A hypothetical planet whose orbit is said to lie between Mercury and the Sun, about twelve million miles from the Sun. Astronomers have no evidence of this planet as yet.
A hypothetical planet supposed to lie inside the orbit of Mercury, but always on the opposite side of the Sun from the Earth, making it invisible. Originally postulated to account for perturbations in planetary orbits, this planet is no longer supposed to exist by science, although some astrologers claim it as a sort of spiritual entity having power in a horoscope.
Vulcan is an intra-Mercurial planet orbiting the Sun every 18.6 days. The nature of Vulcan is combustible, fiery, explosive, and ethereal. Vulcan rules wind conditions, gases, gas-producing combustible materials like petrol and gun-powder etc. The existence of Vulcan has never been confirmed scientifically.