Pluto At 80

Clyde Tombaugh, a Kansas farmboy with a fascination for astronomy, discovered Pluto 80 years ago today while working at Lowell Observatory outside Flagstaff, Arizona. Tombaugh was searching for Planet X. Astronomers thought there was an as yet undiscovered planet gravitationally tugging on Neptune, creating discrepancies in Neptune's orbit the astronomers found. In fact, in later years after more precise data was available, astronomers determined there were no discrepancies, and Planet X was not needed. The discovery of Pluto, therefore, is an example of those odd twists and turns that litter the history of science.

For decades after its discovery, Pluto was classified as a planet. That's what Tombaugh was looking for, after all. Now, however, exactly how to classify Pluto is unclear. Is it a planet, or a dwarf planet? A Kuiper Belt Object? Maybe a huge comet head? Whatever it is, NASA has a probe on its way to a flyby of Pluto and its companion, Charon, in 2015. If all goes well, that mission will tell us more about Pluto than we've learned in the past 80 years.