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The mystery of the planet Vulcan

This article was first published in the November/December issue of IQ, the exclusive magazine for Mensa members. Find out more about becoming a Mensa member here. 

 

Words: Katie Cutforth 

Delve into another fascinating scientific theory that no longer cuts the mustard 

Star Trek fans will know it as the fictional home of Vulcanians, but Vulcan was also the name of a hypothetical planet that many astronomers believed in up until the early 1900s. Vulcan was thought to be an ‘intermercurial’ planet, a celestial body in orbit between Mercury and the Sun.  

The idea of an intermercurial planet was the subject of speculation among scientists as far back as the 17th century, with many supposed sightings reported by stargazers over the centuries. Despite being widely accepted, Vulcan was never concretely observed. So how did the brightest minds in astronomy come to believe in the existence of this mythical planet? 

It began in 1846, when the French astronomer and mathematician Urbain Le Verrier successfully predicted a planet using theory alone. Noting small discrepancies in the observed orbit of Uranus compared with the motion predicted by Newtonian physics, Le Verrier proposed that this irregularity could be explained by the existence of another planet beyond Uranus.  

Later that year, German astronomer Johann Gottfried Galle observed the location in which Le Verrier had predicted there would be a planet and found – within a degree of the spot he had identified – the planet Neptune.  

Buoyed by this discovery, Le Verrier set out to investigate the innermost planet in the solar system – Mercury. Even today, Mercury remains the most difficult planet of the solar system to observe from Earth due to its small size and close proximity to the Sun.  

By 1859, Le Verrier had observed peculiarities in Mercury’s orbit and predicted that they too were caused by the gravitational influences of an unknown nearby planet. Having proven the reliability of his methods with the discovery of Neptune, and with further reports of a celestial object passing between Mercury and the Sun that same year, Le Verrier announced he had finally identified the long sought-after planet, which he named Vulcan after the Roman God of fire. 

Belief in Le Verrier’s Vulcan endured for more than 70 years, with reported sightings of the planet only increasing following the announcement. However, no definitive observation was ever recorded – and Vulcan remained the stuff of theory and mathematics.  

Albert Einstein’s 1915 theory of general relativity is what eventually decried Vulcan’s existence. It successfully explained that the discrepancies in Mercury’s orbital motion resulted from the warping of spacetime around the Sun, eliminating the need for Le Verrier’s hypothetical planet.  

Einstein’s theory was empirically verified by the Eddington experiment that took place during the solar eclipse of 29 May 1919. Astronomers successfully photographed the stars around the Sun during totality, showing they were in the position as predicted by general relativity. Einstein became an overnight celebrity, general relativity became widely accepted, and the existence of another inner planet was ultimately disproved. Finally, the mysterious Vulcan was consigned to science fiction.


Main image: An 1846 lithography of the Solar System showing a hypothetical Vulcan. Pic credit: E. Jones & G.W. Newman/Library of Congress

The mystery of the planet Vulcan

This article was first published in the November/December issue of IQ, the exclusive magazine for Mensa members. Find out more about becoming a Mensa member here. 

 

Words: Katie Cutforth 

Delve into another fascinating scientific theory that no longer cuts the mustard 

Star Trek fans will know it as the fictional home of Vulcanians, but Vulcan was also the name of a hypothetical planet that many astronomers believed in up until the early 1900s. Vulcan was thought to be an ‘intermercurial’ planet, a celestial body in orbit between Mercury and the Sun.  

The idea of an intermercurial planet was the subject of speculation among scientists as far back as the 17th century, with many supposed sightings reported by stargazers over the centuries. Despite being widely accepted, Vulcan was never concretely observed. So how did the brightest minds in astronomy come to believe in the existence of this mythical planet? 

It began in 1846, when the French astronomer and mathematician Urbain Le Verrier successfully predicted a planet using theory alone. Noting small discrepancies in the observed orbit of Uranus compared with the motion predicted by Newtonian physics, Le Verrier proposed that this irregularity could be explained by the existence of another planet beyond Uranus.  

Later that year, German astronomer Johann Gottfried Galle observed the location in which Le Verrier had predicted there would be a planet and found – within a degree of the spot he had identified – the planet Neptune.  

Buoyed by this discovery, Le Verrier set out to investigate the innermost planet in the solar system – Mercury. Even today, Mercury remains the most difficult planet of the solar system to observe from Earth due to its small size and close proximity to the Sun.  

By 1859, Le Verrier had observed peculiarities in Mercury’s orbit and predicted that they too were caused by the gravitational influences of an unknown nearby planet. Having proven the reliability of his methods with the discovery of Neptune, and with further reports of a celestial object passing between Mercury and the Sun that same year, Le Verrier announced he had finally identified the long sought-after planet, which he named Vulcan after the Roman God of fire. 

Belief in Le Verrier’s Vulcan endured for more than 70 years, with reported sightings of the planet only increasing following the announcement. However, no definitive observation was ever recorded – and Vulcan remained the stuff of theory and mathematics.  

Albert Einstein’s 1915 theory of general relativity is what eventually decried Vulcan’s existence. It successfully explained that the discrepancies in Mercury’s orbital motion resulted from the warping of spacetime around the Sun, eliminating the need for Le Verrier’s hypothetical planet.  

Einstein’s theory was empirically verified by the Eddington experiment that took place during the solar eclipse of 29 May 1919. Astronomers successfully photographed the stars around the Sun during totality, showing they were in the position as predicted by general relativity. Einstein became an overnight celebrity, general relativity became widely accepted, and the existence of another inner planet was ultimately disproved. Finally, the mysterious Vulcan was consigned to science fiction.


Main image: An 1846 lithography of the Solar System showing a hypothetical Vulcan. Pic credit: E. Jones & G.W. Newman/Library of Congress

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