

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" after he was satisfied by the sighting of supposed transit of Vulcan by physician named "Lescarbault".[1] Later the theoretical object got attention to explain why is there no mass between the orbit of Mercury and the Sun, but it was not found. The “anomalies” of Mercury were later explained by Einstein’s theory of relativity about a century later.
Despite the ruling out of Vulcan, there have been propositions of small objects that orbit the Sun within the orbit of Mercury. These are known as Vulcanoids, which may actually exist.