This Week in Illinois History: Clyde Tombaugh discovers Pluto (February 18, 1930)
On February 18, 1930, Clyde Tombaugh of Streator, Illinois, discovered our solar system’s most famous dwarf planet, Pluto. Pluto was the first planet discovered in the 20th century, and the only planet discovered by an American.
Clyde Tombaugh was born to farmers in Streator, Illinois, on February 4, 1906. When he was 16, his family moved to Kansas. At 20, he built the first of many homemade telescopes, cobbled together with spare parts from old farm equipment. He sent drawings of his observations to Lowell Observatory at Flagstaff, Arizona. When he was 23, the observatory hired him.
Lowell Observatory was founded by Percival Lowell, a mathematician and astronomer who believed there was a ninth planet, Planet X, hiding beyond Neptune. He spent the last decade of his life searching for it. He died before Tombaugh’s arrival at the observatory, but Tombaugh took up his quest.
Tombaugh photographed the night sky and compared images to search for moving objects. He confirmed his discovery of a new planet on February 18, 1930. He had been at the observatory less than a year.
Tombaugh’s discovery was a media sensation. Thousands of people mailed in name suggestions for the new planet. An 11-year-old English girl, Venetia Burney, submitted the name Pluto. She thought it appropriate because Pluto was the Greek god of the underworld, a dark, cold place. Astronomers agreed, in part because the first two letters of Pluto are also the initials of Percival Lowell.
Pluto’s reign as our tiniest planet ended in 2006 when the International Astronomical Union (IAU) downgraded it to a dwarf planet, one of many in our solar system’s outer regions. In 2008, the IAU designated Pluto the first of a new class of dwarf planets that orbit the sun from beyond Neptune, plutoids.
In 2015, the New Horizons space probe became the first spacecraft to visit Pluto. It carried some of Clyde Tombaugh’s ashes onboard. During its brief flyby, New Horizons discovered the now-famous heart-shaped region on Pluto’s surface. That heart is now known as the Tombaugh Regio. It is included on a metal sculpture of Pluto that stands in Tombaugh’s hometown of Streator.