Another “Planet” Debate

CFA Asks “What is a Planet?”

It’s been a few years since the great “Define a Planet” vote took place at the International Astronomical Union meeting. That 2006 event touched off what still remains a firestorm of controversy about what is or isn’t a planet, and in particular, whether Pluto fits the definition set out in the vote. I’ve blogged about this a few times, and my viewpoint has remained pretty constant: Pluto is a dwarf planet. That’s still a planet, but the term “dwarf” tells us something about its place in the size hierarchy of planets in our solar system. However, my opinion is just that: my opinion, based on what my understanding of the issues involved.

It seems to me that the planetary science community is best fitted to determine how we define planets. It’s also very clear that NOTHING in science should ever be up for a vote. That’s not the way science works. It’s not a democracy. It’s based on making decisions based on the clearest FACTS possible. In my opinion, the IAU vote didn’t do that, and it also wasted the time of a lot of scientists who are best-able to define the term “planet”.

Today the whole planet debate thing has really gotten out of hand (in my opinion). We need science to help determine how and why we sort objects in the solar system. It really should be that simple. Instead, we have Pluto huggers demanding planetary status for Pluto (as if it’s something you can picket about) and Pluto demoters saying it doesn’t fit in the IAU definition. We also have anti-Neil deGrasse Tyson crowds and pro-Neil deGrasse Tyson supporters, each loudly disputing the other due to Neil’s outspoken pronouncement that Pluto is NOT a planet.

Over in the corner, quietly working away, we have planetary scientists who are trying to make sense of all the different worlds in the solar system that we DO have, and how to best characterize them. Of all the groups, I have the most sympathy and support for the planetary scientists. They ARE the ones who should be figuring this out. Some of them are working on the New Horizons mission, which is on its way to Pluto and beyond. If the planetary science community decides that Pluto does or doesn’t fit into the definition of comet that the IAU voted in (without the input of a number of planetary scientists), then I’m sure they’ll let us know why and what the facts are that support the decision. And that is the way it should be. Their insights are what should guide the definition of planet.

By way of helping the public understand what the issues are, and what implications they have for how we understand exoplanets (worlds around other stars), the Harvard Center for Astrophysics is having a debate about planets — what they are and how we understand them. It will feature Dr. Owen Gingrich, who chaired a definition committee appointed by the IAU, Dr. Gareth Williams, the associate director of the Minor Planet Center (who will cover for the IAU), and Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative. All three are very eloquent speakers and should provide interesting insights into the central problem of defining “planet”.  The debate will be livestreamed at the Observatory Nights Youtube site at Harvard CFA. I urge you to watch the debate. It should be informative. It probably won’t change too many minds that are already made up, but I hope it will give people some historical and scientific background on the roots of the debate about planets.