What do you think of this hypothesis about aliens visiting us on earth?

We know that if we travel faster, we go slowly in time and there is no motivation to come back. So, this is a motivation for building very large spaceships where an entire community can travel. Your community travel with you, so the "coming back" does not even make sense. Maybe what I am going to suggest here is not a new hypothesis, but it just came to me. What if some of the large asteroids orbiting some planets in our solar system was in fact a disguised spaceship hiding an entire community of aliens? Ok Ok, I know, it's time that I quit Y!A.