The Moon was geologically active billions of years ago, experiencing quakes, volcanic eruptions, and outgassing. While it has been geologically inert for a long time now, it still experiences small seismic events due to tidal flexing and temperature variations, known as “moonquakes.” Using seismometers placed on the lunar surface by the Apollo missions, researchers from the California Institute of Technology (Caltech) recently reexamined the seismic data with a machine-learning model.
The study, led by Francesco Civilini, a postdoc graduate from Caltech, revealed that moonquakes occur with precise regularity, coinciding with the Sun rising to its peak position in the sky and then slowly setting. Unlike tidal flexing in the Moon’s interior, moonquakes result from temperature changes in the lunar crust. The heat from the Sun is not retained in the airless environment on the Moon, leading to drastic temperature variations causing the crust to expand and contract rapidly, triggering small seismic events.
Civilini and his team reanalyzed lunar seismic data collected over a period of eight months (October 1976 to May 1977) with the help of a machine-learning model. Their analysis showed that thermal quakes occur with precise regularity every afternoon as the Sun leaves its peak position in the sky and the surface begins to cool rapidly. The model also detected seismic signatures in the morning that looked different from evening quakes.
The researchers found that the morning tremors were coming a few hundred meters away from seismometers – from the Apollo 17 lunar lander itself. As sunlight reached the vehicle every morning, its surface would expand, causing vibrations in the ground that were detected by the seismic array. The data could have significant implications for future missions to the Moon, providing vital data that could inform the design of future landers and equipment.
Seismic activity is a good way to probe the interiors of celestial bodies, which can be used to infer the interior structures of celestial bodies and locate materials underground. While there is no plate tectonics or volcanic activity on the Moon, researchers still have many questions about the Moon’s internal structure, and the insights gained from this study could help design future experiments and missions.
The findings from the research could impact the structure of future lunar bases, such as the Artemis Base Camp, the International Lunar Research Station (ILRS), and ESA’s proposed Moon Village. The data could also inform the use of composite materials instead of alloys to avoid triggering local quakes.