Clark Chapman: About 60 years ago, there were some prescient things written by Ernst Opik, by Ralph Baldwin, and by Fletcher Watson. Only a handful of near-Earth asteroids had been discovered, but they came up with order-of-magnitude-correct understandings about how often a bad thing would happen.rnDavid Morrison: That understanding arose almost without reference to Tunguska. Opik and Gene Shoemaker did some kind-of-heroic calculations based on almost zero data. In the 1950s, we only knew of a few Earth-crossing asteroids and had data on a couple of comets that had come into the inner Solar System. And they, using physical intui-rntion and consistent with each other, made the first predictions of what the impact flux might be. Before that, it was pure arm-waving. Opik and Shoemaker quantified it, and within the right order of magnitude.
展开▼
