HowDoWhy

Poor Pluto. Discovered in 1930 by Cylde W. Tombaugh, Pluto was thought to be the missing planet theorized to exist based on inaccurate calculations. It was added as our ninth planet and actually sparked quite a fan following with its popularity, even inspiring the name of a famous Disney character. For 36 years, humble little Pluto quietly orbited our Sun, oblivious to all the fuss it inspired. The enthusiasm gradually waned as more exciting (and accessible) planets grabbed the spotlight.

As discussed in my previous post - What is a planet? - a meeting of the IAU in 2006 finally settled on the definition of a planet. The unfortunate side-effect of that decision was Pluto being downgraded from planet to “Small Solar System Body” or SSSB. This decision was largely driven by the discovery of several new “planets” in a very short period of time. With improving optics and observational techniques, it became clear that it isn’t at all unreasonable to imagine we’ll find dozens of “planets” similar in size to Pluto orbiting in the Kuiper belt or the Oort Cloud beyond. With the assumption that Pluto-like bodies are a dime-a-dozen, the not-entirely-popular decision was made to downgrade Pluto and any similar objects found in the future. This decision was made despite a fairly vocal outcry that diminutive little Pluto be grandfathered in and retain its planet status. Scientists aren’t much for compromise, it seems.

Charon, formerly known as Pluto’s moon, has actually been upgraded to equal footing with the SSSB formerly known as planet. Pluto and Charon are now a binary SSSB pair rather than a Planet and a moon.

If you’re interested in learning more about Pluto, visit Nine Planets and read Dr. Alan Stern’s detailed write-up on our distant little friend who, despite all the fuss it caused, still quietly orbits our star, oblivious to the new hooplah it inspired 36 years after it was first discovered.