To answer this question you have to understand the idea of the property on Earth. All monetary matters are subject to social approvement, in other words, "דינא דמלכותא דינא".
So imagine you find an iceberg in Island and you'd like to privatize it - is it Halachicly yours? THe only way to answer this is to ask others - It makes no sense of having a property with no humans around, think about that.
So there is no difference in boundaries for that social approval - you might claim you own 5 square miles on Uranus, but as long as there's no existing agreement about Uranus, your claim is meaningless.