Hi Gary

Cool thing about Jupiter is just how close it is to the maximum radius for a cosmic-ratio H/He mix. If you want to visualise a brown-dwarf just look at Jupiter for scale. Even mimimum mass red-dwarfs are within 25% of Jupiter's radius. Which brings up the interesting thing about brown-dwarfs - even hot ones will have really, really nasty gravity.

A radius of Jupiter and 50 times the mass, for example, means 65 times the density of water and ~ 125 gee surface gravity. Gets worse as the thing cools and contracts over the billennia. A poster on a different board wanted to argue that HD28185b - which orbits in a near circular orbit in its primary's ecosphere - could be a super-Earth and thus habitable. I knew that this was wildly in error because of core-compression. The planet masses a minimum 5.6 Jupiters, and if it was pure iron would have a radius of ~ 12,000 km. Nasty, nasty surface gravity of ~ 500 gee.

Would make for a good "Earth-like" Mesklin-style habitat if it spun fast enough though.

Adam