An earlier article talks about how the 13th Apollo mission might have ended, without the heroic efforts of the ground crew.  But as part of the rescue process, Apollo 13’s Saturn IV-B rocket stage was jettisoned, and aimed to crash into the Moon.  The rocket, weighing fourteen tons and travelling at 2.5 kilometres per second, slammed into the moon with the force of ten tons of TNT exploding, and left a crater some 35 meters across.  This new image from the Lunar Reconnaissance Orbiter shows the impact site clearly.  For more information, check this article from Sky and Telescope magazine.