Vulcan is a hypothetical planet believed to lie between Mercury and the Sun. A few centuries ago, the planet was proposed after astronomers observed that Mercury had slightly changed its orbit with every revolution around the Sun.
In 1859, French astronomer Urbain-Jean-Joseph Le Verrier suggested that this was caused by the gravitational pull of an undiscovered planet lying between Mercury and the Sun. He called it Vulcan after the Roman god of blacksmithing. Le Verrier added that the planet could not be spotted because it was too close to the Sun.
A year later, amateur astronomer Edmond Modeste Lescarbault claimed to have spotted a small black dot near the Sun. Le Verrier said the dot was the planet Vulcan. Other astronomers later claimed to have spotted the elusive planet, although some insisted that they couldn’t see it.
Vulcan was soon considered the first planet of the solar system despite the lack of concrete evidence. This was probably because Le Verrier was an authority figure in astronomy. Thirteen years earlier, he had proposed Neptune after observing that an undiscovered planet was altering the orbit of Uranus. Besides, Vulcan’s existence was the only explanation for Mercury’s haphazard orbit.
This changed in 1915 when Albert Einstein’s Theory of General Relativity trashed every claim about the existence of Vulcan. Einstein said that massive objects like the Sun could bend time and space. Mercury’s orbit often changed because it was traveling through a “distorted space-time” caused by its closeness to the Sun.[