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Vulcan: the planet that never was

This blog has frequently lamented the demotion of Pluto. After being expelled from the company of planets, it now resides in the newly-named Plutoids, in the company of Eris, Sedna and other dwarf planets. Another one-time planet suffered a worse, and lonelier, fate one hundred years ago.

The planet Vulcan came into (theoretical) being as a solution to the problem of Mercury‘s orbit, which deviated from the track that Newton’s laws laid down for it.

It worked before…

The planet Uranus had also showed some eccentricities of orbit, which had been resolved by hypothesizing another planet (Neptune) whose gravitational pull caused the anomalies. So it seemed reasonable that another planet must be affecting Mercury, too.

This all began with the French astronomer Urbain Le Verrier, who was studying the orbit of Mercury, first working out the mathetmatics, then tracking the transits of Mercury across the sun. (During a transit it would show up as a black dot against the sun, making the tiny planet easier to see and follow.) The observations didn’t tally with Le Verrier’s numbers, and he went back to his desk to try again.

However, when he published his second try in 1895, the numbers still were out slightly, and he suggested a second object was influencing Mercury’s orbit.

Finding Vulcan

Le Verrier became extremely excited when an amateur astronomer named Lescarbault contacted him claiming to have observed an object near the sun, a black dot moving in the same way as Mercury had during its transit. This had to be Vulcan, Le Verrier insisted, and such was his reputation that he was believed.

He did some calculations, and estimated that based on Lescarbault’s observations, the new planet must orbit the sun in 19 days and 17 hours. He named it Vulcan, after the Roman god of fire, especially destructive fire.

This was the beginning of the hunt for Vulcan, a search that continued, as people spotted various objects that turned out to be sunspots, stars that had been in the same part of the sky as the sun, and asteroids from the Apollo group (so called because their orbit is elliptical, taking them in past Earth).

Le Verrier, however, was undaunted. As the Hypothetical Planets website says:

In 1860, there was a total eclipse of the Sun. Le Verrier mobilized astronomers throughout the world to find Vulcan. No one did. Wolf’s suspicious ‘sunspots’ now revived Le Verrier’s interest, and additional ‘evidence’ found its way into print just before Le Verrier’s death in 1877. On April 4, 1875, German astronomer H. Weber saw a round spot on the Sun. Le Verrier’s orbit indicated a possible transit on April 3 that year. Wolf noticed that his 38-day orbit also could have performed a transit at about that time. That ’round dot’ also was photographed by astronomers in Greenwich and Madrid.

There was one more flurry of sightings after the total solar eclipse on July 29, 1878. Two observers claimed to have seen small, illuminated disks in the vicinity of the Sun, objects which could only be small planets inside Mercury’s orbit. J.C Watson, professor of astronomy at the University of Michigan, believed he had found two intra-Mercurial planets. Lewis Swift (co-discoverer of Comet Swift-Tuttle, which returned in 1992), also saw a ‘star’ he believed to be Vulcan. However, it was in a different position than either of Watson’s two ‘intra-Mercurials.’ Neither Watson’s nor Swift’s sightings could be reconciled with Le Verrier’s or Lescarbault’s ‘Vulcan.’

The End of Vulcan

Two scientists killed the Vulcan hypothesis: W. W. Campbell produced a paper in 1909 which pointed out that in 20 years of photographing the sun in clear skies, no planet Vulcan had appeared; and Einstein produced one of his most famous papers in 1915, showing that general relativity could account for the peculiarities in Mercury’s orbit. (The Mercury paper provided a test of his theories as well, which Einsteinian general relativity passed.)

And now, 100 years later, some scientists now think there may be a belt of asteroids between the sun and Mercury, which they are calling vulcanoids. These asteroids, if they exist, would be leftovers from the formation of the planets. So far, however, NASA’s Messenger probe and the solar observatories have found nothing. (But Le Verrier’s ghost is following developments.)


Vulcan. Bronze statuette, Roman work, 1st century AD? (Wikimedia)
Vulcan. Bronze statuette, Roman work, 1st century AD? (Wikimedia)

Vulcan was one of Rome’s oldest gods; his cult dated back to the kings of Rome, and one of his temples, the Vulcanal, was at the foot of the Capitoline Hill. His other major temple was located outside the city, on the advice of Etruscan haruspices. This was probably wise, because Vulcan, who gave his name to volcanoes, was the god of dangerous fire.

Two of his by-names, Quietus and Mulciber (Fire Allayer), come from his power to avert fires. Events like the Burning of Rome in 64 CE showed his usefulness; like all ancient cities, Rome burned with disturbing ease.

Vulcan’s power extended over the blacksmith’s forge, lightning, raging fires, and volcanoes. The Volcanalia, on August 23rd, was his festival, when heads of households threw small fish into the fire. People also hung their clothes out in the sun, which suggests a connection between Vulcan and the sun-god Sol.

Fun Stuff

And finally, some Vulcan trivia:

  1. The Vulcan Le Verrier sought is not the same as Mr. Spock’s Vulcan, which is located in the constellation Eridanus. It’s a satellite of Eta Eridani, to be precise.
  2. If you’ve ever seen a mention of Vulcan in a book on astrology or esotericism and wondered why, it’s because a lot of them draw on Alice Bailey‘s work, and when she was writing her 1916 book Esoteric Astrology, Einstein had just formulated his explanation of Mercury’s orbit the year before. She probably didn’t know that Vulcan had been superseded as an explanation of Mercury’s peculiarities.


Baum, Richard and Sheehan, William, In Search of Planet Vulcan: the Ghost in Newton’s Clockwork Universe, Plenum Press, New York, 1997.
McGrath, Sheena Sun, Moon and Stars, Capall Bann, 1997.


National Georgraphic article on Vulcan
Guide to the Universe page on Vulcan
Hypothetical Planets website

Astrological Significance of Vulcan

Wikipedia entry on the god
Vulcan and the Volcanalia


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