To go back to the discussion of interplanetary conflict a bit...
You all argue about how easy it is to hit a predictable orbit object, the earth. Absolutely it CAN be easy, if your calculations are right. The problem is the Earth"s natural shieldS. The moon is our shield of last resort. We have everything from Jupiter to the Solar wind working to beat back them alien xenocidal missiles. "But Kogan," you call, "any elementary-grade Folabboxi can compute these variables to decimals our tiny human brains can't comprehend! They will just find that sweet spot and it will get through!"
Well, to answer you, I pose this question. You have a 10" diameter marble launched at .7625c from Alpha centauri towards earth, perfectly aimed at the sweet spot. 1/2 a light year away, you have a stationary butterfly's wing angled 1 degree offset from dead on, perfectly in the path of the marble.
What happens to that marble?
Okay, take away the butterfly's wing and instead add in a few dozen objects with the mass of pluto randomly moved along likely paths of assault. As long as the intellegent agressor has no wamprats back home, we can defeat attacks by missiles we can't really make yet using technology within our reach today. And even if they were successful, we're not that far off from extraterrestrial colonies, and airless areas aren't in danger from this sort of attack. Mankind is on the cusp of being durable like no earth species before, and we're bringing cats and dogs with us. The jury's still out on elephants and dolphins. One thing is for sure, I hope our fellow earthlings aren't as intellegent as some people think they are...