An object flying through the solar system from interstellar space, called Oumuamua, has been suspected of being an alien spacecraft instead of a stray asteroid, because it is cigar-shaped, like a spaceship (Also like a zeppelin, a submarine, a cheesesteak, or, let’s face it, a cigar). But nobody suspects it of being A Giant Stogie from Beyond, because we are scanning it for signs of alien life.
And we are not finding any, but that, according to some thinkers, is not enough to rule out Oumuamua from being a space vessel crammed full of aliens. These people think that the aliens aboard the thing have gone silent, even turning off their cell phones, so we don’t figure out what they are up to. They are like the crew of a U-boat, keeping deadly quiet to keep sonar from pinging them, until one fat Nazi drops a wrench on the floor and they get the shit depth-charged out of them. We’ve all seen that movie.
This assumes that the aliens are afraid of being attacked by us. Why they would be, nobody knows, except maybe they know humans have always attacked anything they ran across, most especially each other, and the aliens may just be exhibiting an abundance of caution, figuring that if we knew they existed, we would start a crash program to build a ship faster than theirs, with the express purpose of catching them and blowing them into stardust.
In the meantime, the Oumuamuans are heading out to the stars at 190,000 or so miles an hour, which, to put it in more comprehensible terms, is disappearing nearly as fast as a friend who owes you money.
You can’t blame them for that, though. Assuming aliens would make contact peacefully, which is a possibility as long as they land anywhere on Earth outside of the southern United States, what are they going to do with us? There are only a couple of conceivable outcomes. One, they could attempt to raise us to be an advanced star-faring civilization like they are, staying chill for century upon century while exploring the galaxy. This would be a crap-ton of work for them, considering most of us can barely sit still on an airplane for a few hours without at least a bag of nuts and a cocktail.
Secondly, they could conquer us and make us their slaves. This might have been a good idea a hundred years ago, when people used to work, but now that most of us just share pictures of our genitals via smartphone and consider that an accomplishment, turning us into productive forced labor probably wouldn’t be worth the effort.
Thirdly, they could exterminate us and take over the Earth. It’s probably more cost-effective for them to let us exterminate ourselves, however, which seems more likely by the day, and move into the vacant property.
You don't even have to be that advanced to figure that one out.