Terminal Ballistics: It Was a Really Bad Day on Earth

I've posted about some aspects of interior and exterior ballistics but I haven't mentioned the last part of the puzzle, terminal ballistics. Approximately 65 million years ago, it was a very bad day for planet earth. An asteroid impacted at hypervelocity speeds and the ensuing disaster killed off a vast percentage of life on earth (nearly 75% of all species). So this post is about terminal ballistics or impact phenomena. 

But first, a video simulating that asteroid impact. The projectile is a nickel/iron mix and the planet is simulated with a layer of water over silica. Consider the scale of the impact. In the model the projectile is scaled such that it would have been about 8 miles long by about 5 miles in diameter. The resulting crater depth would have been nearly 10 miles or roughly twice the height of Mt. Everest.

The projectile is travelling at 10 kilometers/second and the shock wave which progresses away from the impact site would in the real situation have ranged around the planet causing untold amounts of further damage. A huge tsunami would have travelled far and wide and scoured some coastlines completely clean. It was nearly a planet killer. The impact debris cloud from the crater would have persisted for years in the atmosphere and many plant species became extinct along with the dinosaurs and other animals.

The major criteria in terminal ballistics revolves around impact velocity. Below a certain velocity projectile/target material properties play a significant role. Above that velocity both projectile and target act as fluids, where strength and many other material properties don't count. In this region the penetration is one of material erosion.

From the model one can see the projectile stops penetrating into the target after it has completely flowed into the base of the crater. Above a certain velocity the penetration into the target is dependent on the amount of material available for fluid flow. A long projectile at high velocity will penetrate further than a "chunky" projectile.

Other fields of terminal ballistics include projectile/armor interactions, and wound ballistics. The projectile/armor interactions are all defense related issues and tends to be classified. Wound ballistics often ends up in contentious discussions because it involves highly charged subjects such as war, crime, gun violence, and firearm ownership. Though I have never been one to shy away from controversial subjects this post isn't the place for that. Suffice it to say, most of what is "common knowledge" about wound ballistics is stuff bulls leave behind. Some other time perhaps.

I recognize that this post barely sands the first layer off this subject but I have to start somewhere.