The moon shrinks, it causes moonquakes

As the inner part of the moon cools down, over the past several hundred million years it has shrunk to 50 meters, and new folds, ditches, ditches and fractures have appeared on its surface.

Launched by NASA on June 18, 2009, the lunar orbital probe (LRO) continues to be used to obtain a large amount of valuable scientific information and new discoveries.


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The current elliptical orbit is LRO (40x199 km), with the nearest point of orbit at the South Pole.



According to NASA, the LRO is a modular LROC camera (Lunar Reconnaissance Orbiter Camera) - the main optical camera for taking photographs of the lunar surface with a resolution of up to half a meter.

LROC consists of three cameras: a low-resolution camera (WAC) and two high-resolution cameras (NAC), the first of which is intended for obtaining general terrain plans, and the other two are for high-resolution photographs.

Billions of years ago, on the Moon, huge pools formed in their areas, which we now call Seas.

Lunar seas are vast lowlands filled with basalt lava. Initially, these formations were considered ordinary seas. Subsequently, when it was refuted, the name was not changed. Lunar seas occupy about 40% of the visible area of ​​the moon.



Studies of these formations were carried out by many scientists, who came to the conclusion that all these basins have long been dead, because according to their calculations, the last geological activity occurred on the moon long before dinosaurs lived on Earth.

However, a detailed computer analysis of more than 12,000 images from the LRO probe gave quite unexpected results, which show that at least one of the studied surface areas of the Moon recently had weak geological activity, new cracks appeared on the surface and displacements of the upper layers were recorded.



Moreover, some of these cracks and faults go through existing craters, that is, these deformations were formed after the meteorites hit the surface of the Moon at this place.

But scientists and astronomers have several ways to determine the age of impact craters on the Moon, including by analyzing images with LRO (the lighter, the younger), according to the degree of damage and the sequence of formation.

After all, the appearance of each crater is accompanied by the emergence around it of a wide area with a modified reflection coefficient. Sometimes (in 84% of cases) the reflectivity of such an area was increased by several percent, sometimes lowered, there were also recorded cases of areas around the craters with both high and low reflectivity, since when a crater occurs, the lunar rock ejected from it is scattered around.

Regolith, which forms the basis of the lunar surface, is a loose, very porous, to some extent sintered soil. It consists of fragments of igneous rocks, minerals, glass and meteorites. It has a thickness of up to several tens of meters. According to estimates made by astronomers, the upper two centimeters of this regolith, having a particularly high porosity (up to 90%), are responsible for the appearance of areas with reduced reflectivity, and increased reflectivity occurs when deeper and less friable rocks are ejected from the crater. After studying the process of formation of lunar craters and the secondary processes accompanying it, the scientists came to the conclusion that the mixing of the upper several centimeters of regolith formed this layer for 80 thousand years.

Chronological scale of the geology of the moon.

By the way, in our time there are new craters on the moon.



This discovery gives us a new understanding of the understanding of the geology of the moon, as the actively changing world in the present.

The photographs of the LRO probe clearly show the folds on the surface, the curved contours of the hills and the shallow long serpentine trenches that were formed during the compression of the internal structures of the Moon during their cooling.



Previous studies of the lunar surface also recorded similar deformations, but only in the high-altitude mountain regions of the moon, in areas of the Moray, this phenomenon was recorded for the first time.

The difference between the lowest point and the highest point on the moon is 16 kilometers.



Moon topography data obtained using the LRO probe:



Using the LRO probe, NASA conducted a detailed study on the presence of surface deformations in the Sea of ​​Cold near the North Pole of the Moon, numerous surface formations were recorded - ground breaks, folds on the surface, ornate curved contours of hills and ridges.



According to NASA researchers, some of the formations appeared quite a long time ago, about a billion years ago, while some of these deformations are much younger — no older than 40 million years, which is “recently” from a geological point of view.

Although previous studies have shown that all geological activity in the seas ceased about 1.2 billion years ago.

On the Moon, as on Earth, there are various tectonic phenomena and processes that are caused by moonquakes.

The structure of the Earth and the Moon in the pressure scale:



The planetary feature of the deep structure of the Moon is its division into a powerful rigid, cold outer sphere and a heated, partially melted and plastic inner region.

On the surface of the moon, the temperature varies from + 125 ° C during the day to -170 ° C at night, while the temperature of the rocks lying at a depth of 1 m is constant and equal to −35 ° C.



The average thickness of the moon's crust is 68 km, varying from 0 km under the lunar sea of ​​Crises to 107 km in the northern part of Korolev crater on the back side.



Under the crust there is a mantle and a small core of iron sulphide (radius of approximately 340 km and a mass of 2% of the mass of the moon).

The temperature in the core, presumably, ranges from 1327 ° C to 1427 ° C. The core heats the inner layer of the molten mantle, but it is not hot enough to warm the surface.

An example of the studied geological composition and characteristics of the upper part of the lunar surface, which are deformed under the influence of moonquakes:



The moon has no tectonic (lithospheric) plates, and all endogenous geological processes occur as a result of a slow internal process of heat loss, which lasts almost 4.5 billion years.

Thus, the lunar tectonic activity is probably due to the fact that the moon continues to shrivel like raisins, since its interior is cooled and compressed. However, unlike the flexible peel on the grapes, the lunar crust is fragile, which leads to its rupture and deformation on the surface.

The moon cools down and shrinks, it becomes denser, and its surface shrinks and cracks more and more, new deformations are created on it:









Here are the trenches (grabens) that were formed during the sinking of parts of the surface of the moon that were recently fixed by the LRO probe:



As the moonquakes and contractions occurred below the surface of the moon in the area of ​​the Cold Sea, new fractures, trenches and soil folds appeared at the top. The longest of them extend to a distance of 400 kilometers and can rise to a height of 340 meters.







How many moonquakes due to such a compression process took place recently on the moon?

It was here that NASA was able to combine new data from the LRO probe with photographs of lunar surface faults and data from seismometers on the four landing sites of the Apollo missions on the Moon, which recorded 28 small moon shocks from 1969 to 1977, with a magnitude of 1, 5 to 5 on the Richter scale.



Some of these moonquakes could theoretically result from the activity of lunar faults, but the location and depth of the sources of these moonquakes were uncertain.

The results of NASA's new research led to an improvement in the assessment of the epicenters of minor moonquakes, finding that eight of them were 30 km away from the young lunar faults, which were formed under the influence of the stress that arose when the lunar crust contracted once again.

Seven moonquakes within a radius of about 60 km from these faults, and they occurred when the moon was at the furthest point in its orbit from Earth, and some parts of the moon are experiencing the greatest stress from the gravitational pull of the Earth.



Current near-surface stress state of the moon (current near-surface state of stress on the surface of the moon):



Thus, seismic data, which were obtained more than 40 years ago, have now been further interpreted and helped to confirm that the Moon continues to be tectonically active, which will need to be taken into account in subsequent research expeditions.



NASA is already ready to install a new network of seismometers on the lunar surface to learn more about the inner part of the moon and determine how dangerous moonquakes are. Also, with the help of this project, it is planned to study meteorite impacts and other events that can cause moonquakes, but with excellent signatures from moonquakes that occur during the displacement of faults. The timing of this project has not yet been determined.