But that’s the wrong standard. Because inasmuch as no government yet has the ability to exercise jurisdiction on Mars, no private citizen has the means to “purloin” Mars samples. I see no reason to hold one side of this problem to present technological limitations, but allow the other some unmatched futuristic head start. Particularly as arranging something akin to a drone strike on Mars is probably already achievable with current technology.
The question of how Earth-bound governments might enforce their laws on space pirates is no more open than the question of how a presently Earth-bound humans or their descendants might turn to space piracy. The legality is one thing, the enforcement is another. I am simply positing that when it becomes necessary to exert jurisdiction in space, Earth-bound governments will figure it out from the legislative side soon enough. Or perhaps they will simply apply current legislation, particularly if their own citizens and property are involved. I think it’s fair to assume that if a private citizen has means to break the law in space, then governments will have means to reach out and touch them in some way.
This was literally the hypothetical situation posed by the o.p. If you take issue with even considering that, you need to address that objection to the o.p.
I don’t see where the OP requires such a mismatch. Indeed, the OP doesn’t even seem to require that the perpetrator be off-planet. Launching a rocket with a probe from the US with a mission to steal the samples might also, for instance, fit the bill.
The question posited by the OP (which you did not write) was:
If you are a US citizen, the US can exercise jurisdiction over you even for crimes (against US federal law) committed abroad. If you’re not a US citizen, then I suppose it depends. Are you a US citizen?
I’d also note that, were this not all just a hypothetical, engaging others to come up with a plan to steal these samples (commit larceny) might subject you to charges of conspiracy to, solicitation to, or attempt to commit larceny on that property. So jurisdiction could probably be exercised just as soon as it became apparent you were creating a rocket and a lander for that purpose.
I’d imagine the words of the treaty would matter, then. Because what seems lost in a lot of these discussions about the force of laws in space and space piracy versus international law, etc, etc is how much of it hinges on whether not the waters are “muddied” by the absence of other grounds for jurisdiction. In Antartica, for instance, the problem isn’t so much that the US or any other nation can’t figure out how to try someone for a crime committed in Antarctica, but rather how to unravel the mess of perhaps competing jurisdictions with international research groups and some controversy over whether or not any nation can claim territory on the continent. Which is where the Antarctic Treaty System would come into play.
So with you turning to larceny on Mars (or just designing a probe to accomplish the same, even without leaving Earth yourself), an added hurdle would be whether or not there is some limitation in any US treaty with the UK that might bear on the question of jurisdiction. It may turn out that in your specific case, the answer is trivial. Or it may not. Because while international law and the law of the sea are nice and all, the laws of the US, UK, and the treaties between the two are going to matter more in your specific case.
Which is why I think hypotheticals can be tricky. It may be that some underlying facts of law that we might be tempted to assume away as being beyond the scope of the question (jurisdiction for crimes committed in space) are actually essential to the answer (crimes committed in space against US property by a citizen of the UK).
I suppose an analogous case would be - what if I decided to steal or vandalize fishing nets or lobster traps put out on the high seas (or in the South China Sea), or free-floating scientific research buoys? You car does not stop being your car because you parked it on public property, either.
As mentioned, the distinction is what the government can do to you legally, vs. physically. As Julian Assange may point out, even if the government really doesn’t seem to have a legitimate case, the trick is to get from argument to result.
Treaties might give other countries jurisdiction as well, but the US (as owner of the stolen property) would have jurisdiction regardless. It’s quite possible, even common, for multiple sovereignties to have jurisdiction over the same crime.
