The Space Reviewin association with SpaceNews

IAU GA vote
Astronomers at the IAU meeting last month cast their votes on a resolution defining the term “planet”. (credit: IAU/Lars Holm Nielsen)

Inside the planet definition process

<< page 1: an alternative definition

Reaction and criticism

The reaction to the turnaround in Prague, going from nine to twelve to suddenly only eight planets, had an enormous echo in the world’s media and continues to do so even two weeks on (See “Demote Pluto, or demote ‘planet’?”, The Space Review, August 28, 2006). Commentaries were split between “Pity Poor Pluto!” obituaries without any real arguments why it should have stayed a planet and those recognizing that it hadn’t deserved that special status in the first place. People dealing with the solar system in various ways, especially as educators, adapted right away, according to many news reports, and the “Sun and eight planets” seemed to take hold surprisingly quickly. The most vicious attacks against the IAU decision came from a number of (exclusively American) planetologists, who mostly attacked certain details of the dramatic events that had taken place in Prague, of which most had only secondhand and sometimes distorted knowledge. Some 300 (again, practically all based in the US) also signed a petition that was circulated by personal e-mail and didn’t include any factual arguments against resolution 5a but simply read: “We, as planetary scientists and astronomers, do not agree with the IAU’s definition of a planet nor will we use it. A better definition is needed.” When contacted by The Space Review, the initiators of the petition and some of the signatories explained their motives (or made them known elsewhere).

The reaction to the turnaround in Prague, going from nine to twelve to suddenly only eight planets, had an enormous echo in the world’s media and continues to do so even two weeks on.

Many were unhappy with the wording of the key criterion in resolution 5a, about a planet having “cleared” its neighborhood, and this seems to be rather sloppy indeed. But, as UB313 discoverer Mike Brown explains, “the concept is more important than a lawyerly reading of the definition” as voted on, and “the difference between the eight planets and everything else known in the solar system is so huge that even a definition with a lot of wiggle room will not make any difference… The precise wording of the definition might need to be fixed still, but the hugely important astronomical concept of what now separates planets from non-planets should be clear to all.” It did not help that the new resolutions did not come with the same detailed documentation as the original one. And if the EC would have gone with the alternative draft presented in the August 18 debate, making a planet simply “by far the largest object in its local population”, a lot of the objections—valid but often voiced in an insulting language—might have been avoided.

It was also questioned in some (again, mostly American) circles whether those 420 astronomers casting their vote in Prague—less than 5% of the current IAU membership and perhaps 1% of the world’s working astronomers—are entitled at all to make serious decisions for the world’s astronomical community. This is hard to determine and actually goes straight to the core of what one considers a democratic process. The voting astronomers in Prague had been exposed to intense arguments from all camps and often participated themselves in deep debates, which led to significant changes in the resolution’s content. Moreover, at least some of them had contacted their constituencies in their home countries (or received input from their colleagues by e-mail), to make sure they were speaking for more people than just themselves: the objection that the debate at the GA was “insular” and not representative is simply untrue. Finally, the results on resolutions 5a and 5b truly represent a clear majority, almost consensus, view among all the GA participants, as far as this and other observers can tell.

The term “dwarf planet” as such, whether one accepts the new categorization of the solar system or not, also causes opposition: “dwarf” could be read as an adjective and thus those bodies would be planets after all—just small ones, it is claimed—in spite of the IAU stating exactly the opposite and the strong rejection of resolution 5b. Perhaps only experts in the English language can judge that, but the author, a non-native speaker, cannot but wonder why, if “dwarf planet” is so problematic, the long-established term “minor planet” should not cause the same misunderstanding. According to my dictionary, both “minor” and “dwarf” can be used as or are adjectives, actually meaning about the same. Some alternatives to “dwarf planet” were thrown around in Prague at the last minute, e.g. “planetino”, and in the final debate there was even a call to the EC to invent a new word for these bodies that does not exist yet in the English language. (The Executive declined.)

The tumultuous events of August 2006 are as much a lesson in sociology as in astronomy.

The main intention of the anti-IAU petition, besides generating press coverage for its angry authors (it did), was to initiate a conference in mid-2007 to discuss the planet definition issue all over again and to form what the initiators believe will be a true(r) consensus view which would then be presented to the world. The procedural flaws in the handling of the whole affair by the IAU EC are rather obvious, especially the secrecy prior to August 16 that backfired by compressing the whole complex debate into a window of eight days, and the overly hasty drafting of resolution 5a that had to follow. Nonetheless, during the debates on August 18 and later, all the key arguments for the various possible planet definitions were presented already, including some proposals that are again very different (such as using the absolute brightness as a criterion or whether a substantial atmosphere is present—bye bye, Mercury, hello Titan). Then, a cross-section of the world’s astronomers—which a dedicated anti-IAU conference would hardly bring together in such a way—held a vote, with a clear result which in turn is already gaining some acceptance because the “concept”, to use Mike Brown’s words, is sound. Even though it involves the “trauma” of losing a planet that was popular for sometimes very strange (read: canine) reasons. On September 7 the IAU’s Minor Planet Center formally assigned to Pluto the minor planet number 134,340 as so far no decision has been made to open a new catalog for “dwarf planets”.

The tumultuous events of August 2006 are as much a lesson in sociology as in astronomy. Discussing what happened with the general public, you notice that the more they learn about the arguments behind the decision, the more they understand and accept it. This adds to the argument that a vote by a fraction of the world’s astronomers after a week of intense arguments might be a better way to determine where to go than aggressively promoted e-mail campaigns. Interestingly one of the signatories of the anti-IAU petition told The Space Review that his “decision was made fairly lightly, I must admit” and that “few of my colleagues or I feel particularly strongly about this. It’s a tempest in a teapot, from my point of view.” Another signatory told The Space Review he was simply angry that he as an IAU member —but too sick to travel—could not cast his vote remotely. Actually the possibility for electronic voting may be introduced at the next IAU GA in 2009 (it would involve changes in bylaws only GAs can make), but the disadvantage would be, of course, that those not present would not be exposed so directly to the arguments and debates: a major problem with e-democracy.

The nasty and plainly bizarre sides of the whole planet definition affair aside, a lot of good seems to come out of it already. Hardly ever in past decades have so many people thought so much about the ways our solar system works. Science progresses, and sometimes our view of things has to adapt: Schools in particular could pick up this far deeper meaning of the “demotion of Pluto”, and, according to numerous newspaper stories, teachers and students alike are not letting this opportunity pass indeed! In one class in Pasadena, California, students had held informed debates on Pluto’s planethood for five years, with the usual outcome a clear vote against it being a real planet. At one point a class had even written to the IAU to report the result of their deliberations. And while the Executive didn’t follow suit, the Prague GA now did exactly that: Can you imagine how proud these students must be now? The solar system is exactly the same as it was before August 24, but the knowledge about its structure and multitude of fascinating inhabitants in wide circles has grown substantially since. “The fact that the public cares,” said The Virginian-Pilot in an editorial five days later, “makes astronomy relevant in a way it often isn’t. You’d need a mighty powerful telescope to find the downside in that.”