Apollo 14 
AUDIO: Apollo 12 seismometer SFX
What sounds like an early video game is really the sound of the Moon rattling after it took a big hit. A seismometer left on the Moon by the astronauts of Apollo 12 recorded the rattling 40 years ago today, when the booster rocket of the Apollo 14 mission slammed into the lunar surface. [more SFX]
In all, five of the Apollo missions left seismometers on the surface, and four of those operated until the network was shut down in 1977. They recorded thousands of moonquakes. Some were triggered by impacts, while others were generated deep within the Moon itself. The quakes helped scientists probe the Moon's interior.
The computers of the day were too limited to analyze all of the observations. In recent years, though, teams of scientists have re-analyzed the data. They've found that there were a lot more moonquakes than they'd thought.
Many of the quakes were generated hundreds of miles below the surface -- perhaps triggered by the pull of Earth's gravity as the Moon orbits our planet. And most of them came from the side of the Moon that always faces Earth, suggesting that there may be a difference in the structure of the nearside and the farside.
While Apollo 14's first scientific goal was to create a big impact with its booster rocket, its main goal was to explore a region that was created by a much bigger impact. More about that tomorrow.
Script by Damond Benningfield, Copyright 2010