A huge lunar impact, which occurred thousands of years ago, could explain the differences observed on its surface, when comparing the visible side to us and its far side, which we do not see here on Earth. The new study, led by the Chinese Academy of Sciences, relied on simulations to understand the consequences of a large cosmic collision on our natural satellite.
For many decades, astronomers believed that the Moon had a completely patterned surface. However, when the first probes began to study our natural satellite, it was soon revealed that this was not the case.
The differences were not only in appearance, but also in the rocks and materials present on both sides of the Moon. For scientists, in its first thousands of years, the lunar surface was in a primordial state.
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In other words, the entire surface of the Moon would be formed by the same uniform material that resulted from the satellite’s cooling over thousands of years. If these differences exist today, only an event later than this phase would explain them.
Impact on the lunar south pole
Previous studies had already suggested that a massive impact at the lunar south pole that occurred more than 4 billion years ago, forming the Aitken Basin on the far side, would explain these differences on its sides.
Until then, how this impact transformed the surface of the far side into what it is today, is precisely something that is not clear. But in the new study, the researchers simulated this event by considering all the features of the Moon known to date.
The results showed that the impact would have generated heat capable of restarting convection in the early stages of the Moon’s formation. In addition, part of the material from the body that hit it would have penetrated the lunar interior, affecting convection.
Convection is the movement of magma inside a body. As the hotter material rises to the surface and cools, the cooler material sinks and melts—and so on. In its early stages the Moon had this dynamic.
It was also observed that material from the impacting body would have spread across the entire area of the collision, and as convection returned to its normal rate, it was transported to the surface on the far side of the moon. This dynamic would explain the main differences on the Moon’s surface between its two sides.
The study was presented in the journal Nature Geoscience.
