The Case for Demoting Pluto

Since its discovery by Clyde Tombaugh (and naming by Venetia Phair) in 1930, Pluto, a mere ball of ice and rock beyond Neptune, has been regarded as the ninth planet of our solar system. Only in recent years, with the discovery of other small, icy, spherical bodies in the outer reaches of our planetary neighborhood, have we come to realize that Pluto may only be the first of several similar objects. This has raised the question as to whether Pluto is rightly classified as a "planet," when it is only one of what could be hundreds or thousands of similar "planets."

The World is a Circle

In response to this planetary quandary, the International Astronomical Union has proposed alternative options for astronomical nomenclature with regard to the classification of "planets." Chief among these options is the establishment of the following criteria: a "planet" must be orbiting a star (while not being a star), and it must be massive enough to form into a reasonably spherical shape.* Hence Pluto would remain a planet, but this reclassification would effectively introduce other solar system objects to the definition of "planet" -- objects like Ceres, Quaoar, Sedna, 2003 UB313, and, yes, Pluto, plus its own moon, Charon. These would be differentiated from the eight "classical planets" by the name "Pluton," a subclass of "planets" similar to Pluto -- rocky, small, mostly spherical, with eccentric orbits.

* Update: The new IAU resolution defines a "planet" as a body orbiting the sun which is not a satellite, is massive enough to become spherical, and "has cleared the neighborhood around its orbit"; a "dwarf planet" as a smaller sun-orbiting spherical body which "has not cleared the neighborhood around its orbit"; and the leftovers like asteroids and comets, called "Small Solar System Bodies."

And Nobody Knows Where the Circle Ends

Recent discoveries should cause us to rethink Pluto's "planet" status, as its newly found siblings would more correctly be classified as "planetoids" and/or "Kuiper Belt Objects," but sentimentality over Pluto's stature in human history has clouded popular judgment over these concerns, causing many to twist what should be a simple recategorization into a bureacratic mess of special-case definitions which serve only to confuse the already muddled layman's understanding of astronomy.

And Just Because You Think You're Small

The Pluto-Charon system is too small and common in the outer solar system to be rightly categorized as a planet, and should be removed from the repertoire. Otherwise the panoply of planets in our solar system -- and in other planetary systems -- would grow at an unmanageably rapid pace as we discover more and more "Plutons," and our astronomy textbooks would become hopelessly out of date with every new discovery. Realistically, categorization of solar system bodies would be far easier and more sensible if we were to limit types of bodies to (1) terrestrial planets, (2) gas giant planets, and (3) other leftover debris from the formation of the solar system, such as comets, asteroids, planetoids -- and Pluto.

That Doesn't Mean You're Small at All

There is, at least, enough flexing room in this categorization to grant a concession to those still desirous that Pluto should enjoy some remnant of its grand 20th Century background as the sometime Ninth planet of Sol: we can keep the name "Pluton" as a category for similar spherical planetoids drifting through the outer solar system. This establishes Pluto's status as the first of such objects discovered, and is more than enough of a tribute to its human history.

Update: The proposed name "Pluton" has been discarded by the IAU in favor of "dwarf planet." This seems to be a decent compromise classification for massive spherical KBOs like Pluto. We approve.

To Someone Else You Are Big

Our enemies are gathered, aiming to overthrow the Demotion Initiative and let illogical, anthropocentric nostalgia dictate how we view the concept of "planet," all for the sake of their misguided love for Pluto. We at urge the members of the IAU to do the right thing, and Demote Pluto Now.

See the Frequently Asked Questions for answers to common concerns.