If we ever do, or have been, visited by aliens from outer space we'd never know it. The Immigration and Naturalization Service would haul their asses off to jail. They'd never let them out.

"They aren't citizens, they don't have visas and we can't send them back. We have to keep them", the head of the INS says.

"They're from space! This is the single most important event in history! You have to turn them over!", the President yells.

"Umm, sir, you're the President and all but I have the law on my side", the INS head replies.

"You dumbass, this is an order!!"

"Order? Order, sir? Sir, I'm a civil servant. You don't give me orders. I have a job to do and I'm damn well going to do it. Good day".