A Buried Granite Giant: New Clues to the Moon’s Ancient Past

Scientists have identified a long-hidden anomaly beneath the far side of the Moon, concealed below ancient impact craters and retaining heat billions of years after its formation. The discovery sheds new light on the Moon’s geological past and challenges established ideas about how the lunar interior evolved.

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Moon

What Lies Beneath the Lunar Surface

Beneath the Compton and Belkovich craters on the Moon’s far side, researchers detected a large thermal anomaly. The source appears to be a granite formation roughly 50 kilometers wide, buried deep beneath the surface. Its temperature stands about 10 degrees higher than that of surrounding rocks.

Such a structure remains highly unusual for the Moon, whose surface and crust consist primarily of basaltic lava plains. Scientists identified the formation as a batholith, a massive body of granite that formed as magma cooled slowly within the lunar crust.

On Earth, similar granite intrusions often signal long and complex volcanic histories. Their presence on the Moon, however, came as a surprise.

How Scientists Made the Discovery

Researchers detected the anomaly by analyzing microwave data collected by Chinese lunar orbiters from the Chang’e program. These measurements allow scientists to assess subsurface thermal properties, even when no visible surface features reveal what lies below.

After comparing the data with detailed geological maps of the Moon, scientists concluded that the heat does not come from active magma. Volcanic activity in the region ended around 3.5 billion years ago, long before the Moon entered its geologically quiet phase.

Why Lunar Granite Matters

The elevated temperature likely results from the radioactive decay of elements trapped within the granite. While this process commonly explains heat retention in Earth’s crust, researchers once considered it unlikely on the Moon.

For decades, scientists believed granite formation required water and plate tectonics—conditions absent on the Moon. This discovery shows that complex magmatic processes can occur without them.

The finding broadens understanding of how the Moon evolved and suggests that other rocky bodies in the Solar System may have followed similarly unexpected geological paths.