Meep Merp

Genuinely a better question than most people realize. Apollo 11 left a 2-foot wide panel of mirrors on the lunar surface in 1969. No power source, no wiring, no maintenance. Scientists have been shooting lasers at it from New Mexico ever since. The beam travels 239,000 miles, bounces off the mirrors, and returns in 2.5 seconds. That round trip is how we know the moon is drifting away from Earth at 3.8 centimeters per year. So yes, in a literal sense, they were checking if it would still be there. The seismometers are the part that gets wild. Apollo 12 deliberately crashed its lunar module into the surface at 6,048 km/h. Scientists expected a brief shudder. The moon vibrated for over 55 minutes. On Earth, seismic waves from an equivalent impact die in seconds. Nobody had predicted this. So NASA did it again. Apollo 13 dropped its S-IVB rocket stage from orbit. Hit with the force of 11.5 tons of TNT. The vibrations lasted nearly three and a half hours. The reason is water, or the lack of it. Earth's interior is damp. Moisture in rock acts like a sponge, absorbing seismic energy. The moon is bone dry, cool, and rigid. Shockwaves have nothing to absorb them. They just bounce back and forth through solid stone until the rock itself stops vibrating. Scientists described it as the moon ringing like a bell. The seismometers ran for almost 8 years and detected over 13,000 seismic events. Turns out the moon has four types of quakes: deep ones caused by Earth's gravitational pull, shallow ones from the crust shrinking as the interior cools, thermal ones when sunrise thaws the frozen surface, and impacts from meteorites. In 2023, Caltech reanalyzed old Apollo 17 data and found a fifth type: the lunar lander itself creaking and popping every morning as the sun heated it. Every five to six minutes, for five to seven hours straight. They went up to prove the moon was once part of Earth, measure how fast it's leaving, and figure out what's happening inside a world with no atmosphere, no water, and no tectonic plates. "Checking if it was still there" is honestly closer to the truth than most people's actual answer.