"If comets do turn out to be space ships of highly advanced beings then we're in deep shiite."
I was thinking the same exact thing.....Our NASA hammer goes off and then the next thing you know a pulsing death beam expands the Gulf coast clean up to Dallas. That would suck.
Maybe I was tipped off by your screen name but do you ever think you spend a little too much time here?
Big time.
There are more mundane possibilities. The interior might be a huge hollow nichol ball. Hitting it at high speed with an 800 lb hammer will produce sonic reverberations that will permanently deafen every creature on the planet with ears.
Even that scenario might include aliens though. To them it might be a dinner bell.