What was on the surface of the young moon went deeper into the satellite, and what was inside — came to light.
Scientists have been discussing for decades the possibility that billions of years ago the Moon «everted» — in a new paper, published in the journal Nature (via Live Science), planetary scientists at the University of Arizona provide their own evidence. The team conducted a series of simulations in which gravitational anomalies on the near side of the Moon are consistent with the presence and location of dense minerals that have been preserved since the first days of the Earth’s natural satellite Planetary scientists have also determined that this «coup» occurred approximately 4.22 billion years ago — shortly after the Moon formed from a piece of the Earth that broke off after a violent collision at the beginning of the solar system.
There is a region on the near side of the Moon that scientists have nicknamed «geochemically strange» — known as the KREEP region, which is rich in specific and unexpected metals such as potassium, rare earth elements, and phosphorus.
The region is intersected by «lunar seas» — large basalt plains formed by volcanic activity and rich in ilmenite (a mineral composed mainly of titanium and iron). The ilmenite is also quite dense, which is surprising given the lower density of the rocks here — it is believed that these minerals once sank on the Moon, while less dense rocks rose to the surface.
The presence of the aforementioned metals and minerals can be explained by geodynamic processes that began shortly after the Moon’s formation. Initially, the satellite was covered by an ocean of molten magma, which cooled to form the crust and mantle — in this scenario, when the magma reaches cooling and crystallization, dense minerals such as ilmenite form in the layer between the crust and mantle, and KREEP elements are concentrated in a liquid reservoir.
It is possible that after the initial plunge, the ilmenites heated up and rose again, tipping over the mantle in the process — this could explain the geochemical oddities of the Moon, but in this scenario, both sets of elements should be distributed more or less evenly.
One explanation cited by planetary scientists is related to the South Pole — Aitken basin on the back of the Moon, which was once formed by a powerful impact. The crater now covers more than a quarter of the satellite’s surface and could «hide» the migration of ilmenite and KREEP.
The researchers realized that the migration should have left clear gravitational traces and created models of the «lunar coup» that produced a clear polygonal pattern of linear gravitational anomalies that coincided with the observations of NASA’s spacecraft.
«Thus, the moon’s gravitational field retains critical information about the lunar mantle rollover, which is considered one of the defining events in the satellite’s early history, but the details have remained unknown until now», — the researchers write.