Vulcan (hypothetical planet), a hypothetical planet once thought to be between Mercury and the Sun; Vulcanoid, a hypothetical population of asteroids between Mercury and the Sun; Vulcan (programming language), a programming language, now known as dBase; Vulcan laser, a laser at the Rutherford Appleton Laboratory, England

Phaeton (alternatively Phaethon or Phaëton) (/ ˈ f eɪ. ə θ ən /; Ancient Greek: Φαέθων, romanized: Phaéthōn, pronounced [pʰa.é.tʰɔːn]) was the hypothetical planet hypothesized by the Titius–Bode law to have existed between the orbits of Mars and Jupiter, the destruction of which supposedly led to the formation of the asteroid belt (including the dwarf planet Ceres).