57:6.4

If space bodies are similar in size and density, collisions may occur. But if two space bodies of similar density are relatively unequal in size, then, if the smaller progressively approaches the larger, the disruption of the smaller body will occur when the radius of its orbit becomes less than two and one-half times the radius of the larger body. Collisions among the giants of space are rare indeed, but these gravity-tidal explosions of lesser bodies are quite common.