On April 14th, 1970, a new crater was carved into the surface of the Moon:
How do we know it's new? Because we made it.That's the impact scar of the third stage of the Saturn V rocket (technically designated S-IVB) that carried Apollo 13 to -- but sadly, not on -- the Moon. Earlier missions had placed seismic instruments on the lunar surface to measure if the Moon had any activity. They found it did, and in fact several moonquakes were big enough that had you been standing there, you would have felt them quite strongly (and probably been knocked on your spacesuit's backside).
The S-IVB upper stage accelerated the astronauts to the Moon from Earth orbit. Once that was done, they had one final mission: in Apollos 13 - 17 the stages were aimed at the Moon itself, and impacted a few days later. The impacts were detected by ...
