If Jupiter was a failed star, it failed big time. "Although Jupiter would need to be about 75 times more massive to fuse hydrogen and become a star,[66] its di

If Jupiter was a failed star, it failed big time. "Although Jupiter would need to be about 75 times more massive to fuse hydrogen and become a star,[66] its diameter is sufficient as the smallest red dwarf may be only slightly larger in radius than Saturn." It got as big as it could be, though. "Theoretical models indicate that if Jupiter had over 40% more mass, the interior would be so compressed that its volume would decrease despite the increasing amount of matter. For smaller changes in its mass, the radius would not change appreciably.[63] As a result, Jupiter is thought to have about as large a diameter as a planet of its composition and evolutionary history can achieve.[64] The process of further shrinkage with increasing mass would continue until appreciable stellar ignition was achieved" https://en.wikipedia.org/wiki/Jupiter https://en.wikipedia.org/wiki/Jupiter