Unusual Events on the Moon: Our Team is Left Scratching Their Heads

A recent study by NASA has uncovered an unexpected and curious fact about the moon’s deep interior.

Utilizing data from the Grail Spacecraft, researchers found that the side of the moon facing Earth is “bending” more than the far side, indicating a remarkably unstable internal structure between the two hemispheres.

“We have long believed the moon to be spherically symmetrical deep down, so encountering clear evidence to the contrary was both surprising and challenging,” said Dr. Ryan Park, the study’s lead author and head of the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory, as reported by BBC Science Focus.

Published in Nature, the study reveals that the moon visible from Earth deforms more significantly under the gravitational influence of Earth than on its far side, measured using ultra-precision gravity techniques.

This finding relies on a metric known as the “Love number,” which quantifies the extent to which a celestial body deforms due to tidal forces. After nearly a decade of intricate calculations involving millions of parameters, the team found that the Love number was approximately 72% greater than what would be expected for a symmetrically spherical moon.

“When we first calculated higher Love numbers than anticipated, our team was genuinely perplexed,” Park noted. However, the calculations confirmed it: the moon exhibits instability both internally and externally.

The cause? The mantle on the near side is warmer and less rigid compared to the far side, attributed to radioactive heating early in the moon’s history.

This phenomenon is likely due to ancient geological activities. The near side contains a significantly higher concentration of radioactive materials, including up to 10 times more thorium. These elements emit heat as they decay.

Billion years ago, this heat led to the formation of pockets of partially melted rock, sparking massive volcanic eruptions. These eruptions resurfaced the near side with dark plains known as “Mare,” while the far side remained rugged and cratered.

This study generates the most comprehensive gravity map of the moon to date. Future missions, such as NASA’s Artemis program, aim to enhance navigation on the lunar surface and aid in developing lunar navigation systems.

Looking to other regions of the solar system, Park plans to apply a similar methodology to investigate the metal-rich asteroid Psyche and the icy moons of Jupiter, particularly Europa.

“The most astonishing aspect was how pronounced the asymmetry was,” Park added. “This compelled us to examine the intricacies of the moon’s thermal and structural evolution, ultimately yielding new insights into how the moon—and potentially other celestial bodies—develop internal disparities over billions of years.”

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About our experts

Ryan Park is the supervisor of the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory in Southern California. His research has been featured in prestigious journals, including Science, Journal of Astrophysics, and Nature.