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The Short and Sad History of Pluto, the Ex-Planet

The Short and Sad History of Pluto, the Ex-Planet

By Swapna Krishna

Pluto's kicked the bucket. It's shuffled off its mortal coil, run down the curtain, and joined the bleeding choir invisible. Pluto IS AN EX-PLANET.

If you've never seen Monty Python (and if not, you're missing out!), then you won't understand the reference, but you'll get the point: Pluto was voted an ex-planet in 2006. While this may seem unfair to poor little Pluto, you have to take some facts into consideration. It doesn't look like a planet (its surface is composed of roughly 98% nitrogen ice), it doesn't act like a planet (remember that elliptical orbit you learned about in grade school?), and to be quite frank, it's... well... small. Way too small to really be considered a planet.

But our little-engine-that-could dwarf planet does have one thing other big boy planets have: moons. Last week, the Hubble Space Telescope discovered a fifth moon orbiting Pluto. Called P5, this little moon is no more than 25 kilometers across. This celebrated news has inspired us to give a brief history of the sad once-planet known as Pluto.

  • Pluto was the only planet discovered by an American. Though Pluto's existence was long-predicted, it was Clyde Tombaugh, a 23-year-old from Kansas who first discovered the wayward little dwarf in 1930.
  • Pluto was named by an eleven-year-old from England in the same year. The name was suggested because it's the Roman name of the god of the underworld, but we now happily associate it with Mickey's pet pooch.
  • They thought Pluto was much bigger than it actually was. Throughout history, theories on Pluto's size have been revised downward over and over again. Its actual size? About one-sixth of the mass of our beloved moon.
  • Pluto's first moon, Charon, was discovered in 1978. Over the years, it's become clear that Pluto-Charon is a binary system; Charon doesn't revolve around Pluto, but they revolve around each other, with their center of gravity being a fixed point in space.
  • The controversy about Pluto's planet status has been going on for years, and it came from a variety of sources. One of the main sources of controversy was the Hayden Planetarium which, under the guidance of astrophysicist Neil deGrasse Tyson, reopened after a renovation in 2000 with only eight planets labeled. Pluto was labeled a Kuiper Belt object.
  • The firestorm continued, with Tyson at its helm. He responded to the controversy, affirming his belief that Pluto should not be categorized as a planet. Other experts weighed in, and upon the discovery of multiple objects in the Kuiper Belt that approached Pluto's size (chronicled in Mike Brown's How I Killed Pluto and Why it Had it Coming), it was clear a new solution to the Pluto problem was needed.
  • On September 13, 2006, the International Astronomical Union declared that Pluto was not a planet because it has not "cleared the neighborhood around its orbit", meaning that a planet must have enough mass to ensure that it is the dominant gravitational point in its orbit, with the only other objects in its orbit being its satellites.

And there you have it, the sad history of the ex-planet Pluto. It's now considered a dwarf planet, which, let's face it, is most definitely second-class status, a consolation prize because Pluto just couldn't cut it with the rest of the planets.

What's your favorite planet?

Tags: outer space, life, pluto, planets, solar system

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About the Author
Swapna Krishna

Swapna is a Washington, DC-based freelance editor who loves all things space and sci fi. You can find her book reviews at S. Krishna’s Books (http://www.skrishnasbooks.com) and on Twitter at @skrishna.

Wanna contact a writer or editor? Email contribute@sparknotes.com.