Urbain Le Verrier and the hypothetical Planet Vulcan

Urbain Le Verrier
(1811 – 1877

On 2 January 1860, French astronomer Urbain Le Verrier announced the discovery of Vulcan, a hypothetical planet inside the Mercury orbit, to a meeting of the Académie des Sciences in Paris. Despite the lack of any reliable observation, Le Verrier really was convinced until his death that he had discovered a new planet. It was Einstein’s special theory of relativity and a completely new understanding of the laws of gravity that modified the predicted orbits of all planets and solved the problem of the hypothetical intra-mercurial planet.

Urbain Le Verrier enrolled at the École Polytechnique to study chemistry, but switched to astronomy shortly after and started working at the Paris Observatory. In later years, he became the institution’s Director. In September 1839, Le Verrier presented his first work to the Académie des Sciences ‘On the Secular Variations of the Orbits of the Planets‘. In it he discussed the question of the Solar System’s stability, building on the work of Pierre-Simon Laplace. After a few works and observations on comets, Le Verrier began using mathematical knowledge and astronomical observations of planet Uranus to predict the then unknown planet Neptune. In his calculations, he noticed systematic discrepancies between Uranus’ orbit and Newton’s laws of gravity and was able to predict the planet’s position. As Le Verrier’s work on the planets continued, he published the ‘Annales de l’Observatoire de Paris‘, tables of the motions of all of the known planets, releasing them as he completed them, starting in 1858. This was, next to his role in the discovery of Neptune one of his most influential works.

Starting in 1843, Le Verrier began studying planet Mercury and was the first to report that it was not possible to explain its orbit’s slow precession by Newtonian mechanics. The scientist announced that there must be another planet in an orbit even closer to the Sun than that of Mercury. Since Le Verrier earned himself a good reputation among contemporary scientists and due to his success on the search of Neptune, this explanation seemed somewhat trustworthy. This hypothetical planet was then titled ‘Vulcan’. This name was chosen because it stood for the god of beneficial and hindering fire, including the fire of volcanoes, making it an apt name for a planet so close to the Sun.

As Urbain Le Verrier came up with the extraordinary theory, the search for Vulcan began. The amateur astronomer Edmond Modeste Lescarbault claimed to have seen the planet’s transit in 1859 and after a short visit and confirmation by Le Verrier, the news of the discovered Vulcan spread quickly. However, not every scientist accepted the discovery like Emmanuel Liais, who claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault’s at the very moment that Lescarbault said he observed his mysterious transit. Liais, therefore, was “in a condition to deny, in the most positive manner, the passage of a planet over the sun at the time indicated“. Still, Le Verrier calculated the planet’s orbit based on Lescarbault’s observation and more and more amateur astronomers as well as scientists mailed Le Verrier and claimed to have noticed Vulcan’s transit as well.

Unfortunately, Urbain Le Verrier passed away in 1877, convinced of having discovered another planet, but as the search of the planet continued most astronomers began to doubt its existence. Only in 1915, the problem could be solved by Albert Einstein‘s theory of relativity, which was an entirely different approach to understanding gravity compared to classical mechanics according to Newton. With his equations, the exact observed amount of advance of Mercury’s perihelion without any recourse to the existence of a hypothetical Vulcan could be predicted.

An explanation to the many false ‘observations’ may be the fact that in order to observe Mercury, the telescope must be pointed very close to the Sun, where the sky is never black and the huge amount of light present even quite far away from the Sun can produce false reflections inside the optics, thus fooling the observer into seeing things that do not exist. As most scientists gave up the search for Vulcan after 1915, some search for the hypothetical planet until this day.

At yovisto, you may enjoy a video lecture by Professor Ian Morison on the Search for Planet X.

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