As our flagship class space probe nears the Jovian system it releases a 1000 lb metal ball. The spacecraft inserts into Jupiter's orbit a few weeks later and the metal ball continues on a collision course with Europa. It hits Europa at a speed somewhere in the neighborhood of 60,000 mph. (Would a 1000 lb metal ball at that speed be enough to knock a hole in that ice? If not how big would it need to be?) Of course the hole immediately starts to refreeze, be at that impact location it would be far thinner than the 12 mile average. Couldn't the probe then launch a bunker buster type probe at that thin spot to get a hydrobot (or a number of them) into that ocean?

Easy on me buddy, again I'm an enthusiast, not a scientist.