Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth. Brown dwarfs occupy the mass range between that of large gas giant planets and the lowest-mass stars; this upper limit is between 75 and 80 Jupiter masses . Currently there is some debate as to what criterion to use to define the separation between a brown dwarf and a giant planet at very low brown dwarf masses (~13), and whether brown dwarfs are required to have experienced fusion at some point in their history...