As some of my readers will probably know quite well, every astronomer’s favourite argument of what exactly a planet is has been drifting in and out of discussions for years now. This delightful nest of conversational wasps was recently shaken up again by none other than Alan Stern, the scientist behind NASA’s New Horizons mission to Pluto. And I’m very much inclined to take his side in the discussion.
You wouldn’t think it would be that difficult to define something like a planet, seeing as we live on one. However, you’d be mistaken. In science, we like to have good definitions of things. They’re sometimes surprising and may take things into account that you wouldn’t normally consider. This is the way of science, after all. Unfortunately… Well. To say that scientists don’t always agree on things would be an overwhelming understatement.
Stern’s argument is that planets should be defined geophysically, as he outlines in a recent paper. To me, this makes a lot of sense – even if it would suddenly mean that the Solar System is full of 110 planets. If this sounds like a lot to teach kids in school, remember that there were 151 Pokémon in the original game. This would include, among others, such places as Titan, Ganymede, Ceres, Enceladus, and Earth’s moon.
Everyone seems to focus on Pluto as the centre of the argument, but to me it’s incidental. I don’t care so much about Pluto’s planetary status. I do care about the fact that the IAU’s definition of a planet is needlessly convoluted and all kinds of problematic. Nonetheless, this is the decision which the IAU council came to.
In the words of Nick Fury…
This is a big topic, and I have a lot to discuss on it. This includes summarising conversations I’ve had with various people. So I’m not going to try and tackle it all at once. Instead, I’m going to write a series of blog posts (probably 4 or 5) on various aspects of the whole planet not-a-planet debacle.
I would, of course, appreciate any discussion and feedback anyone else wants to give on the matter as and when I post these. Even if you disagree with what I’m saying. Perhaps especially if you disagree with what I’m saying.
Let’s break this all down and see what we can build from the pieces.