Talking of Shoemaker-Levy 9, there's lots of evidence that fragmented comet/asteroid impacts are quite common and have occurred on Earth as well as on Jupiter and its moons.
Searchng for vestigial crater chains could become a new hobby for anyone interested in the phenomenon.
This site from NASA is fascinating and shows how 'easy' such finds might be made.
Using Google Earth is a brilliant way to skim 50 or 60 miles high over remote terrain looking for tell tale signs. In fact I think I've spotted two craters around Chad not related to the NASA article and not recorded in the standard crater data bases.
Have a go, it's fascinating.
JaX
