Almost anyone reading this post will have at least read Enemy of an Enemy, and should hopefully remember the battle for Arken IV. That battle was won through the use of large rocks that pummeled the planet. Over the years I have had some people question me on that. I did in fact spend months researching the attack, years ago when I wrote that scene, and I am sure my description is accurate.
Today I came across this video put out by the Discovery Channel that shows what one big rock would do to the Earth. In the book, dozens of rocks were used, so picture this… but much worse. I would say it would be effective, no?