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The Moon always shows the same side to Earth. Scientists call this side the near side. We never see the other side from Earth. They call it the far side.

The two sides look very different. The near side has big, dark plains. These plains came from old volcanoes. The far side has many craters and high land. Its crust, the outer layer, is much thicker.

For many years, scientists did not know why. They had different ideas, but nobody agreed.

In 2024, a Chinese mission called Chang'e-6 went to the far side. It was the first mission to bring back rocks from there. Now scientists could compare rocks from both sides.

A team led by Professor Hejiu Hui studied these rocks. According to ScienceDaily, they found something interesting. Deep inside, the two sides are very similar. But the crust on top is different.

The team has a simple idea. Long ago, Earth was much closer to the Moon. Earth's gravity heated the near side more. Hot magma moved from the near side to the far side. It carried material, and the far side's crust grew thicker.

The study appeared in the journal National Science Review in 2026.

If you look up at the Moon, you always see the same face. This is because the Moon is tidally locked: it always keeps one side facing Earth. As a result, nobody on Earth can see the far side directly.

The two sides are surprisingly different. The near side is covered with wide plains of dark volcanic rock called basalt, and it is rich in elements that scientists call KREEP. The far side, however, is mostly old highland full of craters, and its crust is much thicker. For decades, scientists have argued about why. Some suggested a giant impact, while others pointed to tidal heating or uneven crust growth, but no idea convinced everyone.

In 2024, China's Chang'e-6 mission became the first to bring back samples from the far side. According to ScienceDaily, a team led by Professor Hejiu Hui of Nanjing University compared three types of far-side rock with near-side samples from the Apollo and Chang'e-5 missions.

Their results suggest that the deep mantle is chemically similar on both sides. The crust, however, is not. Far-side samples of a rock called anorthosite contain more magnesium-rich material than similar Apollo rocks, which matches what instruments had already observed from a distance.

The researchers believe the answer lies in uneven heating. After the Moon became tidally locked, Earth was much closer than it is today, so its gravity heated the near side more strongly. Because of this, hot magma flowed towards the far side and carried magnesium-rich material with it. Over time, this material built up a thicker crust. The study was published in the journal National Science Review in 2026.

Gaze up at the Moon on any clear night and you will see exactly the same face that your grandparents saw. The Moon is tidally locked, meaning it rotates in step with its orbit, so one hemisphere permanently faces Earth while the other remains out of view. Yet the hidden hemisphere is not merely out of sight; geologically speaking, it is a different world.

The near side is dominated by vast plains of dark volcanic basalt and is enriched in potassium, rare earth elements and phosphorus, a combination known as KREEP. The far side, by contrast, consists largely of ancient, heavily cratered highlands resting on a considerably thicker crust, with only a scattering of volcanic plains. Explaining this asymmetry has been a long-standing mystery. Over the decades, researchers have proposed a giant impact, tidal heating and lopsided crustal growth, but none of these theories has won universal acceptance.

Part of the problem was a lack of evidence. That changed in 2024, when China's Chang'e-6 became the first mission ever to return samples from the far side, allowing scientists to compare rocks from both hemispheres directly. According to ScienceDaily, a team led by Professor Hejiu Hui of Nanjing University examined three far-side rock types (anorthosites, Mg-suite rocks and mare basalts) alongside near-side material collected by the Apollo and Chang'e-5 missions.

The findings point to a striking contrast between what lies deep below and what sits on the surface. The deep mantle appears chemically alike on both sides, whereas the crust does not: far-side anorthosites hold more magnesium-rich material than their Apollo counterparts, which squares with earlier readings from instruments studying the Moon from a distance.

To account for this, the researchers put forward a model based on uneven heating. Once the Moon had become tidally locked, Earth sat much closer than it does today, and its gravity warmed the near side far more than the far side. This imbalance drove hot magma towards the far side, carrying magnesium-rich material that gradually accumulated into a thicker crust.

The study, published in National Science Review in 2026, may not be the final word on the subject, but it sheds new light on a puzzle that has kept scientists busy for decades.