An Etymological Dictionary of Astronomy and Astrophysics

A hypothetical small planet proposed in the 19-th century to exist in an orbit between Mercury and the Sun. In order to explain some characteristics of Mercury’s orbit, the French astronomer Urbain Jean Joseph Le Verrier (1811-1877) hypothesized the presence
of another planet, which he named Vulcan. Those particularities of Mercury’s orbit were later explained by Albert Einstein’s theory of general relativity.

See also: L. Vulcanus in Roman mythology the blacksmith god of fire and volcanoes, a word of Etruscan origin