Say I wanted to create an impact similar to an asteroid with a diameter of 1.5 kilometer/1 mile with an iron core. It would be going about 18km/s on a 90 degree angle. An impact to level cities but not disturb the Earth as a whole a lot.
Now iron is far from dense compared to some other materials. If I artificially produced a projectile from tungsten, what would the dimensions of the projectile be to cause the same impact damage?
My Original plan was to use asteroids farmed in the solar system but reading up on Project Thor it got me thinking. A species that can use asteroids for planetary bombardment, uses FTL. Such a projectile isn't an insane investment.