It shouldn't be so difficult to determine what a planet is. When you're watching a science fiction show like 'Star Trek' and they show up at some object in space and turn on the viewfinder, the audience and the people in the show know immediately whether it's a planet or a star or a comet or an asteroid.

In science, we take large numbers of disparate facts and reduce them to see patterns. We use the patterns to reduce the amount of information. It's the reason we name species and genera and families in biology. It's also the reason we have names for certain types of geological features and so on in other fields.

A river is a river, independent of whether there are other rivers nearby. In science, we call things what they are based on their attributes, not what they're next to.

Alan Stern Quotes