Vulcan (hypothetical planet) Vulcan (hypothetical planet) Vulcan is a small hypothetical planet that was proposed to exist in an orbit between Mercury and the Sun. Attempting to explain peculiarities of Mercury's orbit, the 19th-century French mathematician Urbain Le Verrier hypothesized that they were the result of another planet, which he named "Vulcan". A number of reputable investigators became involved in the search for Vulcan, and despite occasional claimed observations, no such planet was ever confirmed. Peculiarities in Mercury's orbit have now been explained by Albert Einstein's theory of general relativity. Searches of data gathered by NASA's two "STEREO" spacecraft have failed to find
Planet Nine require a relatively close encounter with Planet Nine, however, which becomes less likely at large distances from the Sun. Planet Nine does not have an official name and will not receive one unless its existence is confirmed, typically through optical imaging. Once confirmed, the International Astronomical Union will certify a name, with priority usually given to a name proposed by its discoverers. It is likely to be a name chosen from Roman or Greek mythology. In their original article, Batygin and Brown simply referred to the object as "perturber", and only in later press releases did they use "Planet Nine".