NASA’s new gravitational map of the Moon reveals why its two sides are so different, shedding light on ancient volcanic activity deep within its interior.
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| NASA’s most detailed gravity map yet reveals deep structural differences between the Moon’s nearside and farside, driven by ancient volcanic processes. Image: NASA |
PASADENA, USA – May 17, 2025:
A groundbreaking NASA study has finally unveiled the reason behind the striking differences between the two sides of the Moon—the familiar face visible from Earth and the mysterious farside that always remains hidden.
Using data from the GRAIL mission (Gravity Recovery and Interior Laboratory), researchers developed the most precise gravitational map of the Moon to date. Their findings, published in the journal Nature, reveal a deep asymmetry in the lunar interior, linked to ancient volcanic activity that reshaped the Moon’s nearside billions of years ago.
“Our study shows that the Moon's interior is not uniform: the side facing Earth – the nearside – is warmer and more geologically active deep down than the farside,” said Ryan Park, lead author and supervisor at NASA’s Jet Propulsion Laboratory.
The Moon’s nearside is dotted with vast basalt plains, known as mare, formed by volcanic eruptions. In contrast, the farside remains rugged and mountainous, with far fewer smooth plains. The study points to intense early volcanism on the nearside, which concentrated radioactive, heat-producing elements—such as thorium and titanium—beneath the surface. These elements may still influence the Moon’s internal heat distribution today.
Researchers found that the nearside mantle is 180–360°F (100–200°C) hotter than the farside, based on subtle movements known as tidal deformation—flexing caused by Earth’s gravitational pull. This discovery indicates major compositional differences in the mantle, the geological layer between the crust and the core, which constitutes around 80% of the Moon’s mass.
“The detected asymmetry in the mantle matches the surface geology,” said Alex Berne, a Caltech scientist and study co-author. “It suggests that ancient volcanic processes are still influencing the Moon's evolution today.”
The research team analyzed data from the twin GRAIL spacecraft, Ebb and Flow, which orbited the Moon from 2011 to 2012. Their work not only enhances scientific understanding of lunar formation but also has practical applications.
“This enhanced gravity map is critical for future lunar missions,” Park noted. “It lays the foundation for developing lunar Positioning, Navigation and Timing (PNT) systems, improving navigation safety for spacecraft and surface explorers.”
Beyond the Moon, the method used to assess lunar gravity could be applied to icy moons like Enceladus and Ganymede, offering a roadmap for studying other worlds that may harbor life.
As Earth’s constant companion, the Moon remains crucial to life on our planet, from stabilizing its rotation to influencing tides.
“Despite decades of exploration, many mysteries remain,” Park said. “The Moon continues to be a beacon for scientific discovery.”