COUNTERPOINT Magazine | "It's Okay Pluto, I'm Not a Planet Either"

Pluto's recent fall from grace has garnered a rare degree of attention from pop culture for a science dispute. "To pluto" became a verb meaning to demote or devalue something; the American Dialect Society dubbed it 2006's Word of the Year. Like nearly every other pop culture phenomenon of the last four years, the news about Pluto merited the creation of Facebook groups to cover a range of opinions, including the title of this article, as well as "When I Was Your Age, Pluto Was a Planet," "If Pluto's Not A Planet Than Midgets Aren't Really People" and "If Bush Can Be President, Why Can't Pluto Be a Planet?". The reaction to Pluto's demotion has even spawned its own satire groups: "When I Was Your Age, Pluto Was a Disney Character." Documenting the response on Facebook is all well and good, but how are astronomers taking the change?

I recently went to catch up with my first-year academic advisor, Professor Richard French, Chair of the Wellesley College Astronomy Department. In the same tone in which we in my native northern Jersey would say, "So, about them Yankees," I opened the conversation with, "So, Pluto's not a planet anymore. Is that demoralizing or were you rooting for it?" I expected a smile or maybe even a chuckle in response to this in-joke, appreciation for my awareness of what I assumed was one of the more humorous and trivial topics in his field. I was trying to open with an icebreaker to put us both at ease after a long time apart. You know, levity.

So much for levity. He instantly looked about ten years older, and with the air of a veteran remembering how a fellow soldier had died in his arms said, "Oh God, I was part of that whole mess."

In fact, he took part in the vote about whether to change Pluto's planetary status at that especially acrimonious convention of the International Astronomical Union (IAU) in Prague in August 2006. The decision was so contentious that it will likely be brought back to the table at the IAU's next meeting in Rio de Jainero, Brazil, in 2009. Professor French tells me that demoting Pluto to a dwarf planet was a surprisingly politically loaded decision for something so seemingly esoteric. It was actually considered unpatriotic to revoke Pluto's former appellation because it was discovered in the U.S. and thus is an American institution much like Ellis Island, mom-and-pop corner stores or Chuck E. Cheese's.

To be specific, the existence of a ninth planet in our solar system was predicted by Boston gazillionare Percival Lowell in the early 1900s (though he believed it would be a gas giant). Pluto itself was discovered some time later by a young astronomer named Clyde Tombough who worked at the observatory that Lowell founded in Flagstaff, Arizona. There is a passage in one of my favorite books of all time, A Short History of Nearly Everything by Bill Bryson, which mentions that Lowell is featured in "the famous ditty about Boston being the home of the bean and the cod, where the Lowells spoke only to Cabots, while the Cabots spoke only to God." In fact, the name Pluto was chosen partially because the first two letters are an acronym of Lowell's name (PL for Percival Lowell), and the symbol for Pluto is a stylized monogram of his initials.

Lowell was otherwise known for his conviction that water canals existed on Mars, engineered by Martians in order to carry water from the polar regions to the dry equator. The Lowell Observatory renewed the search of the elusive ninth planet, dubbed Planet X by Lowell, partly to detract attention from this embarrassing pet theory of its benefactor. Tombough finally spotted Planet X in 1930. To quote author Bill Bryson again: "This was the first American-discovered planet, and no one was going to be distracted by the thought that it was really just a distant icy dot." In fact, there are at least seven moons in our solar system that are bigger than Pluto, including the local one we spent so much money to beat the Russians to. Bryson states: "It is very tiny; just one-quarter of one percent as massive as the Earth. If you set it down on top of the United States, it would not quite cover half of the [...] forty-eight [mainland] states."

It is not even the biggest dwarf planet in the solar system; this distinction goes to Eris, an object 27% more massive, discovered in 2005, which orbits the sun from way out in the Kupier belt. The discovery of Eris, which NASA initially hailed as the solar system's tenth planet, reignited the already heated debate about what constitutes a planet. In 2003, the International Astronomical Union had decided, for the very first time in the thousands of years that humans have studied the sky, to come up with an official definition: a planet is an object which orbits a star and has enough gravity to hold itself in a roughly round shape. This definition not only labeled Pluto as a planet, but also meant that our solar system contained no fewer than twelve planets. The twelve consisted of the famous nine plus Eris, Ceres (now considered a large asteroid) and Charon (now considered a moon of Pluto). Three years later, in the same conference which shell shocked my advisor, the IAU added a crucial third criterion which brought us back down to eight planets. Ladies and gentlemen, the official planetary definition as of this writing in January 2008 according to the IAU's website: "A planet is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit [i.e. it is the most gravitationally dominant object in its path or orbital zone and has either knocked away smaller objects or pulled them in to become its satellites]."

It is the last criterion that Pluto, Eris, Ceres and Charon all fail. Mass equals gravitational attraction, and none of these objects is massive enough compared to the rest of the matter in its orbit to be considered gravitationally dominant. According to Steven Soter's 2007 Scientific American article "What is a Planet?", the mass of Pluto is only 0.07 times the mass of the other objects in its orbit. By contrast, Earth's mass is 1.7 million times the remaining mass in its own orbit.

There is disagreement within the scientific community about the validity of the 2006 definition. Some complain that "clearing the neighborhood" is not precise enough to be meaningful. Others discount the decision because only about 5% of professional astronomers in the world voted at the convention in Prague, so it might not represent the views of the profession as a whole (to this astronomer Marla Geha retorted, "[A]stronomy is a diverse field with many different areas of specialization. The majority of astronomers don't work on planets. It would be like questioning the results of a Republican primary because the Democrats failed to vote.") Still, others rightly point out that because of the phrase "orbit around the Sun," there is currently no such thing as an extra-solar planet. The 2003 incarnation of this definition had identical wording for the first two criteria except that it said "orbit around a star." The change is puzzling.

There is enough legitimate disquiet to warrant a scientific reevaluation of the issue at the next IAU convention next year. However, if the sentiment of Internet forums is any indication, most people's reluctance to give up Pluto's planetary status seems to be based not on science but on stubbornness and nostalgia. Quoth some of the aforementioned Facebook groups:

"How dare these scientists ruin our childhood? We grew up with it, it's staying with us."

"As of August 24, 2006, Pluto was demoted to a 'Dwarf' Planet. We feel that this is derogatory and Pluto has a right to be a planet. It is unjust and unfair for scientists to rescind a title that was granted in 1930."

"Everyone knows there are 9 planets in our solar system, and pluto [sic] is one of them. In fact, its [sic] the best one. None of this bullshit about how it used to be a planet, or about what the moron astronomers think, anyone who joins this group knows that this solar system is a family, and we dont [sic] just go around throwing out valued members of our family like that."

Not that I don't enjoy some of pop culture's humorous irrationality, but this logic worries me. It borders on the same "it MUST be true because I really, reaaaally believe it and my mom and dad do, too" line of thought that causes 51% of Americans to deny that evolution is real (according to a 2005 poll by CBS News). Perhaps we should all chill out, grow up, stop assigning so much sentimental value to the outcome, and let the astronomers decide which definition is most scientifically sound.

Samantha Lowe WC '10 (slowe[at]wellesley[dot]edu) prefers Mickey Mouse.

February 2008
Volume 31/Issue 5

"It's Okay Pluto, I'm Not a Planet Either"

Astronomers still question Pluto's demotion

{by samantha lowe wc '10}

February 2008Volume 31/Issue 5

"It's Okay Pluto, I'm Not a Planet Either"

Astronomers still question Pluto's demotion

{by samantha lowe wc '10}

February 2008
Volume 31/Issue 5