Aspiring hard-scifi writer here. I try to make sure details in my fiction are consistent with known science or reasonable extrapolations thereof, unless absolutely demanded by the plot (and even then I try to offer some justification). I'm wondering if the solar system I'm setting a short story in would be stable over several billion years, long enough for intelligent life to evolve: Primary is a red dwarf star of around one quarter solar mass. Orbiting it is a brown dwarf of 25-40 Jupiter masses at a distance of say 50-100 million kilometers, and orbiting that is a planet (according to the IAU it's still a planet even though it's orbiting a failed star) of around a tenth Earth's mass with around a third the volume, say two million kilometers out- far enough out, from my sloppy estimation, to be quite cold on the surface, but close enough to have become tidally locked relatively early in its history and for those tidal forces to heat a subsurface ocean. Achieving a Europa-like effect, essentially, in a very different system. Does this work?