>> The article I read doesn't consider "Sedna" a planet. But then the
>> scientists they interviewed don't consider Pluto a planet either!
>
>Indeed. That's why I said
>
>> > At 3/4 the size of Pluto, if you count Pluto as a planet you (arguably)
>> > have to count Sedna as one as well.
>
>Pluto has  a diameter of 2300 km and Mercury 4900 km so Pluto is about 50%
>dia or about 10% the volume of Mercury. Who decides where "real" starts?

Well, my idea is that if that big ball formed around the Sun, it's a planet.
If it instead formed around a planet, it's a satellite (i.e. a "sub system").

As far as I recall Pluto was probably just a moon of Neptune that (because of
a gravitationial perturbation due to some other moon) escaped Neptune's orbit,
getting its own orbit (which still crosses Neptune's one, BTW).

But I'm not astrophysic.. so what for me "should" be a planet or a satellite
is no law or rocket science. :)

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu