While Jupiter is nowhere near massive enough to initiate fusion in its core, there are even more massive objects out there that fall short of that achievement, and they are called brown dwarfs. Brown dwarfs have a mass that places them between giant planets and small stars. They were only recently discovered in the 1990s, but thousands are now known. More massive ones can fuse deuterium, and even lithium, but not hydrogen, distinguishing them from normal stars.