On badastronomy, Phil posted an opinion piece about what defines a planet, the status of Pluto, and announcing the Great Planet Debate in John Hopkins University with Neil Tysson and Mark Sykes. (So exciting!) Anyways, tread carefully while reading this. I am not an expert in anything.
I mostly agree about Phil on this one. The definitions for planets are blurry, and as more discoveries are made, it may become even blurrier. I also think that trying to classify them is important, though. It may help people understand them better. My opinion is that Pluto is not a planet. It is kind of insignificant, considering how many of Pluto like objects are out there. Not only that, it is smaller than Ganymedes, Callisto, Triton, Earth’s moon, Europa, Io, and Titan! But then again, the amount of something or the uniqueness of it doesn’t prevent something to be classified into certain labels. Anyways, current definitions are unsatisfactory, and as Phil said, if Earth would have been very far away, it couldn’t be a planet because it wouldn’t exert a strong gravitational influence over such a large volumes of space. So, what are the three qualifications that make an object a planet? They are:
1. The object must have enough mass for its shape to be influenced by gravity into a sphere.
2. They must orbit a star.
3. They must have cleared objects around its orbit.
From what I know, they came to this decision through the votes of a confefence by International Astronomical Union. There were definitions that included Ceres, Pluto, Charon, and Eris into planethood. In the end, though, they voted to those three definitions. Pluto was, well, plutoed (it is an actual word that stemmed from the debacle!) into a dwarf planet. So, how did all of these came to be?
It began with discoveries of Trans Neptunian objects, obviously objects that are beyond the orbit of Neptune, other than Pluto. At the time, though, they weren’t a concern to Pluto’s planetary status, since Pluto was still larger. As more discoveries, were made, though, Pluto’s status came into questioning. Especially after astronomer Mike Brown’s survey of the objects. He was coming up with new somewhat large objects all the time, like Quaoar and Sedna. The trigger, though, was pulled with the discovery of Eris (the goddess of discord, which is an ironic name, considering what happened next) (nicknamed Xena). This caused astronomers to try to define what constitutes a planet. And it all culminated in the meeting above.
I think this is all really cool. It is science in action, with things changing after new evidences arrive. The decision may have been unpopular (even with me), and the debate may not be over yet, but science doesn’t go for what feels good. It goes for what is the best evidence they can come up with at the moment. Hopefully, over the next few years, they can solve this major problem of classifying these objects.