What is of particular interest in that image Norval posted is the patterned variability. The crater chain from left to right has 3 craters the same size, 3 slightly larger, the middle crater the largest, 3 craters slightly smaller than the middle one, then finally 3 craters the same size as the first three.
ooooooooooooo
This illustrates that the delivery system (mechanism) for this crater chain can vary the scale of the crater to match the shouldering crater and shoulder a larger or smaller crater. Now that is precision, unmatched by mechanisms devised by any country or science here on earth. Also no country or science here on earth has ever made a single crater the size of even one of these craters, let alone a crater one mile in size, when these crater chains run for miles and miles.
Compare the 13-strike crater chain to this crater chain where all the craters are shoulder to shoulder and the same size, illustrating unprecedented precision. One crater shoulders the next without collapsing the shoulder and making a trench.
http://www2.jpl.nasa.gov/galileo/callisto/022897.html
http://antwrp.gsfc.nasa.gov/apod/ap971209.html
Shoemaker-levy 9 doesn’t even enter into comparison so you might as well shove the Shoemaker-levy
losenger in your pocket to suck on it later on your own time.