Photo: charter97.org/Иван Mezhui
Astronomers have been trying to understand the mysteries of the invisible part of the moon.
Planetary scientists found that the differences between the visible and back sides of the moon can be related to the fact that radioactive elements distributed over its mantle is heterogeneous. The results of a study published the scientific journal Nature Geoscience.
“On the lunar surface traces of geological processes that occur in the early days of the Solar system. In particular, on its visible side there are regions with uniquely high concentration of uranium and thorium. If we know how did this surplus, we will understand, as there is a Moon and what conditions prevailed on Earth at that time,” said one of the study’s authors, a geologist from the Institute of Technology, Tokyo (Japan) Mathieu Lanoville.
In contrast to the relatively flat visible sides, the reverse side of the moon is covered with many hills, clefts and craters. Measurements of the force of gravity of our satellite show that the visible half invisible heavier, and the craters on the surface of the latter is deeper, and the lunar crust is relatively thinner.
Astronomers quite a long time trying to understand what it involves. In particular, some planetary scientists believe, almost immediately after the formation of the moon on its surface fell one or a few “germs” of planets. This can explain the unusual isotopic composition of the moon, and the differences between the hemispheres of the satellite.
Laneville and his colleagues have found a simple and plausible explanation for these differences. They figured out how they were arranged the mantle of the moon of the newborn immediately after the collision of its progenitor, theis, with the Earth.
Planetary scientists suggest that the traces of the first stages in the formation of the moon can be found in special rocks on its surface, which geologists call KREEP. These minerals are especially rich in potassium (K), rare earth elements (REE) and phosphorus (P). Dozens of fragments of these rocks that are formed from 4.3 to 3.9 billion years ago, brought the expedition of the Apollo program.
The main unusual feature of KREEP-sediments lies in the fact that in these rocks is about 700 times more uranium and thorium than in primitive asteroids are chondrites, which are composed of primary matter of the Solar system. This gave geologists the idea that radioactive substances and the heat generated by them played an important role in the formation of the moon and geologic processes in its interior.
Following this idea, Lanoville and his team tried to reproduce in the experiments the process of formation of KREEP and all lunar rocks in General. To do this, scientists have created artificial analogue of the samples of the two terrestrial lava volcanoes.
The experiments showed that concentrations of KREEP in the mantle really was to play an important role in the process of formation of the subsurface of the moon, warming them and maintaining in the molten state for much longer than geologists originally thought. Given that the visible side of our satellite these rocks much more, it can be concluded that it is frozen later than the opposite hemisphere of the moon.
Such differences in the behavior of the mantle and crust of the moon, according to the researchers, explain why the shape of her hemispheres so different. In particular, their calculations indicate that the depths of the visible side of the moon produced from approximately 4 to 13 times more magma than the other half. The result is a vast lunar “seas” — the footprints of a gigantic lava flows and thicker bark, which is on the other side of the moon, conclude the authors.