Moon’s dramatic flip inside out puzzles scientists

A fascinating discovery has shed light on a period when the Moon underwent a dramatic transformation, essentially inverting itself from the inside out. This finding comes from a recent publication by researchers at the University of Arizona’s Lunar and Planetary Laboratory, focusing on the turbulent history of the lunar interior. The study, featured in Nature Geoscience, delves into the Moon’s chaotic development over time.

Jeff Andrews-Hanna, an associate professor at the Lunar and Planetary Laboratory and co-author of the study, shared in a press release, “Our moon has essentially turned itself inside out. However, pinning down the specifics of this significant chapter in lunar history has been challenging, with little physical evidence and considerable debate over the details of these events.”

The Origin of the Moon:
It is widely believed among scientists that the Moon came into existence around 4.5 billion years ago, following a colossal collision between Earth and a smaller celestial body. This catastrophic event ejected molten rock into space, which eventually began orbiting Earth. Over time, this debris cooled and solidified to form the Moon.

Analysis of lunar rocks collected by Apollo astronauts has provided insights into the Moon’s ancient past. Subsequent satellite observations revealed that volcanic rocks are predominantly found on the Moon’s near side.

A novel model developed by the University of Arizona researchers has offered explanations for this distribution. In the early stages of the Moon’s formation, it was enveloped by a global ocean of magma. As this molten rock solidified, it gave rise to the Moon’s mantle and crust.

The team’s computer simulations demonstrated that as the magma beneath the crust crystallized, it formed dense minerals such as ilmenite, rich in titanium and iron. “These heavier minerals, being denser than the underlying mantle, would likely create a gravitational instability, causing this layer to plunge deeper into the Moon’s interior,” explained Weigang Liang, the lead researcher of the study during his PhD at the Lunar and Planetary Laboratory.

This dense material eventually descended into the Moon’s interior, where it melted and blended with the mantle. Over time, it resurfaced in the form of titanium-rich lava flows that are now visible on the Moon’s surface.

Through their research, the team discovered that the Moon’s gravity field could be used to trace the distribution of ilmenite remnants, which had descended into the lunar mantle. This analysis was supported by data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) lunar satellite.

Liang noted, “Our findings reveal a strikingly coherent narrative. The migration of ilmenite materials to the Moon’s near side and their descent into the interior formed sheetlike structures, creating anomalies in the Moon’s gravitational field observed by GRAIL.”

Based on their findings, the researchers estimate that the layer enriched with ilmenite sank into the Moon’s interior over 4.22 billion years ago.