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.