 Over the next six days , 21 distinct impacts were observed , with the largest coming on July 18 at 07 : 33 UTC when fragment G struck Jupiter . This impact created a giant dark spot over 12 @,@ 000 km across , and was estimated to have released an energy equivalent to 6 @,@ 000 @,@ 000 megatons of TNT ( 600 times the world 's nuclear arsenal ) . Two impacts 12 hours apart on July 19 created impact marks of similar size to that caused by fragment G , and impacts continued until July 22 , when fragment W struck the planet . 
