Our Moon May Have Turned 'Inside Out’ During Its Formation 4 Billion Years Ago, Study Finds

As the Earth cooled from its earlier molten state, the densest materials such as iron and nickel sank to its middle. This is why our planet’s crust is about four times less dense than its core. While this is standard procedure, our delinquent lunar neighbour does not care for these rules too much, it turns out.

The Moon’s surface sports some bizarre anomalies that have kept scientists at their wits’ end. On its near side exists a region of the Moon called the KREEP Terrane. Named after an acronym of the elements found in the place (K for Potassium, REE for rare-earth elements and P for Phosphorus), this lunar section also lies alongside a volcanic spot that is riddled with an overabundance of heavy elements such as titanium, iron and ilmenite.

The problem is that these heavy elements lie on top of rocks that are far lighter, which really doesn’t make sense. We know that, similar to the Earth, the Moon too had a liquid mantle at one point in its adolescent past, which would have allowed these dense rocks to filter through the less dense bits to sink to the bottom. So, why on Moon are they on the surface?!

After decades of head-scratching, a new study has offered one, almost unreal explanation: the Moon simply turned inside out!

Through meticulous analysis of gravitational anomalies and the reconstruction of lunar geological processes, the researchers reckon that as a young Moon began cooling down, denser materials such as ilmenites concentrated between its crust and mantle. Meanwhile, the KREEP elements bunched up in a liquid reservoir in the region.

This new model has been verified by gravity information collected by NASA’s lunar gravity mapping satellite GRAIL, which revealed that this overturn took place at least 4.22 billion years ago. The discovery sheds light on the complex interplay of geological processes that shaped the Moon's composition billions of years ago.

These findings not only provide a deeper understanding of lunar evolution but also offer insights into the broader processes shaping planetary bodies across the cosmos.

The findings of this research have been published in Nature Geoscience and can be accessed here.

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