14-05-2025
NASA Just Found the Moon Is Uneven—What We Know So Far
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The moon's insides are crooked thanks to the near side being some 306 degrees Fahrenheit hotter at depth than its counterpart on the lunar far side.
This is the conclusion of an international team of researchers based on gravitational data collected by a pair of NASA spacecraft dubbed "Ebb" and "Flow."
The findings could help explain differences seen in the moon's surface geology, with the near side being darker and dominated by lava flows and the far side more rugged.
The thermal differences, the researchers wrote in their paper, "formed surface mare regions 3–4 billion years ago—and could influence the spatial distribution of deep moonquakes."
(Mare is the name given to the large, dark plains of basalt on the moon that were formed as the result of volcanism and lava flows.)
An artist's cross-section of the moon.
An artist's cross-section of the moon.
AlexLMX/iStock / Getty Images Plus
In their study, aerospace engineer Ryan Park of NASA's Jet Propulsion Laboratory and colleagues analysed data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, which launched in 2011.
Flying in tandem around the moon, GRAIL's twin spacecraft not only mapped out variations in the lunar gravitational field, but in doing so, created the highest-resolution map of any celestial body made to date.
"As the two spacecraft flew over areas of increasing gravity, the probes moved slightly toward and away from each other, while an instrument measured changes in their relative velocity, providing key information on the moon's gravitational field," NASA said.
The researchers went a step further and used this data to map the moon's gravitational response to how it orbits around the Earth, which allowed them to learn more about the internal structure of the moon.
The analysis revealed that the mantle beneath the near versus the far side of the moon has a difference in its ability to deform—one of about 2–3 percent.
Modeling the moon's internal structure, the researchers determined that this differential could be explained if the mantle on the near side of the moon was between 180–360 degrees Fahrenheit warmer than on the far side.
Park and colleagues believe that this temperature difference could be sustained by the radioactive decay of elements like thorium and titanium on the moon's Earth-facing side—a remnant of the volcanic activity that formed the near side surface 3–4 billion years ago.
The success of the method used in the study—properly known as "tidal tomography"—could pave the way to similar analyses of other cosmic bodies, the team notes.
"In the future, these techniques can be applied to other planetary objects showing pronounced low-order surface variations, such as Mars, Enceladus and Ganymede," they wrote.
They concluded: "Because tidal tomography does not require a landed spacecraft, unlike seismology, it should be an important component of future missions that include an orbiter around the target body."
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Reference
Park, R. S., Berne, A., Konopliv, A. S., Keane, J. T., Matsuyama, I., Nimmo, F., Rovira-Navarro, M., Panning, M. P., Simons, M., Stevenson, D. J., & Weber, R. C. (2025). Thermal asymmetry in the Moon's mantle inferred from monthly tidal response. Nature.