Moon's Mysteries: Seismic Stories

The Apollo missions, apart from their primary goal of landing humans on the Moon, undertook an exceptional scientific endeavor. Instruments known as Passive Seismic Experiments (PSE) were carefully positioned by astronauts across various lunar landscapes. Designed to persevere in the harsh conditions of space, these instruments diligently recorded data for over a year after the Apollo crew left the lunar surface.

Two distinct versions of the PSE were deployed: the Apollo 11 mission saw the setup of the Early Apollo Surface Experiments Package (EASEP) units, showcased in Figure 1. In contrast, the Apollo 12, 14, 15, and 16 missions favored the advanced Apollo Lunar Surface Experiments Package (ALSEP) units, depicted in Figure 2. The heart of these instruments was the seismometer, which captured moonquakes, meteoritic impacts, and even man-made disturbances. This precious data, sent back to Earth, offers invaluable insights even today, presenting a vivid account of the Moon's geological activities.

Delving into NASA's Planetary Data System reveals an updated lunar seismic dataset, complete with details such as date, time, coordinates, magnitude, and depth. Intriguingly, many moonquakes were found to be synchronized with the Moon's day-night cycle, particularly during sunset and sunrise. The rapid temperature shifts during these transitions, especially near the terminator line, seem to play a role. Moreover, a significant portion of these quakes appear to align with the Moon's known fault lines, hinting at an active lunar geology.