Pluto was discovered long before it was discovered. That is, its existence was hypothesized based on the inconsistencies in the orbits of surrounding planets Uranus and Neptune. Some other large mass had to exist to exert enough gravity to alter those orbits. The astronomer Percival Lowell, who first proposed the existence of the extra planet, called it Planet X and began a decade-long search for it; but with the current state of technology allowing him to survey just small portions at a time, it was equivalent to searching for a needle in a haystack.

On this day, February 18, in 1930, the mysterious “Planet X,” also known as Pluto, was finally observed at the Thomas Lowell Observatory in Arizona, where Lowell began his search several decades earlier.

A survey went out subsequent to the discovery, asking for suggestions for the planet’s new name. “Pluto” came from an 11-year-old schoolgirl in England named Venetia Phair. She did not have a specific reason for choosing “Pluto” as the name, but it stuck anyway because it contained the P-L initials of Percival Lowell, as well as referring to the Greek god of the underworld who could remain invisible, as the planet was, for periods of time.