Sorry Paul, but I should have expanded on my little comment. My apologies
What I was trying to say was supposed to be an answer to Terry's question about what would make Jupiter start a nuclear reaction. In order for Jupiter to start hydrogen fusion, all you would theoretically need would be to add more mass to it - ie. Hydrogen. A star can only form if it has a certain critical mass (not sure what it is but it would be more than Jupiter's mass obviously, and more than a brown dwarf). If a rotating mass of hydrogen is massive enough, it will contract and collapse, thus causing the hydrogen to ignite and then a star would form.
I hope that explains my previous post.