[ExI] new ninth?

[John Clark]

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.

 John K Clark
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