More About Secondary Craters
Figure 1: Copernicus Crater (LROC Image/ASU/NASA) Large impact craters are surrounded by secondary craters, appearing alone, in clusters, in lines, or even in loops. These craters extend to many crater radii from the primary (see Figure 1). I'm concerned about secondary craters since multiple ejecta projectiles from a large impact could easily strike the surface in proximity to each other simultaneously... looking very much like a doublet crater. Jay Melosh (1989) points out that as the range from the primary crater increases, secondary craters are more dispersed and their shapes are more circular. The improved circularity of distal secondaries results from the projectile's higher velocity, and the highest velocity ejecta is typically going to travel the furthest. The lower density of secondary craters combined with them being more circular, means they look a lot like primary impact craters! Figure 2: Secondary craters High-energy ejecta have a decent chan...