Note: The laws governing ownership of things like planets and star systems are complex, to say the very least. Fortunately, most civilized races will defend the general concept of ownership out of simple self-interest (read: "the desire to hang on to their own stuff".) Jurisdiction in these matters may look like a gordian knot, but there are plenty of powerful governments with scissors, swords, and starships who will be happy to settle matters.
MURTAUGH: Ennesby, you've got too much imagination, and not enough actual imagination.
MURTAUGH: Here's what we do: signal the colony below. "We found your world on a map, and its location is no longer a secret."
"It appears indefensible. Would you like us to help you evacuate before the mob arrives?"
MURTAUGH: Made in good faith, that offer puts us under Samaritan clauses.
Boom. We're here legally.
KEVYN: Are we the good guys if we're this crafty about being the good guys?
MURTAUGH: I'm a career good-guy. This qualifies as "justifiably crafty righteousness."