Scientists have found the cause of strange repeated tremors on the Moon

In the 1970s, astronauts placed three seismographs on the lunar surface to collect data between October 1976 and May 1977. In the new research Scientists re-examined the instrument data and finally found the cause of some of the repeated tremors - they came from the Apollo 17 lander, which landed on the moon in 1972. However, first things first.

When earthquakes occur on Earth, waves of energy travel in all directions. By measuring them at several places on the surface, scientists can create a map of the subsurface. Because rocks and liquids on Earth have different densities, waves move through them at different speeds, allowing geologists to figure out what type of material the energy is passing through. This is called seismic tomography.

Similarly, the American Apollo program placed a number of seismographs on the Moon to similarly learn about its structure. By analyzing this data, scientists obtained the first data on the internal structure of the satellite, including the presence of a core with a diameter of about 500 kilometers, which is much less dense than that of the Earth.

It is believed that lunar earthquakes are not caused by the movements of tectonic plates, as on Earth. Instead, the main driving factor is the Earth's gravity, which causes strong tidal forces, as if splitting the Moon apart. Other types of moonquakes recorded by Apollo seismographs were likely caused by meteorite impacts. But the systematically repeating moonquakes, which occurred as if by clockwork, were more difficult to explain using the available data.

In a new study, scientists from the California Institute of Technology used machine learning to analysis of data from three seismographs placed by the Apollo 17 crew several hundred meters from their base. Researchers discoveredthat some seismic activity occurs regularly, every lunar day, when the surface of the satellite begins to cool. And in a similar way, unusual repeating signals were observed on a lunar morning when the sun rose over the satellite.

What a surprise the scientists were when, after analyzing all the data, they came to the conclusion that the tremors that the seismographs picked up came from the Apollo 17 descent vehicle itself. When its casing heated up in the morning and began to expand, the creaking vibrations were read by instruments as some kind of tremors. And on a lunar night, the module cooled down and the metal could shrink a little, which was also recorded by geological sensors.

The institute's team thinks this is a cool discovery in itself because it could help future lunar missions understand how equipment expands and contracts on the lunar surface - before we return to the satellite or perhaps even start working on lunar base.

What is noteworthy is that the Indian lander Vikram, which recently landed on the Moon, is also equipped with a seismograph. And before you go to hibernation, He recorded some movements under the surface of the satellite. Their reason is still unclear.