I've always speculated that before an advanced alien civilization would enter our atmosphere (or land on our planet) - aside from an accidental crash landing type scenario - they would find a way to communicate with us from a safe distance, both for their own safety and ours.
They would be stupid not to try to start a dialogue to guage our personalities. To see if we're hostile toward them or to see if they in fact
could enter our atmosphere safely. It could very well be that we could cough on them and kill them, or vice versa.
It doesn't seem very logical to me that we get surprised by an alien craft. If they have managed interstellar travel, are advanced and intelligent, they would know that dialogue from a safe distance is the best way to proceed.
Maybe they simply travelled all this way to entertain us; maybe they're super hilarious and are part of an interstellar vaudeville-type comedy troup. Lord knows we could use it, SNL blows these days.
- Oni