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

Phil Plait
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