What if the object was already traveling in our rough direction and aliens decided to simply take advantage of the free ride? They tweaked the direction with a few thrusters to pass by Earth, and they left the rotation to help camouflage the object with its natural tumble through space. Finally, they deboarded the object when they reached their desired location nearest to Earth.
It's fun to speculate, but I'm sure the reality of the situation is far more boring.
It's fun to speculate, but I'm sure the reality of the situation is far more boring.