Vulcan is a hypothetical planet that was once believed to exist within our solar system, specifically between the orbits of Mercury and the Sun. The idea originated in the 19th century when astronomers sought to explain peculiarities in Mercury's orbit that could not be accounted for by Newtonian physics. Despite extensive searches, no evidence of Vulcan was ever found, and the concept was eventually discarded after Albert Einstein's theory of general relativity provided a more accurate explanation for Mercury's orbital behavior. Today, Vulcan is often referenced in discussions about scientific theories and the evolution of astronomical understanding.