When they went to the moon, Apollo astronauts placed seismometers on the surface. Those instruments strikingly revealed that the moon experiences moonquakes, just as the Earth experiences earthquakes. In fact, scientists have since determined there are four types of moonquakes: Deep, shallow, thermal and the kind stemming from meteorite impacts.
But a new look at thermal earthquake data recorded by instruments from the Apollo 17 mission has unveiled a fifth and unexpected type of moonquake — one that emanates from the Apollo 17 lunar lander base itself.
During the Apollo 17 mission, scientists calibrated three seismometers to record thermal earthquakes on the moon. Placed on the lunar surface, these devices recorded data from October 1976 to May 1977. Such thermal quakes are caused by intense temperature changes that occur on the moon as it transitions from the lunar day to lunar night, which can swing from 250 degrees Fahrenheit (121 degrees Celsius) to -208 degrees Fahrenheit (-133 degrees Celsius).
Using modern techniques, including machine learning, researchers from the California Institute of Technology reanalyzed the data, determining that thermal quakes occur with very precise regularity the day. But, they also found new tremors in the data that weren't linked to the thermal quakes — ones that only occurred in the morning.