Nobody knows what made the gargantuan crater on the dark side of the moon

Billions of years ago, something slammed into the The dark side of the moon and dug a very, very big hole. Extending 2,500 km wide and 13 km deep, the South-Aitken Pole BasinThe terrifying hole known to the earthlings is the oldest and deepest lunar crater and one of the largest craters in the solar system.

For decades, researchers have suspected the gigantic basin to be created by a frontal collision with a very large meteor. Such an impact would have torn the moon's crust and pieces of lunar mantle scattered over the surface of the crater, providing a rare glimpse of the actual composition of the moon. (Divulgacher: This is not cheese.This theory gained credibility at the beginning of the year, when the Chinese robot Yutu-2 settled at the bottom of the crater on board. the LG Chang & # 39; e 4 in January, discovered traces of minerals that seemed to come from the lunar mantle.

Now, however, a study published August 19 in the newspaper Geophysical Research Letters throws these results – and the story behind the crater – into question. After analyzing the minerals in six soil plots located at the bottom of the South Pole-Aitken Basin, a team of researchers says the crater composition is fully crusted and there is no coat, suggesting that whatever the impact that it opened the crater billions of years ago hard enough to spray the bowels of the moon on the surface.

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"We do not see the mantle materials at the landing site as expected," said co-author of the study, Hao Zhang, scientist in planetary sciences at the University of Geosciences China, said in a statement. These results virtually exclude any direct collision with a high-speed meteor and raise the following question: what created the largest crater on the moon, if not a frontal strike?

Illuminate the dark side

In their new study, researchers used a technique called reflection spectroscopy identify specific minerals in the lunar soil depending on how the grains reflect visible and near-infrared light.

Using onboard equipment on the Yutu 2 rover, the team performed reflectance tests on six floor plates during the first two days following Chang & # 's landing. 39; e 4, venturing about 54 meters from the LG. Using a database that identifies lunar minerals based on a variety of factors, including size, reflectance, and degradation due to solar wind – the team estimated the mineral concentration in each of the plots.

A crystalline rock called plagioclase was by far the most abundant mineral in each sample, accounting for 56% to 72% of crater composition, the researchers wrote. Formed as the primordial oceans of cold lava, plagioclase is extremely common in the crusts of the earth and the moon, but it is less abundant in their coats. Although the team detected in the crust of other minerals more common in the lunar mantle, such as olivine, these rocks constituted a too small fraction of the soil samples to suggest that they were not present. a part of the mantle had crossed the crust.

This mineral composition complicates the theory that a giant high-speed meteor would have created the South-Aitken Pole basin billions of years ago, since such an impact would almost certainly have scattered mantle pieces on the lunar surface.

So what created the crater? The researchers did not speculate in the new study. However, previous research suggested that a renegade space rocker was still the culprit, but the shot might not have been so direct. A study published in 2012 in the journal Science argued that a meteor moving slightly slower could have hit the back of the moon at an angle of about 30 degrees and create a crater of sufficient size never disturbing the moon's mantle . However, these researchers only had simulations to continue.

At the very least, new research suggests that there is still much to explore in the South Aitken Pole Basin before an answer becomes apparent. We see each other on the dark side of the moon.

Originally published on Science live.