Question: The article mentions that a 1kg projectile travelling at 99% of the speed of light would have such and such more explosive energy than the most powerful nuclear bob ever detonated. I don't doubt the math, but would the destructive effects (e.g. to a city) of such a projectile weapon actually equal those of a nuclear bomb? I'm not talking about the radiation and such in the aftermath, just the explosion itself. Wouldn't the projectile basically go straight through a planet?

Edit: I suppose the shockwave from entering the atmosphere would cause a bit of a rucus too...still interested in any responses.