#39 Science in History
18th February 1930
Today in 1930, Clyde Tombaugh discovered the ninth planet in our solar system, Pluto.
Tombaugh was born in Streator, Illinois, in 1906. From an early age, he had a fascination with astronomy and spent countless hours studying the stars. In 1928, he sent a letter to Lowell Observatory in Flagstaff, Arizona, expressing his interest in astronomy and asking if they had any job openings. To his surprise, he was offered a position as an assistant to the observatory's director, Percival Lowell.
Tombaugh's job at Lowell Observatory was to photograph the night sky in search of the elusive ninth planet, which was believed to exist beyond Neptune. The task was a difficult one, as the planet was too faint to be seen with the naked eye and too distant to be detected by telescopes of the time.
After months of searching, Tombaugh made a breakthrough on February 18, 1930. While examining two photographic plates taken on different nights, he noticed a small speck that had moved slightly between the images. This was the evidence he had been looking for - a new planet beyond Neptune. The planet was named by 11-year-old Venetia Burney, a schoolgirl in Oxford, England. The name was officially adopted in May 1930, a few months after the discovery was announced. The name Pluto was chosen in part because it starts with the letters "PL," the initials of Percival Lowell, the founder of the observatory who had predicted the existence of the planet before his death in 1916.
The discovery of Pluto was initially hailed as a major achievement and the last piece in the puzzle of the solar system. However, as technology advanced and astronomers began to study Pluto more closely, it became clear that it was much smaller than originally thought. In 2006, the International Astronomical Union (IAU) reclassified Pluto as a "dwarf planet," a decision that was met with controversy and debate.
The decision to reclassify Pluto as a dwarf planet was based on several factors, including its size, shape, and orbit. Pluto's orbit is highly elliptical and crosses the orbit of Neptune. It also has a highly tilted and elongated orbit, which makes it different from other planets. Pluto's size is also much smaller than the other planets in our solar system, and it shares its orbit with other objects in the Kuiper Belt.
Despite its reclassification, Pluto remains a fascinating and intriguing object in the solar system. It is the only dwarf planet to have been visited by a spacecraft - NASA's New Horizons mission, which flew by Pluto in 2015 and provided scientists with a wealth of new data and images.