I completely agree with you, as usual, Kaju. It would be fair to say that it is unowned.
But I recall reading something different in MES, that once labour is mixed with nature that it remains the owners’ or his assigns’ land. So, according to Rothbard, if Crusoe were to homestead some part of the island, abandon it for 50 years, then he could legitimately remove any person living on that land, as the land is Crusoe’s “in perpetuity”. This is probably one of the few things that I disagree on with Murray.
Nope. You don’t gain ownership of the ocean by pouring a tin of tomato juice in it.
Your question is another variant of the “lifeboat situation”. Rothbard deals with these in a chapter of TEOL.
This also remids me of a different thread called Anarcho-capitalism defeated? where the OP constructed a hypothetical scenario involving a Star Trek transporter machine.
Frankly if aliens had the ability to destroy the sun then our pewny ammunition would hardly put up much of a fight in defending it.