Learn a Thing Today: Have We Found Planets Using Math?

Planets Found by Math

Urbain Le Verrier

Ancient peoples have always known about Mercury, Venus, Mars, Jupiter and Saturn because you can easily see them with you eyes. The discovery of Uranus was the first time a planet was found that needed the aid of a telescope to be see. William Herschel discovered this planet in 1781.

In the next century, another planet was discovered, and this one was discovered in a very interesting way. The credit for finding planets is usually thought to go to the first person to point their telescope at it, but this case is a little different. In the 1845, Urbain Le Verrier looked very closely at the orbit of Uranus, and discovered it to be slightly off from what was known from Kepler about planetary motion. Soon after, he had a hypothesis that another planet beyond the orbit of Uranus could account for the perturbations in the orbit he observed. Le Verrier contacted Johann Gottfried Galle at the Berlin Observatory and told him to point his telescope at a particular location at a particular time to look for this eighth planet.

Johann Gottfried Galle

Sure enough, when Galle peered through the telescope lens on September 23^rd in 1846, there sat Neptune, 1° away from Le Varrier's predicted position. Interestingly, the director of the Cambridge observatory, James Challis, later realized he too had seen Neptune on two separate occasions before that, but failed to recognize it as a planet.

This, however, was not the only planet found by math. Later on, small perturbations were noticed in the orbit of the planet Mercury, again by Le Verrier. A small planet was hypothesized, this time inside the orbit of mercury, too close to the sun to see. This theorized planet was given a name – Vulcan.

Yes, the one and same, though the hypothesized planet came before the Star Trek series by more than a century (and was the Roman god of fire, volcanoes, and metalworking well before that). This planet does not actually exist. We have since sent spacecraft close enough to the sun to see any potential Vulcanoids, and to date have found none. So what of the perturbations of the Mercurial orbit? The answer is relativity. Because Mercury is so deep in the sun's gravity well, it experiences relativistic affects, and this accounts perfectly for the precession observed in its orbit.