On this day in 1860, French mathematician Urbain le Verrier announced the discovery of a planet called ‘Vulcan’ to the French Academy of Sciences. The planet supposedly is between Mercury and the Sun, and was conceived of in response to an anomaly in Mercury’s orbit. We now know that this anomaly can be explained by Einstein’s theory of relativity. Le Verrier was heavily involved in the discovery of Neptune, and insited until his death that Vulcan exists.
It is now no longer widely believed that Vulcan exists. The only place planet Vulcan exists is in the Star Trek universe, where it is the home planet of Spock.