Just wondering here, how much energy (in Joules or Mtons) would an asteroid say 15 km wide have if it impacted the moon at 99.9% the speed of light? btw, I'm trying to figure this calculation out in terms of SR where the mass of the asteroid would appear much greater than if it was traveling at classical speeds. Also what would we see from the Earth if this hit the moon? I know that a really large asteroid hitting the moon at high classical, but still possible, speeds could create a blast as bright as the sun. So at 99.9% of c the people on the wrong side of Earth would be toast right? Effects on the moon?