Over on Planet Four Talk moderator wassock found this Martian double crater in the HiRise images:
which can only have been created by 2 simultaneous impacts.
He messaged me to ask if we had found anything similar on the Moon and also sent a further image of a laboratory test of a high velocity simultaneous impact by 2 objects:
Here are some lunar doubles:
Messier A (on the left – most likely created by separate events)
None of these examples has the distinctive “equatorial” ejecta pattern of first 2 images which I have never seen on the Moon. Why might that be? Well, we know that Mars and the Moon differ geologically so maybe the type of impacted surface and bedrock plays a role. Did the impact take place when Mars was much wetter/ muddier than it is now? Mars also has a more dynamic atmosphere. Would any of these differences account for the distinctive formation of the Martian doubles and ejecta pattern? Maybe the angle and velocity of impact is relevant here too and these double craters form only from high velocity overhead impacts. Wassock says he has found more Martian examples. On a quick ...