They used to come from Vulcanis.![]()
I sometimes wonder if the early TOS writers originally intended Spock to come from Le Verrier's Vulcan, a planet once hypothesized to exist inside Mercury's orbit and explain its orbital anomalies. It was discredited when Einstein's General Relativity accounted for the anomalies, but science fiction kept on using the idea for decades thereafter, so the creators of TOS were probably aware of it. And the original series pitch said Spock was "probably half-Martian," so they had Solar planets in mind as possible origins for him. Plus I don't think it's really until "Amok Time" that it becomes explicit onscreen that Vulcan resides in its own star system. ("The Man Trap"'s "Vulcan has no moon" might also be a clue, since Mercury and Venus are moonless and it follows that an cis-Mercurian Vulcan would have been also.) The first explicit mention of Vulcan as an extrasolar planet is actually in James Blish's "Balance of Terror" adaptation, where he makes a point of saying it's "not the imaginary Solar world of that name, but a planet of 40 Eridani."