[ExI] new ninth?

Dan TheBookMan danust2012 at gmail.com
Mon Jan 25 18:51:32 UTC 2016

On Jan 25, 2016, at 10:31 AM, John Clark <johnkclark at gmail.com> wrote:
>> On Mon, Jan 25, 2016 at 11:47 AM, Dan TheBookMan <danust2012 at gmail.com> wrote:
>> ​> ​I don't see why the decision couldn't have been along the lines of:
>> There are three types of planets we now know of:
>> 1. Rocky ones like Earth and Mars,
>> 2. Gassy ones like Jupiter and Neptun, and
>> 3. Icy ones like Pluto.
>> I don't see why 1 plus 2 alone must be planets, must be where Nature made the joints, while 3 is not.
> The dividing line between planet and non-planet is always going to be somewhat arbitrary. I think astronomers were worried that if we included #3 as telescopes get bigger (no thanks​ ​to​ ​religious Hawaiians) we could end up with hundreds or even thousands of planets. And that's too many for third graders to learn.

That, sadly, does appear to have been the initial motivation.

And I agree that it seems arbitrary, though many distinctions are more taking a fuzzy boundary and setting a threshold. I've no problem with that, though, in this case, it seems like the threshold was gerrymandered to keep Pluto-like objects off any final tally of planets.


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