Brown dwarfs are sub-stellar objects that are too low in mass to support a hydrogen-fusion reactions in their cores, which are characteristic of stars on the main sequence. Brown dwarfs are fully convective surfaces and interiors, with no chemical differentiation by depth. Brown dwarfs occupy the mass range between the large gas giant planets and stars the lowest mass, which upper limit is between 75 and 80 Jupiter masses (MJ). Currently, there is a debate on the criteria used to define the distance between a brown dwarf and a giant planet at very low mass brown dwarf (~ 13 MJ), and whether brown dwarfs are required to have experienced a merger point in their history. In any event, brown dwarfs heavier than 13 MJ do fuse deuterium and those above ~ 65 MJ also fuse lithium. Some planets are known to Orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144 b.