It seems like every time I write an article about Pluto or any other denizen of the realm of the solar system that lies beyond Neptune, the comments on the article are overwhelmed by people who are unhappy with the IAU redefinition of the word "planet" and the consequent reclassification of Pluto. I understand that many people care a lot about this subject, but I find it to be pretty much the least interesting conversation to have about the fascinating worlds at the edge of our solar system. The inevitable comment arguments have actually made me wary of writing about Pluto and friends at all. And recently it's been particularly wearisome, as the participants in the conversation have accused me in comments here and on other websites of mindless sycophancy to one of the personalities in the public debate.
I've had enough. I want to be able to write about Pluto and Eris and all their neighbors without devolving into the planet-definition conversation every single time. I want to be able to discuss the fun problem of not knowing which of the two biggest trans-Neptunian objects is larger without people accusing me of irrational favoritism of one or the other and suggesting I should be fired for what I wrote. With New Horizons beginning its approach to Pluto and Charon, we are about to enter an extraordinarily productive period of scientific discovery. Pluto is an excitingly in-between world, occupying a place on the borders of so many different classes of objects, likely experiencing (or having experienced) a huge array of different processes. Studying it will inform the study of worlds across the rest of the solar system. I want to share all of that with you without constantly having to fight inappropriate behavior in the comments.
The Planetary Society is a community of space enthusiasts, both professional and amateur, of which I am merely a member, and I firmly believe in the importance of providing a forum for our community to talk amongst ourselves. Some terrific things have happened thanks to the comments on blog posts. It usually works pretty well. Except, it seems, whenever I mention Pluto.
I recognize that many of you care deeply about the topic of the IAU planet definition, and if that's the conversation you want to have about Pluto, then I'm happy to give you that opportunity, but only here. I believe that the overwhelming majority of you are capable of discussing it without resorting to ad hominem attacks and other bad behavior. This post is for you. Here, you may discuss the definition all you like, advocate whatever position you like, as long as you adhere to our comment policy, which is displayed prominently on the page once you log in to comment. If you don't adhere to the policy, your comment privileges will be revoked.
At the risk of being too idealistic, I'd like to suggest people read before arguing. There is a lot to read on the subject. For some background, here's the Wikipedia page on the IAU definition, which has lots of links to the history. Here is the full text of the IAU's Resolution B5 (PDF). For opinions, there are famous advocates for "it's not a planet," including our own Board member (and former President), Neil Tyson, who took Pluto off his list of planets at the Hayden Planetarium in 2000, writing about that in his book and NOVA show The Pluto Files. There's also Mike Brown, author of How I Killed Pluto and Why It Had It Coming, who blogs frequently about Pluto and planethood. The most vocal advocate for "it's still a planet" is, without a doubt, New Horizons Principal Investigator Alan Stern, who laid out his position on his PI's Perspective blog in an entry titled "Unabashedly Onward to the Ninth Planet". Alan's opinion carries weight, as he literally wrote the book on the science of Pluto and Charon, with coauthor Jacqueline Mitton, and will no doubt be updating that book with great new science in a couple of years. Joining Alan in support of Pluto's planethood is journalist Alan Boyle, who also wrote a book, The Case for Pluto. Recently, Astronomy editor David Eicher posted a video supporting "the IAU definition is stupid" camp. David Grinspoon has written eloquently about two really strange aspects of the definition (that dwarf planets are not planets, and that exoplanets aren't covered). There are lots of others; feel free to comment with links to other good, thoughtful writing on the subject.
In my own work, I do my best to emulate what the scientific community does, to the extent that there is consensus in the community. I expect that once New Horizons returns its expected beautiful images of Pluto, I'll hear more scientists referring to it as a "planet." That's based upon the assumption that it'll become a world with geology. Probably. Maybe. We actually don't know yet, of course. If it looks heavily cratered like the Moon, perhaps people will be less inclined to switch their usage. Maybe Pluto will be in the middle, and, like Titan, endure Jeff Moore's accusation of being "Callisto with weather," in which case the people who think it's more active will be more inclined to call it a planet, and the people who think it's a dead world with a veneer of weather will not! I look forward to the arguments about what Pluto is, and you'll see my language evolve as the scientific community learns more and adjusts their language accordingly. As I've said before, edge cases are fun. They test our understanding of how the physics of the solar system's formation and evolution work. And, more often than not, we find out we were wrong about at least some of what we thought we knew. That's what you'll see me talking about elsewhere on this site.
So, feel free to discuss the planet definition, its shortcomings, et cetera, here. Keep it polite. Most importantly, on planetary.org, keep it here. Elsewhere, I want to talk with readers about what we are learning about Pluto and its neighbors -- not what words a few English-speaking people choose to use to refer to it.