Why the visible hemisphere of the moon is heavier than the invisible, scientists have found out

(ORDO NEWS) — Paleologists have found that the differences in the mineral and chemical composition of the rocks of the visible and dark hemispheres of the Moon are due to the fact that a large asteroid fell on its south pole shortly after its formation. The conclusions of the scientists were published by the scientific journal Nature Geoscience.

“Our calculations indicate that the fall of a large asteroid on the south pole of the Moon in the region of the South Pole – Aitken basin should have” mixed “lunar basalts in a special way and moved them towards the visible hemisphere of the Moon.

If our theory is correct, then in the rocks that the lunar rover “Chang’e-5” collected in the Ocean of Storms, there will be a lot of titanium and rare earth metals, “the scientists write.

The far side of the Moon, in contrast to its relatively “flat” visible side, is covered with many hills, crevasses and craters. Measurements show that the visible part of the Moon is noticeably heavier, invisible, and the rocks of both halves of the satellite differ markedly from each other in chemical, isotopic and mineral composition.

A group of planetary scientists led by Ding Ming, associate professor at the Macau University of Science and Technology (China), found that all these differences arose after a large asteroid fell to the south pole of the Moon in the early epochs of its existence.

Scientists came to this conclusion when analyzing the data collected by the Chinese lunar rover “Yuytu-2” and orbital probes in the circumpolar regions.

Geological history of the birth of the Moon

The data show that the mantle rocks in the vicinity of the so-called South Pole – Aitken basin, the largest crater on the lunar surface with a diameter of 2,400 km, significantly differed in composition and appearance from the neighboring regions of the Earth’s satellite.

In particular, they contained unusually low levels of rare earth metals, as well as ilmenite and other rocks containing large amounts of titanium and thorium.

At the same time, scientists found that the highest concentrations of these elements and rocks were observed on the opposite side of the moon, in the northwestern regions of its visible hemisphere.

This prompted Ding Ming and her colleagues to think that both of these anomalies are associated with the same event – the fall of a giant asteroid, after which the South Pole – Aitken basin emerged. This happened about 4.3 billion years ago.

Guided by these considerations, planetary scientists calculated the consequences of the fall of a large asteroid on the Moon in the last moments of its formation, when its bowels were already partially frozen.

The computer model they created confirmed that the collision of the Moon and even relatively small asteroids should have re-melted the bowels of the Earth’s satellite and generated significant differences in the distribution of those rocks of its mantle, which contain titanium, thorium and rare earth metals.

Traces of this “mixing” of the lunar interior, according to Ding Ming and her colleagues, should be contained in rock samples from the lunar Ocean of Storms, which were delivered to Earth last December by the Chang’e-5 mission.

Scientists hope that through their study they will be able to confirm this theory or find another explanation for the differences in the mineral, chemical and isotopic composition of the visible and reverse hemispheres of the Moon.


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