The Moon may be Earth’s closest cosmic neighbor, and the only extraterrestrial body humans have ever trod on, but there are many things we don’t understand. And one of the biggest mysteries is why its two sides are so significantly different.
The researchers have proposed a possible new explanation, backed by experimental evidence. The asymmetry of the Moon, according to a recent document, could be due to an asymmetric distribution of radioactive elements.
The Moon is blocked by tides, which means that one side, the near side, is always facing Earth. When you look at it, you can see that it is covered in dark spots: the lunar maria, wide plains of dark basalt from the ancient volcanic activity within the Moon.
The other side, with its back to Earth, is a different story. The bark is thicker to begin with, with a different composition on the near side. The surface is also much paler, with fewer basalt stains and crater cover.
This is interpreted to mean that basalt flows on the near side covered a large number of craters on the Moon, but why the near side had more volcanic activity than the far side has been a pretty big mystery that lunar scientists have wanted resolve. .
And there is something more peculiar on the near side of the Moon, a geochemically strange region called Procellarum KREEP Terrane.
It is unusually rich in specific elements, which gives it its name: K (the atomic symbol for potassium), REE (rare earth elements) and P (the atomic symbol for phosphorus). It also contains elements such as uranium and thorium, whose radioactive decomposition generates heat.
This KREEP Terrane Procellarum appears to be associated with basalt plains, and its heat-generating properties have previously been shown to have something to do with prominent near-side volcanism.
In fact, thermal modeling of the lunar interior suggests that the radioactive decay of potassium, thorium, and uranium could have provided a near-side heat source for billions of years.
So an international team of scientists set out to find out if this might be the case, conducting experimental analyzes to measure the effect of KREEP on lunar rock.
They mixed a synthetic KREEP composition with moon rock analogs at concentrations of 5, 10, 15, 25, and 50 percent KREEP. These were kept at temperatures ranging from 1,175 to 1,300 degrees Celsius for four to eight days.
The effect was dramatic. The presence of synthetic KREEP in the mixture reduced the analog melting point, producing two to 13 times more melt than in control experiments without KREEP. And this without the contribution of radioactive heat.
To see what happens when this radioactive heat is added to the mix, the team performed numerical modeling. And they discovered that radioactive heating compounds are the effect of KREEP. Together, the two could have contributed to volcanic activity on the near side of the Moon, resulting in the dark regions we see today.
Where did KREEP come from? Well, we still don’t know the exact mechanism, but it is probably a consequence of how the Moon formed. We think that happened about 4.5 billion years ago, when a body the size of Mars called Theia crashed into Earth, sending debris flying into space. That debris recombined on the Moon, but not homogeneously.
Gaining a better understanding of how the Tercel Procellarum KREEP was formed and affected the inner processes on the Moon can help us better understand how it got there.
“Due to the relative lack of erosion processes, the Moon’s surface records geological events from the early history of the Solar System,” explained planetary scientist Matthieu Laneuville of the Earth Life Science Institute in Japan.
“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 Moon formation and, as a consequence, conditions on early Earth. “
The research has been published in Nature Geoscience.