The moon is shrinking.  What are the implications for astronauts?

What is the diameter of the moon? If you want to provide the size with metric accuracy, you will face a difficult task. Not only because our natural satellite is not a perfect field. There is also another problem. It turns out that the moon is shrinking.

Yes, your eyes are not deceiving you. Scientists have reached this conclusion, which is that the size of the moon is decreasing. The moon is not the only celestial body that undergoes such a process. The same applies to mercury. The reason is the slow cooling of the interior of these celestial bodies. It is a process that occurs on a geological scale, over hundreds of millions of years.

In theory, it should not matter to us whether the Moon was a little larger and is now a little smaller. Because “back in the day” was the time of the dinosaurs. Also, the change in the distance of the Moon from the Earth did not cause any disasters on Earth during the existence of our civilization. In the end, the day will be much longer because of this, but that won't be our problem. But what about deflation?

The circumference of the moon is decreasing. About 45 meters in several hundred million years

Changing the Moon's circumference by several tens of meters does not seem to be a big change. Although our natural satellite is smaller than Earth, it has an equatorial circumference of about 11,000 km. What could a 100,000 percent change cause? It turns out a lot.

The Moon's crust is not elastic and the shrinkage of the Earth's surface causes stress. Cracks form in the Earth's crust, which is clearly visible in images taken by Earth's orbital vehicles. From its appearance, in 2019 it was already deduced how dynamic this phenomenon is. This information, supported by data from seismometers left on the surface by Apollo astronauts, has now allowed further conclusions.


Lunar slope, a place formed as a result of seismic activity associated with the contraction of the Moon.

Lunarquakes are the result of the contraction of the Moon. Their source is directly from new emerging cracks, but also, as on Earth in the case of tectonic plates, the overlapping of previously separated parts of the crust.

Of course, it is not only the contraction of the Moon that causes earthquakes, but also tidal effects from the Earth. However, the latter mainly causes deep and not very strong shocks. The strongest force recorded corresponds to a force of about 5.5 on the Richter scale, so it would have been felt strongly on the ground.

How can lunar earthquakes threaten astronauts?

Good. We have earthquakes on the Moon, as well as on Mars, and perhaps even on Mercury. This would mainly be a scientific curiosity, if not because we want to colonize the Moon in the not too distant future. The places where seismic activity is particularly strong are the southern regions of the Earth. The strongest lunar earthquakes on record were associated with the shelf near De Gerlach crater, 60 km from the Moon's south pole. These are the areas where Artemis III astronauts would like to go in the future. In the video below, the potential landing sites coincide with the locations of earthquakes from several decades ago.

Of course, there is nothing to fear in the short term, but who knows if an unlucky lunar earthquake will occur during people's stay on the moon. Thus, for the many problems related to the construction of human lunar habitats, there is a further need to ensure resistance to the possible consequences of earthquakes. On the ground, construction leakage wouldn't be a problem. On the moon it could be a matter of life or death. And not just because of the shocks, but because of what they can cause in the long term.

Choosing a place for long-term residence on the moon is not easy. It is necessary to conduct seismic studies on our natural satellite to determine where the quietest place is.

So far, statistics on lunar earthquakes, especially those whose sources are located close to the surface, show how serious the problem is. On Earth, such an earthquake lasts for a short time, and aftershocks may occur, but they are not long-lasting. However, on the Moon, the duration of an earthquake is measured in hours. If a particular residential or technical structure is to be resistant to damage, it must withstand long-term shocks. Its structure must be resistant to the earthquake itself, but also to landslides caused by earthquakes.

The latter could be very dangerous, as explained by Nicholas Schmer, co-author of a research paper proving the moon's contraction and the connection of this process with shallow seismic activity. He points out that the surface of the Moon, which is constantly bombarded by asteroids, consists of highly processed materials ranging in size from microscopic particles to rocks. However, this material is not well bonded which poses a risk. In the area of ​​Shackleton Crater, roughly at the Moon's south pole, it is particularly high.

Source: NASA, information. king

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