Planets, planetary bodies, orbs...

On my website, I've written a classification scheme for solar system
objects. I want to make it as perfect as possible, so please send me
any possible scientific criticism.

My website: http://www.geocities.com/mad_scientist2064/
Classification: http://www.geocities.com/mad_scientist2064/sso.htm

I think that your classification makes a lot of sense! I would just make two
alterations:

- I would classify Io as a Selene. Io is basically an all-rocky world with
no atmosphere, and it looks so different from the Moon and from Mercury just
because it has that bunch of volcanoes spitting debris. But the volcanoes
are not exactly "intrinsic" to Io - they are just a side effect of Jupiter's
massive tides. Maybe Io would look nearly identical to Mercury if it were
located in a place with no gravitational stress.

- I'm not sure if Titan should be put with the other Cronus. First, it has
an atmosphere; second, according to infrared images taken in recent years,
it has a lot of "dark" and "light" areas that resemble continents and oceans
that in fact *may be* continents and oceans - made of liquid and frozen
methane and stuff like that ;-). So, I think that Titan should have its own
category.

- Finally, the 400 Km of diameter limit is kind of arbitrary. A rocky object
that size could still be very "edgy", while an icy object would be nearly
spherical. I think that the criterion should be sphericity, and not size.
(But maybe I'm way too contaminated by my idea of "orb". ;-)

Lucio Coelho