Actually, this line can be a good neg, not an approach.
For example, when you approach her and start building rapport, if she says anything that creeps you out, you can simply throw in "Are you sure you're on the right planet?" or "We're on planet Earth, are you sure you're one of us?"

Simply because using this line as an approach is way too awkward. But that's just my opinion.

Or else ask them "what are you doing on my planet?" or " what are you doing in my town? Can I see your permit?"

If it ends bad, why keep using it?

Doesn't even make sense, 'outer space' isn't even a planet.

Don't use a line that makes it easy for a woman to focus on the fact that some randomer has just come up to talk to them with no specific reason other than to ask something stupid and irrelevant. Don't use a line that gives them the opportunity to or even the reason to shoot you down in one sentence. You may aswell open with "There's a party at your ankles and your pants are invited."

Use something that makes them think about an answer, that disarms them and isn't blatantly telling them all you want is to desperately talk to them.

Use a canned line like "My best friends gf is bisexual and she kisses other girls... Do you think that's cheating?" you'll get better reactions and get an honest answer. They'll be dedicated to thinking about this serious question and giving you a meaningful answer.

what planet are you from?

i think a better opener would be. i come up with it right now.
i like this planet. do you?

try it and tell us how that was like.