What percentage of the Solar System is the Sun?

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What is the history of Planet Vulcan? - and, no, not the one in Star Trek!

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What is the history of Planet Vulcan? - and, no, not the one in Star Trek!


Planet Vulcan was a hypothetical planet thought to exist between Mercury & the Sun until Einstein’s General Relativity explained Mercury’s strange orbit.



In 1846 French Mathematician Urbain Le Verrier was successful in predicting the path of Neptune based on perturbations of Uranus. As a result of this Astronomers were able to “discover" the planet later that year.

Building on his success with Neptune Le Verrier turned his attention to the strange, elongated, orbit of Mercury which did not conform to Newton’s laws of motion, which, at the time, were used to explain the motion of all the planets.

In 1859 Le Verrier published a study of Mercury’s orbit and his model included a planet between the Sun & Mercury that would explain the perihelion precession of Mercury.

He named this planet Vulcan after the Roman god of beneficial fire, including volcanoes, as the planet would be so close to the Sun.

As a result Astronomers started looking for Vulcan in earnest and, of course, many claimed to have found it!

Le Verrier himself died in 1877 convinced that he had discovered another planet.

It was only after Einstein published General Relativity in 1915, that precisely predicted the orbit of Mercury with our needing another internal planet, that we knew conclusively that Vulcan did not exist.

We do, however, still look for Vulcanoid objects orbiting the Sun between it and Mercury. Data from NASA’s two STEREO spacecraft has shown that it is very unlikely that there are any objects of 6km or more orbiting the Sun closer than Mercury but we have found Asteroid 2007 EB26 which is 700m wide and passes inside the Vulcanoid Zone.