Half the Month Is Warmer Than All the Other Months

Research indicates that the moon’s gravitational pull suggests a warm, dense interior, hinting at structural irregularities beneath its surface.

The distinct appearance of the moon’s near side compared to its far side has intrigued observers since time immemorial. However, it raises questions about whether these differences provide insights into the deeper layers of the moon, as stated by Ryan Park from NASA’s Jet Propulsion Laboratory in California. Together with his colleagues, he is utilizing data from NASA’s GRAIL spacecraft to investigate.

The GRAIL mission gathered crucial data on the moon’s gravitational variations during 2011 and 2012, while two spacecraft orbited the lunar body. Since the gravity field is reflective of physical characteristics, researchers were able to analyze how it deforms based on both the moon’s shape and Earth’s tidal forces.

Despite this, the variations in the gravity field could not solely be accounted for by the observable features of the moon’s surface. Scientists contemplated the possibility of a heterogeneous interior. Previous findings suggested that the moon’s near side would exhibit more deformation compared to the far side due to Earth’s gravitational influence, as noted by Jeffrey Andrews-Hanna from the University of Arizona. This recent research validates that assertion, enabling a deeper understanding of the moon’s structure.

Using GRAIL data, Park and the team calculated that the moon’s susceptibility to Earth’s gravitational pull was 72% higher than what would be expected if the moon’s interior were entirely uniform.

The research team examined various factors contributing to this anomaly, including the moon’s chemical makeup. However, the model that closely aligned with the observed data was one indicating a temperature variation, suggesting that the moon’s interior is warmer than the far side.

Sean Solomon from Columbia University in New York noted that this model aligns with existing knowledge about the moon’s volcanic history and the distribution of radioactive elements, such as uranium and thorium, on its surface.

While the exact reasons for the moon’s irregular interior remain uncertain, Park suggests that some of these variations may result from its turbulent history of impacts with other celestial bodies. Moving forward, he and his team aim to utilize seismic data from lunar quakes to further explore the moon’s internal structure. These data will be gathered by the Far Side Earthquake Suite, which NASA plans to deploy in 2026.