Illustration of the pancake model presented by Chyba et al. (1993). The fragmentation starts when the ram pressure, P, exceeds the initial bulk strength, S₀. And the airburst occurs, or the peak brightness is reached, at the very short moment when the windward radius of the object expands to N times the initial diameter of the object, R₀. The height of fragmentation is the altitude where the fragmentation begins, which differs from the height of the airburst or, equivalently, the peak brightness.