Urbain Le Verrier, an astronomer and mathematician, sat down in 1846 and sought to discover a planet that had never been observed by mankind before. Uranus (grow up) had been travelling in unanticipated directions, as predicted by Newtonian gravity theory.
Though the differences were minor, there was a mismatch between Uranus’ observed orbit and the way Newtonian physics predicted its orbit. In July, Le Verrier argued that the discrepancy may be explained by another planet beyond Uranus, and provided predictions about its orbit.
He wasn’t interested in finding it using a telescope now that he’d identified it in algebra, and the duty of hunting for it was left to German astronomer Johann Gottfried Galle. On September 23, 1846, Galle examined the location predicted by Le Verrier and discovered that it was within 1 degree of the planet Neptune.
Don’t worry, we’re on our way to Spock’s planet.
So, after discovering a new planet by studying the orbit of another, Le Verrier was asked to investigate a planet whose name does not also mean butthole: Mercury. Mercury is the most difficult planet in our Solar System to view because it is so close to the Sun (assuming there is no Planet Nine out there). Le Verrier was given the task of calculating Mercury’s orbit using Newtonian physics.
He couldn’t, however. Mercury’s eccentric orbit made no sense to him, no matter how hard he tried. According to Newtonian theory, the planets move in elliptical orbits around the Sun, but studies revealed that Mercury’s orbit wobbles more than the gravity exerted by the other known planets could account for.
He felt that, like Uranus, this was due to another planet disrupting the planet’s path. He eventually named the planet Vulcan after the Roman god of fire, as he was a great Star Trek fan.
Soon after, astronomers began to report observations of this planet, the first of which was made on March 26, 1859 by Edmond Modeste. When he saw an article about his work nine months later (he was, at best, an amateur astronomer), he notified Le Verrier. Based on Modeste’s observations, Le Verrier computed the planet’s anticipated orbit, which he predicted would transit two to four times per year.
Others claimed to have seen Vulcan, but this may be explained by sunspots, known planets, or studies of surrounding stars. Le Verrier updated his estimates based on more sightings, but it was never seen in any way that could be described as concrete.
However, the planet was not a passing craze, but lasted for over 70 years. Based on estimates by renowned astronomer Theodor von Oppolzer, newspapers reported in 1879 that Vulcan would transit the Sun. It never appeared. It was looked for during almost every eclipse during this time period, but it was never found.
So, why didn’t you learn about Vulcan while studying the eight planets? Because it didn’t exist at all. The planet created by Le Verrier through mathematics was undone by a new physics theory: Einstein’s theory of general relativity.
Einstein’s theory predicted Mercury’s journey without any extra planets interfering with its wobble. Gravity, according to the idea, is caused by the curvature of spacetime caused by massive objects, with objects closer to the large objects being more affected. The idea could explain the shifting, or wobble, of Mercury’s orbit, whereas the outer planets, which are less impacted by curvature, are minimally influenced by the new estimates, given their distance from the Sun.
As a result, Einstein’s theory could explain both Mercury’s orbit and the orbits of Earth, Mars, Jupiter, and other planets without the use of other planets. Planet Vulcan has died.