http://www.physorg.com/news91889915.html
In paragraph 7, defining Pluto"s status, the article says
"...comets are defined by the fact that they have tails..."
I am pretty sure that this is not how comets are defined. You won"t have much luck finding tails on /anything/ a billion miles from the Sun.
The article did slip a little there. Most lumps of rock if they are big enough and come close to the sun could qualify as a comet but Pluto was/is in a fixed though odd orbit so was never going to come close enough. Runaway moon would have been a better term (though we now know it to be orbited by moons itself.) Had it been a lot closer it may have been called an asteroid as Ceres is 580 miles across.
I think he was stating that that was how comets were defined *then*. They only knew about 3 different kinds of moving objects: Planets, Comets, and Asteroids. Asteroids were all between Jupiter and Mars (by their definition), and comets were little things that came near the sun and flared up. Therefore, by the process of elimination, Pluto had to be a planet.
It's kind of strange that it never occurred to them to create a new class of object
It's kind of strange that it never occurred to them to create a new class of object