The Mystery of Lunar Granite

Scientists have discovered a large deposit of radioactive granite under the surface of the far side of the Moon.

The formation of granite, which is relatively common on Earth, often depends on the existence of water and plate tectonics that help transform large molten magma below the planet’s surface into masses. It is formed when molten lava underground rises towards the planet’s crust but cools without being scattered by a volcanic eruption. On the Moon, which lacks this process, granite is extremely rare.

The large deposits were discovered by researchers trying to figure out the exact cause of a heat density they observed beneath a region called Compton-Belkovich. Researchers have long suspected that this region on the far side of the Moon, unmatched by the rest of the crust on that side, was formed as a result of volcanic activity. Radioactivity emits heat, and different radioactive substances have different temperatures. When the scientists were able to analyse the temperature of the suspicious matter, they could determine that the only thing that could create this radiation was granite.

Researchers think that this newly discovered granite must have been there since the period when the Moon had active volcanoes, meaning for around 3.5 billion years. The formation also surprised the scientists with its size, with an estimated diameter of 50 kilometres.

The finding will help explain how the early lunar crust was formed. When there is no water in the environment, granite formation takes some extreme situations. The presence of such a granite deposit on the lunar surface without water and plate tectonics raises the question “Did the Moon have more water than we think, during some time, at least at this location? Or was it too hot?”