The moon has long puzzled scientists with its “two faces.”
The near side, which always faces Earth, looks very different from the mysterious far side that we never see.
Now, a new study suggests that the interior of the far side may actually be colder than the near side, helping to explain why the two halves of the moon evolved so differently.
The research, published in Nature Geoscience, analyzed rock and soil fragments collected by China’s Chang’e 6 spacecraft, which last year became the first mission to bring back samples from the far side of the moon.
By studying these materials, scientists discovered that the rocks formed at temperatures about 100 degrees Celsius cooler than similar samples from the near side.
The team dated the sample at about 2.8 billion years old and measured its chemical composition to estimate how hot it was when it formed deep inside the moon.
The rock appeared to have crystallized from lava at around 1,100 degrees Celsius, compared to about 1,200 degrees Celsius for near-side rocks gathered by the Apollo missions.
Professor Yang Li of UCL and Peking University, a co-author of the study, explained: “The near side and far side of the moon are very different at the surface and potentially in the interior. We call it the two-faced moon.
A dramatic difference in temperature between the two sides has long been hypothesized, but our study provides the first evidence using real samples.”
The far side of the moon is thicker, more mountainous, and more heavily cratered, while the near side shows more volcanic activity, with large dark patches of cooled lava.
Scientists believe these differences could be linked to how heat-producing elements like uranium, thorium, and potassium are distributed inside the moon.
These elements generate heat as they decay, and they appear to be concentrated on the near side.
How they ended up unevenly distributed is still debated. One idea is that a giant asteroid or planetary body smashed into the far side early in the moon’s history, shifting these elements toward the near side.
Another theory suggests the moon may once have collided with a smaller “companion moon,” leaving behind two geologically distinct halves. It is also possible that Earth’s gravity has kept the near side hotter.
For this study, scientists analyzed about 300 grams of lunar soil using advanced probes that measure mineral composition and isotopes. Their results consistently showed that the far side’s interior was cooler by about 70 to 100 degrees Celsius.
While the exact temperatures of the moon’s mantle today remain unknown, any imbalance would likely persist for billions of years, since the moon cools very slowly after its fiery beginnings as molten rock.
These findings bring us closer to understanding the deep mystery of why the moon has two very different faces. But as researchers continue to study the samples, the story of the moon’s hidden far side is still unfolding.
