Tuesday, August 25, 2009

More thoughts on Pluto and the scientific method

While ruminating on my post on Pluto and the definition of planets yesterday, I thought of a couple other points on the topic that I wanted to make, though not necessarily related.

1. The story of the status of Pluto is a great illustration of the scientific method. The discussion of the discovery of Pluto, the much later discovery of the Kuiper Belt, and Pluto's subsequent demotion is (with one big exception I'll get to in a couple of paragraphs) an excellent illustration of the way that science actually works. When new data comes to light, we should never be afraid to re-examine even the most dear of scientific ideas. No matter how much we love Pluto (and it's okay to love Pluto, to study Pluto, to spend multiple careers working on Pluto, and to revere Clyde Tombaugh and the amazing amount of work he did to discover Pluto), we have to be willing to reconsider its status. To say, "Nope, it's a planet, end of story" or to say, "Nope, it's not a planet, end of story" is to be unscientific.

Further, science rarely gives us clear-cut answers, especially in the short term. Different teams of excellent scientists can examine the same evidence and come to different conclusions. Only through further study and analysis and debate can the deeper, underlying truths of science be brought out. The discussion of what Pluto is continues (though not always in the public eye), and the vast majority of scientists involved, deep down inside want to know the truth as to what is going on. If you want to learn how science really progresses, keep watching the unfolding saga of Pluto. In the end, the truth will be discovered. It just takes time and lots of work.

2. The International Astronomical Union's demotion of Pluto was far more a decision to solve a bureaucratic nightmare than a decision on the underlying science. Three years ago, the International Astronomical Union found itself with a problem. The IAU has, by consensus of the astronomical community, the final say in the naming of objects. And the IAU has devised specific rules for how to name objects, from planets to moons to asteroids. The rules differ greatly -- planets are named after Roman gods, moons of planets have restrictions also based on mythology, but asteroids ("minor planets") can have many other names, such as the asteroid Misterrogers.

With the discovery of Kuiper Belt objects larger than Pluto, the IAU needed to decide what set of rules the naming conventions should follow. What if someone found a Mars-sized Kuiper Belt Object and wanted to name it Bartsimpson? And which committee in the IAU would get to choose the name? Would the discoverer get a say in the name?

So the IAU decided to create the classification of "dwarf planet" to include all the smaller things that were generally round in shape (the biggest asteroids and Kuiper Belt objects), but were not moons and were not one of the classical planets. This designation allowed the IAU to come up with new naming rules, and everyone could be happy.

This turned into a disaster. What should have been simply a rule on how to name bigger round things turned into a vote on what constitutes a planet. And, as I pointed out yesterday, there are many ways of drawing lines, none of which seems inherently obvious. And this definition went through revisions, and astronomers voted on it. Yet this is not how science works. Scientific truths and laws are not decided by vote. The laws of nature are what they are, and it is our job as scientists to figure out what those laws are over time. This can take years, decades, or even centuries, yet the IAU definition was debated, altered, and approved in a couple of weeks.

I think the IAU should probably just have said something like, "We're making a new class of objects for the purposes of naming conventions. Objects orbiting the sun and large enough to be made round by their own gravity shall be named after mythological gods, and not just Greco-Roman gods, and Committee X has the right to decide how such names are to be selected." That would have solved the naming crisis yet allowed the scientific community to continue to debate exactly what makes a planet, and whether there is a fundamental physical difference between different types of rocky bodies.

Alas, this isn't what happened. They shoulda asked me.

3. What should the role of public opinion and historical precedence be, if any? I'm not going to do much more than open this can of worms, but to what extent can or should public opinion matter? After all, even if 100% of the world's people felt that the moon was made out of green cheese, the moon wouldn't magically transform into a giant Limburger; it would stay a round body made of metal and rock. And if 95% of Americans wrote letters to Congress demanding that Saturn be declared imaginary, and even if Congress passed a law declaring Saturn imaginary, it wouldn't suddenly vanish into the (non-existent) ether. Saturn would continue to circle the sun as always.

So, what should be scientists do about the millions of people still angry about Pluto? We can give in and say, "you're all right, Pluto's a planet." That solution would make people happy, but it completely ignores the scientific process. We could come to a scientific consensus, announce the result, and tell people to "deal with it." That solution would reach the scientific truth (whatever that result might be), but it clearly doesn't work (see point 2 above), and it would really tick off the people who pay our salaries. Maybe we should acknowledge the public's interest in the topic while doing our research, reach a scientific conclusion, and all the while try and teach y'all what we are doing, why, and how we reach the conclusions we do? Nah -- that would be hard. And make too much sense.


  1. Keeping my can of worms to myself. But it's nice to hear about the real intention of the change in classification. Thanks :)

  2. The IAU can go back and fix its gaffe of 2006, yet its leaders made a conscious choice not to do so. This makes it look like they are more interested in protecting the IAU's reputation than in a fair, comprehensive, and likely longer-term scientific process. It is not too late for the IAU to admit they goofed and take up your suggestion, which makes much more sense.

    Notably, only one Kuiper Belt Object larger than Pluto has been discovered to date, and that is Eris.

    We don't need to reconsider Pluto's classification so much as to consider that maybe there are more than the two categories of planets we know (terrestrials and jovians). Maybe dwarf planets should be considered a third class of planets. They are planets because they are large enough to be in hydrostatic equilibrium but of the dwarf variety because they do not gravitationally dominate their orbits. This would be consistent with the use of the term dwarf in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies.

    The process of how something is done is just as important as the outcome it generates. In the case of the IAU, there is clearly a very closed process, no allowance of electronic voting for those who cannot be in a particular room on a particular day, the problematic acceptance of a decision that violated the group's own bylaws, and the fact that many planetary scientists are not IAU members. All these factors need to be addressed.

    Knowing we have missions on the way to Ceres and Pluto, doesn't it make more sense to hold off on any specific definition until the new data is in?