Interestingly, there actually exists an Outer Space Treaty. [1] [2] (aka "Treaty on Principles Governing the Activities of States
in the Exploration and Use of Outer Space, including
the Moon and Other Celestial Bodies")
It was initially promulgated by the USA, UK and [then] USSR in 1967, a 100 countries are currently party to it (with a further 26 signatories pending ratification], and it explicitly says, "outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means".
All this is under the ambit of the United Nations Office for Outer Space Affairs.
Personally, the cynic in me can't help but believe that the USA was an eager initial party to this because they were terrified that the Soviet Union would pip them to the Moon-post.
It was initially promulgated by the USA, UK and [then] USSR in 1967, a 100 countries are currently party to it (with a further 26 signatories pending ratification], and it explicitly says, "outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means".
All this is under the ambit of the United Nations Office for Outer Space Affairs.
Personally, the cynic in me can't help but believe that the USA was an eager initial party to this because they were terrified that the Soviet Union would pip them to the Moon-post.
[1] http://en.wikipedia.org/wiki/Outer_Space_Treaty
[2] http://www.oosa.unvienna.org/oosa/SpaceLaw/outerspt.html