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Originally posted by kiwifoot
Take a look at the enlarged view, all the way to the left, just above the rock, on the horizon, there is a white object, which looks remarkably like a signpost!
Two experiments, the Active Seismic Experiment on Apollo 14 and 16 and the Lunar Seismic Profiling Experiment on Apollo 17, were performed to determine the detailed structure of the upper kilometer of the lunar crust. Both experiments involved detonation of a series of small explosives. The seismic waves or ground motions caused by these explosions were measured by a network of geophones. On Apollo 14 and 16, up to 19 explosions were detonated by an astronaut using a device called a "thumper" along a 90-meter-long geophone line. On Apollo 16, three mortar shells were also used to lob explosive charges to distances of up to 900 meters from the ALSEP. On Apollo 17, eight explosive charges were positioned during the three EVAs at distances of up to 3.5 kilometers from the LM. These charges had masses of 57 grams to 2.7 kilograms. Both the Apollo 16 mortar shells and the Apollo 17 explosives were detonated by radio control after the astronauts left the lunar surface.