The sun is the sun. The moon is the moon. And the Earth is the Earth. But Pluto? Let’s just say things have gone round and round as to whether it’s a planet or not, leaving this celestial body with an identity crisis not of its own making.
Dark days for Pluto
On August 24, 2006, researchers at the International Astronomical Union (IAU) voted to reclassify Pluto and change its status from a planet to a dwarf planet. Many in the scientific community viewed the new designation as a demotion, while the public reacted with outrage and wondered how the solar system could go from nine planets to eight, seemingly in the blink of an eye. Truth be told, Pluto’s change in status was a long time in the making.
Shining a light on an oddball ‘planet’
Pluto was first spotted in 1930 by astronomer Clyde Tombaugh at Arizona’s Lowell Observatory. But in 1992, astronomers at the University of Hawaii observatory in Mauna Kea discovered a small, icy celestial body that was just a bit farther away than the orbit of Neptune. The object, named Kuiper Belt Object 1992 QBI, increased speculation that Pluto was one of many planet-like objects in the Kuiper Belt.
In 2003, Pluto came under the microscope (or should we say telescope) even more when Mike Brown, a California Institute of Technology professor, discovered Eris. He determined that this dwarf planet had slightly more mass than Pluto, and astronomers began to suspect that additional could-be planets might be floating around in space. Rather than give planet status to Eris, the IAU reclassified Pluto.
Things got worse for Pluto in 2006, when the IAU redefined exactly what it means to be a planet. According to the Union’s definition, a planet must be a celestial body that orbits the sun, is round or nearly round, and “clears the neighborhood” around its orbit. Alas, Pluto failed on the third account because its orbit overlaps with Neptune. As a result, the IAU reclassified Pluto as a dwarf planet, also calling it a “Trans-Neptunian Object,” which sounds like something straight out of a bad science fiction movie.
There’s room—and space—for debate
In 2015, NASA’s New Horizons Program flew past Pluto to take a closer look and measure the dwarf planet; results revealed that Pluto is larger and more complex than scientists previously thought. Alan Stern, planetary scientist and the principal investigator for the New Horizons spacecraft, disagrees with the IAU’s demotion of Pluto, as do other noted scientists, including Philip Metzger of the University of Central Florida’s Space Institute. “It’s a sloppy definition,” says Metzger. “[The IAU] didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.”
So Pluto continues to be defined as a dwarf planet denied status as a ‘real’ planet. The debate goes on, the calculations and conferences continue. But whatever changes come, or have already been made, many people still believe in planet Pluto, and love it to the moon and back.