Well...............
Fucking unnerving to say the least... So other words really work.
Only thing is, if something as huge as a small moon was to head for earth we'd know about it years beforehand, and come up with a defense. Also, if it did happen, it's not for a few hundred years and by then the real Captain Kirk would be in charge of earth's star fleet. So I aint so worried.
I doubt we wil ever have a defence that is cablabe of destroying somthing that size, besides even if we did do you really think it would be wise to put somthing that powerful in human hands?