the question is inevitably raised as to whether it is the same kind of "thing" as the other planetary bodies.

[1]. https://airandspace.si.edu/stories/editorial/pluto%E2%80%99s...

The actual planet itself is very active geologically and has a whole system of moons. The only reason you'd say it's very unlike the other 8 is due to orbital dynamics, i.e. due to other bodies besides itself. This is a strongly anti-planetary-science bias, IMHO.

Sooo... mass and composition are irrelevant? Because Pluto (and its fellows, like Eris) are smaller than a half-dozen moons. Pluto has less than _five percent_ of the mass of the smallest planet, Mercury. It is also mostly _ice_ unlike the inner (rocky) planets and the gas giants.

And variety of solar-system bodies are geologically active, from the inner planets, through numerous moons, down to comets and asteroids, and probably many other Trans-Neptunian Objects like Pluto (many of which also have moons). Your proposed criteria fail to be useful.

I don't follow. Planet Nine is not expected to be another dwarf planet like Pluto. There are a handful of other dwarf planets known already, some bigger than Pluto, and it's expected that there are hundreds more yet to be discovered.

Some may be bigger than Earth, yet still classed as dwarf planets. Therefore, I think the definition is BS as it has nothing to do with the planet itself (such as its geography, size, etc) but only the bodies around it.

You say "may be bigger than Earth", but I'm unaware of any dwarf planets that are bigger than Earth. Are there any? Assuming there are none, that's rather the point: bodies that large would tend to clear out their local zone.

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