Whats the exact difference between a large Jupiter and a brown dwarf?
The distinction is not crisp: there’s a kind of continuum between jupiters and brown dwarfs. Anything with less than about 8% of a solar mass can’t sustain fusion, and can be considered a failed star. Jupiter has only about 0.1% of a solar mass. An object with less than about ten times Jupiter mass might be considered a planet; objects more massive than that than could be considered brown dwarf stars (objects with more than about 13 times the mass of Jupiter may have had some limited nuclear fusion reactions happening in their early lives, but which did not last long).
