The Great Planet Debate: an information science question and public understanding of science issue
I attended the Great Planet Debate
between Mark Sykes (Planetary Science Institute
) and Neil deGrasse Tyson (American Museum of Natural History
) today -- in person. It was moderated by Ira Flatow and will be made available at that web site.
This was really fun. If you're not into planetary science (how could you not be? but I hear that there are people out there aren't), the debate revolves (intended) around:
- what defines a planet?
- is there a point in using the term "planet" at all?
- for some - what role does IAU have in this?
- for some - if this discussion is that important to science, how can it be decided by vote? Can a vote be called consensus, even if it's 90% in favor of one side?
Used to be that just about anything in the sky at night was called a planet. But over time, asteroids, stars,.... other things were identified and named. So we sort of know what a planet is - and thanks to powerful telescopes and robotic missions - we know a lot about a lot of planets. If we have a whole loosely defined pile of things, is the term useful? When scientists talk to scientists, can they use the term planet and be understood?
IAU is an international body with the job of naming things. They name things for use in science, so there is some common ground. They work towards consensus on the names. Naming things sometimes depends on first agreeing what they are. In a meeting in Prague, they had a vote: how do we define planet? Their definition is:
(1) 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 neighbourhood around its orbit.
(2) A "dwarf 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, (c) has not cleared the neighbourhood around its orbit, and
(d) is not a satellite.
(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies" [from]
This is all pretty unsatisfying for many people, because it clearly doesn't apply to exo planets - things not going around our Sun. Apparently the clearing the neighborhood thing isn't clear either.
What I got from the debate was that Sykes wants to call a lot more things planets, and Tyson wants to call nothing planets, because the term isn't useful. He said we need a new lexicon to group like things like the rocky ones, the gassy ones, the things in the Kuiper Belt....
It gets even more interesting when you realize how much this has become not a science issue, but a classification problem, sociology of science problem, and a public understanding of science problem (which I am using to include public communication and also science education).
There's a lot of philosophy, cognitive science, and sociology on how people put things into categories. Sykes was arguing for a hierarchical model with "planet" being the highest level with the only definition really being that they are 1) round 2) not a star 3) not a satellite (although this last point seemed a bit flexible). He argues that there is a common understanding of what you mean when you say planet and that we need a way to refer to all of these things and none of this precludes sub-categories.
Tyson says "planet" is useless, and furthermore, that it will restrict our vision for further exploration. He points to some of the advertising for New Horizons that seemed to indicate that this mission would complete planetary expeditions. Historically, apparently science was held back because scientists didn't believe their observations because they thought that they already knew all of the planets.
The public understanding part of this is interesting, too. Tyson's argument is in part that the whole idea that learning science is being able to enumerate a set number of planets is faulty. In other words, science and science literacy should be about the joy of discovery or even about understanding the scientific method, not about memorizing and regurgitating a list. Certainly either of these other two versions will set a person up better for lifelong learning, which is a necessity to remain scientifically literate.
But some teachers, many journalists, and lots of the public want a simple answer. They want to know for sure and be told a fact by a scientific authority. They don't want to know that there are controversies in science that are not caused by bad behavior. And the universe is complex, and things aren't always neat and tidy, and humans want to put things in boxes.
As always, I lose steam towards the end, but to sum up:
- good session, watch it when available online
- probably should throw out the IAU definition, but keep the word planet, understanding that it in and of itself is not that informative
- someone - or multiple people - should use this as a case study for both scientific controversies and public understanding of science - and maybe some research question about how scientists categorize things when there is controversy
- teachers should take this opportunity to teach a more nuanced view to their students - to learn from the planetary scientists what's what, and then to teach their students about the wonders of the universe
I recommend the Planetary Society
's podcast and blog for anyone who wants to learn more or who is interested in planetary science.
Oh, and I stayed a bit to try to chat, but Tyson was mobbed - we did get him to autograph one of our library books that he wrote :)