Tucson Standard

A recent study published in Nature Geoscience sheds light on the evolution of the moon's interior, offering new insights into its formation and structure. The research, conducted by scientists from the University of Arizona Lunar and Planetary Laboratory (LPL), explores how dense minerals like ilmenite sank into the lunar interior after forming a global magma ocean.

"Because these heavy minerals are denser than the mantle underneath, it creates a gravitational instability, and you would expect this layer to sink deeper into the moon's interior," explained Weigang Liang, who led the research as part of his doctoral work at LPL.

The study draws on rock samples collected by Apollo astronauts over 50 years ago and combines them with theoretical models. These samples revealed high concentrations of titanium in basaltic lava rocks found primarily on the moon's nearside. However, their origin remained a mystery until now.

"Our moon literally turned itself inside out," said co-author Jeff Andrews-Hanna. "But there has been little physical evidence to shed light on the exact sequence of events during this critical phase of lunar history."

The researchers suggest that after forming beneath the crust, ilmenite-rich material migrated to the near side due to gravitational forces and eventually sank into the interior in sheetlike slabs. This process left behind a network of dense material below the crust.

"When we saw those model predictions, it was like a lightbulb went on," said Andrews-Hanna. "We see the exact same pattern when we look at subtle variations in the moon’s gravity field."

Using data from NASA's GRAIL mission, which orbited the moon between 2011 and 2012, researchers compared simulations with detected linear gravity anomalies surrounding dark volcanic regions known as mare. Their findings align with predictions about how ilmenite materials moved within the lunar interior.

"Our analyses show that models and data are telling one remarkably consistent story," Liang noted. The timing of these events is also constrained by cross-cutting relationships with impact basins formed more than 4 billion years ago.

"The vestiges of early lunar evolution are present below today's crust," Adrien Broquet commented. Future missions could further explore these structures using seismic networks for better understanding.

Liang added: "When Artemis astronauts eventually land on our neighbor again for exploration purposes - we will have an entirely different understanding than during Apollo times."