[@Wernher] If we didn't go by rule of cool, you'd all be dead cause you are facing a race who can travel between separate galaxies. That instantly also gives them god tier technology and weapons. 

But we play by rule of cool, with a hint of realism. I am sure a well aimed slug could hit the asteroid. But like I said before, a low albedo asteroid is really hard to identify, especially amongst others. 

(Or you could just nuke the whole fricking asteroid belt)