While the press has been busy lamenting the demotion of Pluto to mere “dwarf planet” status and fretting about how museum exhibits, grade school textbooks and solar system kits will all have to be changed, we can’t forget that reexamination of definitions and nomenclature is an important part of science. It’s a good sign that scientists are gaining new knowledge and need to incorporate it into an existing body of knowledge.
An interesting commentary in the Globe today reminds us that we need to have good definitions and names for things to allow scientists to study them properly. We needed systems for naming chemicals and organisms before breakthroughs could be made in chemistry and biology.
And so while it may seem amusing, trivial or even ridiculous that there’s a controversy over what is a “planet”, it’s a perhaps a good sign that more discovery is yet to come from the world of astronomy.
The planet definition the IAU came up with is not a good definition; it’s a terrible one. First, by stating that a dwarf planet is not a planet at all, the definition makes no linguistic sense. It’s like saying a grizzly bear is not a bear. This usage also goes against existing nomenclature in astronomy—dwarf stars are still considered stars, and dwarf galaxies are still considered galaxies. The definition is flawed in that it defines an object solely by where it is while ignoring what it is. If Earth were in Pluto’s orbit, according to the IAU definition, it would not be a planet either. How can this be considered a “good definition?” Also, what does it mean for an object to “clear its orbit?” Applied literally, that phrase excludes all planets in our solar system, as all have asteroids in their orbital fields, and Neptune does not clear its orbit of Pluto. The problem here is that the IAU artificially narrowed the term planet at a time when discoveries in this and other solar systems indicate we should be broadening it to encompass the wide variety of objects being discovered. Keep the term planet broad to indicate any non-self-luminous spheroidal object orbiting a star, and then distinguish between types of planets through use of subcategories. This is a far better choice.