What do you think of this fact?
What do you do with a lunar module you no longer need? In 1969, NASA had a clear answer: throw it. At the Moon. On purpose.
A crash as an experiment
During the Apollo 12 mission, astronauts set up a seismometer on the Moon, an instrument that measures ground shaking. To calibrate it, scientists needed a jolt whose strength and location they knew exactly.
So once the crew had moved back into the command module, Mission Control sent a command to the ascent stage of the lunar module Intrepid. According to NASA, its thrusters fired for 83 seconds, it dropped out of orbit and struck the surface about 40 miles, or roughly 64 kilometers, from the seismometer. Popular Science puts the impact at roughly the force of one ton of TNT.
The Moon wouldn’t stop shaking
Then came the surprise. According to NASA, the seismometer recorded signals for nearly an hour after the impact. Popular Science describes how the wave peaked within eight minutes and took about an hour to fully fade. It was, as the magazine puts it, almost as if the Moon was ringing like a bell.
On Earth, a quake like that would be over much faster. The reason is water: moisture in rock soaks up a large part of the energy. The Moon, by contrast, is bone dry and rigid. With no water to dampen them, the vibrations keep bouncing back and forth through the rock until they finally die out.
Bonus fact: For Apollo 13, NASA crashed a spent rocket stage into the Moon. According to Popular Science, its shockwaves were about 30 times greater and four times longer than those from the Apollo 12 crash.
A Moon struck like a bell, with science taking notes.