Scientists try to explain the Moon’s strange asymmetry – BGR

• Researchers are looking for an explanation for why the side of the Moon that faces Earth is covered in dark spots, called “maries” or seas.
• These areas can be the result of the radioactive decay of certain elements found in rocks, generating heat and melting the rocks.
• The back of the Moon has almost no dark spots, leading researchers to suggest that the uneven distribution of these elements is to blame.

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The moon is an iconic feature of the night sky. She is always there, simply relaxing us and showing us her face full of personality at all times. It’s cool, but we only see one side, and when astronomers first saw its backside, they were surprised to see that it had very few dark areas compared to the “front” half with smallpox markings.

Now, decades after those observations were first made, researchers are coming up with a theory as to why that might be. The key appears to be the uneven distribution of radioactive elements across the Moon as it formed.

The back of the Moon is much less feature rich than the side we see every night. There are far fewer dark areas, called “mary” or “seas” at the rear, and scientists believed that this was due to an uneven number of impacts from other objects or perhaps to volcanic activity. Now, they believe that a combination of factors is responsible, and some specific isotopes may have played an important role.

Via press release:

Potassium (K), thorium (Th) and uranium (U) are, fundamentally for this story, radioactively unstable elements. This means that they occur in a variety of atomic configurations that have varying numbers of neutrons. These atoms of variable composition are known as ‘isotopes’, some of which are unstable and break apart to produce other elements, producing heat.

Those elements are believed to have been abundant on the near side of the Moon, and the heat of radioactive decay may have enhanced volcanic activity and caused large areas of the near side of the Moon to appear darker.

“Due to the relative lack of erosion processes, the Moon’s surface records geological events from the early history of the Solar System,” Matthieu Laneuville, co-author of the research, said in a statement. “In particular, the regions on the near side of the Moon have concentrations of radioactive elements such as uranium and thorium, unlike anywhere else on the Moon. Understanding the origin of these local uranium and thorium enrichments can help explain the early stages of the Moon’s formation and, as a consequence, conditions on early Earth. “

Simply put, it may have been a random possibility that the side of the Moon we see is covered in dark “seas” while the back is almost completely free of them. In the future, additional research on other moons in our solar system could help provide additional context for this phenomenon.