Pluto and the priesthood of science

And then I wrote… In place of the weekly columns originally published in The Tablet I am running odd articles that I have written and published over the years. This one came from a blog I used to write, and it covers a topic of occasional interest even today. I first posted it in 2009.

I suspect I am letting myself in for it by posting this, but someone has to say it…

Before the IAU meeting this past month in Rio [this was written in 2009; it was the previous IAU General Assembly in 2006 that had redefined the status of Pluto], I received several emails from impassioned folks offering petitions to try to get Pluto “reinstated” as a planet. Needless to say, that was the farthest from anyone’s mind at the IAU. As these petitions reveal a deep misunderstanding of what science is in general, I thought I would pass on a few comments here. 

I have written at length about the whole Pluto controversy elsewhere (see “What happened to Pluto?” in The Physics Teacher, 45, 14-19 which was expanded upon in chapter 2 of my 2014 book with Paul Mueller Would You Baptize an Extraterrestrial?) and I don’t want to repeat any of that information here.

[2020 comment, not in the original blog post… after trying to explain the Pluto decision over and over at great length, to no avail, I have discovered that the quickest way to end the argument is to ask, “Why do you insist that being a planet is somehow better than being any other kind of object? Aren’t you being guilty of rampant Planet-ism?”]

Instead, I want to examine some of the hidden incorrect assumptions that the petition-forwarders have about who the IAU is, what we do, and why we do it.

First misunderstanding: They seem to think that science is about “facts”. The petitions argue about the “fact” of Pluto’s status, i.e. where it sits in a list in a textbook. But the science of astronomy is not at all about lists or textbook facts. Those lists are what precocious 8 year old children love to memorize; that is no longer what is of interest to the rest of us. As astronomers, we want to understand what’s in the universe, and how it got to be the way it is today. In order to do this work, we must work in international communities and we must have a common language to describe the things we’re looking at. That’s why the IAU exists: to facilitate our work.

For example, a few years ago – just before the 2006 IAU reclassification – I was curious…

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… if the spin rates and light curves of distant objects in the solar system could be reliably connected to their densities and internal structures. (It turns out to be more complicated than “yes it works” or “no it doesn’t,” which is precisely what I was trying to work out.) As part of that work, I needed to consult tables – yes, lists of “facts” – that contained the data I needed for the objects I needed. But notice, it wasn’t the facts themselves I was working on – they were already known – but how those facts could be used to tell me about what was going on in the solar system.

Clearly in doing this work I had to consider a whole range of objects, including the largest of the TNOs. At that time, however, neither Pluto nor several of the other Pluto-sized objects were in those tables since it wasn’t clear what status they had. When there was only one Pluto, that was simple enough; I could look it up separately. But in a rapidly changing field where new such objects were being found all the time, I had no idea if I had a complete set of all of them, including some of the most important examples of the class of object I was looking for.

Second misunderstanding: They seem to assume that the IAU is somehow an authority on “what is a planet” similar to the authority of a government or a church. If that were true, then understandably its decisions would matter to everyone; and so everyone involved ought to have a say about those decisions. Certainly that is the way the IAU decision was described in the popular press. But, operatively, this is just not true. The IAU has no desire to define “facts” for the rest of the world. It has neither the authority to do so, nor the power to enforce any such decisions.

All the IAU decided back in 2006 was to figure out which of two different sets of committees would be responsible for handling the nomenclature and the listing of data on orbits and other physical properties. Up to that time, Pluto’s data were not included in the listings of the Minor Planet Center (MPC). After that decision, Pluto and the other bodies fitting the Dwarf Planet definition, some of which are larger than Pluto, were each given a minor planet number and each body’s data were listed among all the other similar bodies in the MPC database. By all accounts, and as the subsequent three years’ practice has shown, this makes perfect sense. The kind of data listed in this database is precisely what I needed, for example, in the task I described above.

In a similar way, after 2006 the task of approving a common name to be used for the other newly discovered dwarf planets was regularized, to be handled jointly by both the committee in charge of planet and moon names (the Working Group of Planetary System Nomenclature, WGPSN) and the committee in charge of minor planet names (the Committee on Small Body Nomenclature, CSBN). 

(Why are there two different nomenclature committees? Because the constraints and needs of the two different kinds of bodies are very different. The WGPSN has to understand both its complex naming conventions – which planets have which type of names – and the differences between different kinds of geological features which are getting named. Small bodies, on the other hand, don’t have to worry about that kind of geology; they have a different set of constraints – what naming conventions are followed for bodies based on their orbital characteristics, for example – that are very different from the planetary group. Incidentally, when there are geological features to be named on small bodies, it is the WGPSN that handles that, not the CSBN.)

In other words, the 2006 IAU decision about Pluto was a purely internal administrative decision, about what kind of classification was most practical and most useful for the astronomers using the IAU databases, and who would be in charge of maintaining those databases.

And so there are several reasons why the well-meaning “petitions” about Pluto miss the mark. 

They seem to think that Pluto’s status is a “fact” of great importance. Worse, they imply that these “facts” can be decided by popular vote. 

Likewise, what these petitioners are implying (without realizing it) is that even though they don’t actually use our data on a daily basis like we do, nonetheless they somehow have the right to tell us how to classify our data, based not on our practical needs but on their emotional desires.

And they put way too much authority on the shoulders of the IAU, treating us as if we were some sort of College of Cardinals. It really bothers me when people want to turn being a scientist into a kind of “priesthood” with an authority that we neither have nor desire to have. It falsifies both what it means to be a priest and what it means to be a scientist. And I find that very upsetting… maybe because I work at the Vatican Observatory, where I see real priests, and real scientists, every day!