Nothing says "arbitrary" more than a quantity that was deliberately rounded up 9km just for the heck of it. Things can be guided by math/logic and still have a

Nothing says "arbitrary" more than a quantity that was deliberately rounded up 9km just for the heck of it. Things can be guided by math/logic and still have arbitrary elements. The Karmen line definition is a logical definition with certain arbitrary constant selections, and therefore it's not specific. This doesn't mean it's random, only that there are band of valid definitions. It's correct to state a boundary defined by centrifugal force dominance is somewhere between 80ish and 100ish km, and the specific number is somewhat arbitrary. It's not correct to say its for 20km (for example), which would be a truly random selection.