When the Apollo astronauts went to the Moon, they placed seismometers on the surface. These instruments strikingly revealed that earthquakes occur on the Moon as well as on Earth. In fact, scientists have since identified four types of moonquakes: deep, shallow, thermal, and types caused by meteor impacts.
But a new look at thermal earthquake data recorded by instruments on the Apollo 17 mission revealed a fifth and unexpected type of moonquake; An earthquake originating from the Apollo 17 lunar landing base itself.
During the Apollo 17 mission, scientists calibrated three seismometers to record thermal earthquakes on the Moon. These devices placed on the lunar surface recorded data from October 1976 to May 1977. These types of thermal earthquakes are caused by intense temperature changes that occur on the Moon as it transitions from day to night, which can range from 121 degrees Celsius to -133 degrees Celsius.
Researchers from the California Institute of Technology reanalyzed the data using modern techniques, including machine learning, and determined that thermal earthquakes occur with very precise regularity throughout the day. However, they also found new tremors in the data that were not linked to thermal earthquakes; Only things that happen in the morning…
Researchers triangulated the source of the mysterious tremors and discovered, surprisingly, that they were coming from the Apollo 17 lunar lander base, which was expanding and pulsating as it was heated by the sun each morning. “The signals appear every lunar morning as the sun hits the lander,” Allen Husker, professor of geophysical research and co-author of the new study, said in a statement. “It repeats every five to six minutes for five to seven Earth hours. “They were incredibly regular and repetitive.”
Ultimately, the team determined that these unusual signals originated from the Apollo 17 lander base. When the vehicle warmed up in the morning and started crackling due to heat, the vibrations were detected by nearby seismographs.
Besides being a cool discovery in itself, the team believes that future Moon missions could help them understand how the equipment expands and contracts while on the Moon’s surface. It will be important for the missions to find useful mineral deposits under the surface before returning to the Moon, and perhaps even before starting to work on the Moon base.
“We hope to be able to map underground craters and look for deposits,” Husker added. “There are also certain areas in the craters at the Moon’s South Pole that never see sunlight, they are constantly in shadow. “Since seismic waves travel slower in water, if we could put a few seismometers in there we could look for water ice that might be trapped underground.”
The study was published in JGR Planets.
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