On this eve of the Pluto flyby of the New Horizons spacecraft I could not help but think of how much has changed for the planet since the probe’s launch over nine years ago in January of 2006. Indeed nothing actually changed for Pluto itself, but for the way we define and classify him (her?) and the presumed hundreds of other celestial bodies like it. See, when New Horizons launched, Pluto was still classified as a planet. In August of that same year the International Astronomical Union (IAU) declared Pluto to be a dwarf planet. This was a big letdown to the ninth planet  lovers everywhere.

As the only planet discovered by an American astronomer, Pluto had become an American icon. Even Mickey Mouse’s dog bears the name. And many Americans, as well as some other folks around our planet, were not comfortable with the designation change. One man stood to receive much of the heat for re characterization of the icy Pluto. That man was Neil deGrasse Tyson, and in 2009 he described from his own point of view the path out of planet-hood that Pluto took in his book, The Pluto Files.

Earlier this year Dr. Tyson was going to be doing a lecture here in St. Louis. In anticipation of my attendance, I decided to to pick the book up.

Long before we knew of nine planets in our solar system, we had already settled on eight. In fact, Tyson starts out by pointing to the Adler Planetarium in Chicago was out-of-date the day it opened its doors. Opening only two months after the discovery of Pluto by Clyde W. Tombaugh in February of 1930, Adler had already been designed to showcase eight planets. One can still go there today and see the plaques depicting the eight planets which after 76 years of being out-of-date are finally right with the times.

I think that Tyson was pointing this out to exemplify the cost of changing our view of the universe and our solar system in particular. In reclassifying Pluto, textbooks need to be revised, museums need to be reorganized, and entire generations of people will go on without accepting it because either they do not care enough, they are unwilling to see the nuance as to why, or perhaps because of the culture surrounding our old understanding.

Mickey’s dog was far from the only part of this culture. Upon the discovery of Pluto, this new planet was an budding rock star. In 1932 a laxative known as Pluto Water hit the market. In 1941 a new element who needed a name became known as Plutonium. And of course how can anyone raised in the 80s and 90s forget that My Very Educated Mother Just Served Us Nine Pizzas? If Pluto is no longer a planet, many Plutophiles have pointed out, we have to come up with a new mnemonic. Indeed the culture of Pluto was strong and so demotion was destined to bring about controversy.

Throughout describing the history and science surrounding Pluto, Tyson helps to distinguish it from what we now define as a planet. For example, Pluto is mostly made of ice. Pluto’s moon, Charon, is so large that center of motion is between Pluto and Charon. Every other planet in the solar system has moons whose center of motion lies within the boundaries of the planet. Pluto is so small that it is less than five percent the size of mercury. Pluto also exists in the Kuiper belt along with many smaller ice balls as well as some similarly sized icy objects. Should we start calling the larger of those planets as well? For a little while some people did.

Of course Tyson was not personally or otherwise responsible for Pluto’s fall from grace. The planet had long been on the radar in a large part due to the discovery of Kuiper belt objects that were increasingly closer to Pluto’s size. What put Tyson in the crosshairs of the Plutophiles was mostly exposure due to his involvement of the design of the New York Hayden Planetarium’s Rose Center for Earth and Space. Given the climate of disagreement of how to classify Pluto among relevant scientists at the time and the permanence of the Rose Center which was to be built and opened in 2000, some presentational creativity was going to be required. Instead of an “enumeration of orbs to be memorized” (Tyson, 2009), they presented the solar system as families of objects with similar characteristics. You have the Sun, the rocky terrestrial planets, the asteroid belt, the gas giants, and the Kuiper belt. Pluto lives in the Kuiper belt.

No one really noticed that Pluto was missing from the presentations of the Rose Center until a New York Times article came out almost a year after its opening. The article was titled, “Pluto’s Not A Planet? Only In New York”. This is when the firestorm started for Tyson. In the book several humorous letters are shared from various elementary classrooms begging Dr. Tyson to make Pluto a planet again. This was probably my favorite part of the book. I never cease to be amused by the visceral reaction to those who resist a change that is so obviously needed.

Part of the problem for the IAU was that there hadn’t really been a formal definition of the term planet. Therefore, the task ahead was to formulate that definition which then included them deciding what to do if or when certain celestial bodies did not make the cut. In any event there were no longer going to be nine planets in our solar system. If Pluto made the cut, Pluto’s moon, another Kuiper belt object named Eris, and an asteroid belt object named Ceres would also have become planets. As it turned out. All four of those objects became part of a new class called dwarf planets.

For Tyson, the emails came at a rate of hundreds per day. Articles were written blasting the decision. Even many astronomers were burned by the development. But no amount of passion from the Plutophiles could reverse it. Pluto was now a dwarf planet. When I saw Dr. Tyson’s lecture a couple of months ago, he could not have put his attitude toward it better. In three words he said, “Get over it.”

The Pluto Files is a fascinating read. I hope this week as you are enjoying the new data coming from our favorite little dwarf planet, you might give this book a look.

Kirk Aug

Kirk has conflicting feelings about losing the planet Pluto. He is excited to see whatever thing New Horizons takes pictures of. Follow him on twitter @kirkaug