On Sun, Oct 16, 2016 at 06:17:07PM -0400, Christopher Sean Hilton wrote:
> Secondly, as I look at extended systems, I find that there are many
> that feature neither fluid nor "ice" nor gas giants. In such a system
> I would figure that the only source of hydrogen would be the Oort
> Cloud.

Most bodies of any reasonable size outside the "ice line" are going to
have hydrogen compounds either on the surface or just beneath,
including a lot of water ice.  Colder ones are also likely to have
methane and ammonia.

Hydrogen is by far the most common element in the universe.  If a
planet or other body has little hydrogen, it is because something
removed it.  Usually that is heating above water's melting point for
billions of years, with consequent loss of water vapour.  Even Mars, a
dry planet with a very thin atmosphere and occasionally warm enough to
lose water through evaporation and UV dissociation, has a lot of ice
just under the surface.  Essentially every major body further out has
even more.

Even if a system generation program says that some body in the outer
system is rocky, it should almost always realistically be rocky with a
lot of ice either on the surface or just below it.

- Tim