The History of Pluto
PLUTO IS DISCOVERED
1934
American astronomer Percival Lowell first caught hints of Pluto's existence in 1905 from odd deviations he observed in the orbits of Neptune and Uranus, suggesting that another world's gravity was tugging at them from beyond. He predicted Pluto's location in 1915, but died without finding it. Its discovery came in 1930 from Clyde Tombaugh at the Lowell Observatory (Flagstaff, AZ), based on predictions from Lowell and other astronomers.
KUIPER BELT BODIES
Early 1990s
Astronomers began to discover a variety of objects beyond Pluto, in what is known as the "Kuiper belt" to most Americans, or the "Edgeworth-Kuiper belt" to most Europeans. Objects given names like Sedna, Orcus, and Quaoar began popping up, all slightly smaller than Pluto.
A 10th PLANET?
2003
The situation was brought to a head in 2003 when Caltech astronomer Michael Brown discovered an object larger than Pluto, designated 2003 UB313. Was it the 10th planet, or was Pluto not a planet? And since many more similar objects are now known to exist in our solar system beyond Pluto, with more sure to be discovered, what is their status? The IAU General Assembly meets only every three years; thus these questions were to be brought up for a vote in Prague in 2006.
THE DEFINITION A PLANET
2006
The "Planet Definition" Resolution was put to the 2006 IAU General Assembly. The outcome decided the defintion of what objects in the Solar System should be classified as "Planets." Pluto looses its status as a Planet retuning the total number of "Planets" in our solar system to nine.
REGAINING OF PLANETSHIP
2015
IAU General Assembly met once again this year and re-visited the Pluto's status as a body in our solar system. NASA's New Horizons satellite witnessed an asteroid collide with Pluto in 2011, adding to its size significantly. The Assembly concluded that Pluto now officially meets the definition of the planet, despite still being small in comparison to other solar system bodies.