Kayla Randall
| Digital Editor, Museums
A 24-year-old observatory assistant from the Midwest discovered Pluto. Clyde Tombaugh, born in 1906 in Streator, Illinois, grew up fascinated with the solar system. A self-taught astronomer, he built his own telescopes to observe Mars and Jupiter.
Tombaugh wrote a letter to the Lowell Observatory in Flagstaff, Arizona, asking for a professional opinion on his celestial drawings, and the staff ended up offering him a job as an assistant, searching for a hypothesized, elusive ninth planet. On February 18, 1930, at the observatory, he was studying photographic glass-plate images he had taken with a telescope. Using a blink comparator, he examined two plates captured days apart, and noticed a tiny dot featured on both of them but in different locations. The dot had moved.
That dot was the small and icy Pluto. Tombaugh had found what he and observatory leadership were seeking.
âIt took the right person with the right amount of focus, because it was a needle in a haystack looking at dotsâa dot that moved against the background of hundreds of thousands of dots,â says Kevin Schindler, the longtime historian and public information officer at the Lowell Observatory.
After more studying, on March 13, 1930, the observatory team publicly announced the discovery of the planet. That day would have been the 75th birthday of astronomer Percival Lowell, who had set up the eponymous observatory in 1894.
Lowell had suspected that a ninth planet, which he referred to as Planet X, was out there, beyond Neptune. In 1905, he began to formally search for it. But Lowell died in 1916, after spending the last 11 years of his life, off and on, looking for Planet X. Though he never got to witness Plutoâs discovery, the finding at his own observatory was the realization of his dream.
âThey ended up calling it Pluto, because in mythology, Pluto was the god of the underworld,â Schindler says, âand this made sense, because Pluto was so far away.â
The legacies of Lowell and Tombaugh continue in the Flagstaff community to this day. Every February, the Lowell Observatory hosts its I Heart Pluto Festival. âIt draws a lot of people, and itâs really a lot of fun,â says Schindler. Observatory staff members are already gearing up for Plutoâs centennial in 2030.
âFlagstaff is Plutotown, USA,â he says.
Now, 20 years after the International Astronomical Union (IAU) voted, on August 24, 2006, to remove Pluto from its ninth-planet status and redesignate it as a dwarf planet, the enthusiasm for the icy body endures. In fact, that decision sparked even more fascination with Pluto, says Schindler.
âIt keeps people interested,â he says. âIt keeps people really fired up about it.â
Following the 2005 discovery of Eris, a distant dwarf planet similar in size to Pluto but with more mass, the IAU considered adding more planets to the solar systemâs total. Eris and other recent discoveries âhave rightfully called into question whether or not they should be considered as new âplanets,ââ Ron Ekers, then-president of the IAU, said in 2006. As the âarbiter of planetary and satellite nomenclature,â the IAU had been working on a new formal definition of the term âplanetâ for about two years.
One proposal discussed at the unionâs general assembly in August 2006 would have established 12 planets by adding Ceres, Charon (Plutoâs largest moon) and Eris to their ranks. That proposal was eventually rejected, in favor of reducing the number of planets to eightâand excluding Pluto.
Instead of the solar systemâs ninth planet, Pluto was reclassified as a âdwarf planet,â separate from the rest. âIt was agreed that âplanetsâ and âdwarf planetsâ are two distinct classes of objects,â the IAU noted at the time.