NASA recently announced its plan to find and capture a small asteroid and place it in a stable orbit near the moon. (If you have a few minutes to spare, check out this cool animation of the proposed mission here.) But would an asteroid-capture mission violate international space law, such as the 1967 Outer Space Treaty or the 1972 Convention on International Liability for Damage Caused by Space Objects? Legal scholars (with nothing better to do) discuss the legality of the asteroid capture mission in this interesting report.
prior probability 
Well, I know this is getting into the theories of property law, but here are few ways it could be looked at:
1) Acquisition by Discovery. Are we the discoverers of this particular asteroid? If we (as the United States, through NASA) discovered it, don’t we have a claim before all others in this “property”?
2) The Labor Theory. Another concept of property law, does not the person who puts the work in to gather the property deserve the right to keep it? An asteroid is of no use to anyone floating out in space, and is essentially worthless (there are tens of millions of them floating throughout space). But once gathered, it becomes useful and valuable, and thus should belong to the worker (in this case NASA for gathering it to study).
– Marcus Steverson
So the question is, does property law apply to outer space?
I don’t think that all property laws could legally apply to outer space because it is considered res communis. Every nation technically shares a border with outer space since sovereignty, according to the United Nations, extends to the heavens (exception being approved flying routes). This is especially true since Sputnik was launched which created a rebus sic stantibus and further led to expansions of sovereignty, but this was not entirely fair for nations who have an equal claim to space but don’t have the means to get there. Therefore, the United Nations takes the stance that acquisition by discovery isn’t a fair doctrine for outer space just as the sun didn’t always set on the British Empire. Additional, in the 1800’s, sovereignty extended to the height a hot air balloon could reach because anything else was impossible at the time and therefore no clarifications were needed on where sovereignty extended. However, I do think that if a nations personal property is in space, they should be held liable for any damages that may result on Earth from falling pieces of a spaceship or satellite.
However, I do think that acquisition by capture is perfectly legal in space. An asteroid, unlike a planet, is an unattached and free flowing object not subject to the orbital patterns that planets are confined to. There could be a reasonable capture of an asteroid similar to the rules of capture with wild animals.
– Devan McGowan
Is an asteroid not a “celestial body”? Treaty law is specific about the non-appropriation of celestial bodies, (Art II, OST) and, at first glance, this appears to be an act enclosure of commonly-held property by a single unauthorised sovereign State. This contravenes the res communis doctrine and the present arrangements for international commons property law.
“Article II, OST: “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.”
Conversely, Art I says “celestial bodies shall be free for exploration and use by all States without discrimination of any kind, on a basis of equality and in accordance with international law, and there shall be free access to all areas of celestial bodies.”
It seems that, as long as the US is not claiming the asteroid as part of its national territory, it is free to “use” it. The same would apply to private organisations.
That is a good argument, but notice there is a significant gap in the treaty, since there is no reference to “capture” per se. (Moreover, at common law and under ancient Roman law principles, the capture of an unowned object, such as a wild animal, is an act of possession conferring the right of ownership on the capturer! See, e.g., Pierson v Post.) So, how should we interpret the treaty in light of this gap? Perhaps we could turn to the common law to fill in these gaps. That is, if the ultimate purpose of the capture mission is to protect Earth, then perhaps the doctrine of necessity might apply to this case.