The mystery of why our Moon has two faces solved


As countries race towards the Moon, new research reveals a previously unknown mystery about why the two sides of the Moon are so different. The solution to this riddle lies in an ancient asteroid collision that rocked the Moon 4.3 billion years ago.

The collision was so significant that it changed the face of Earth’s natural satellite, creating an unequal balance between the side that is visible to us from the planet and the other that remains hidden.

While the nearside (the side the Moon shows Earth) is dominated by the lunar mare – the vast, dark-colored remnants of ancient lava flows, Luna’s farside is filled with craters and virtually devoid of lava flows. large-scale lava.

In a study published in the journal Science Advances, the scientists explained that this strange geographical contrast between the two sides is due to a giant impact billions of years ago near the lunar south pole. The impact was so great that it wreaked havoc on the moon’s mantle.


The new research shows that the impact led to the formation of the moon’s giant South Pole Aitken (SPA) basin, the second-largest impact crater in the solar system. It also created a huge plume of heat that spread across the lunar interior. This plume, according to the researchers, would have transported certain materials – a suite of rare earths and heat-producing elements – to the near side of the Moon.

This concentration of elements would have contributed to volcanism which created volcanic plains on the side that is visible to us. “We know big impacts like the one that formed SPA would create a lot of heat. The question is how does this heat affect the interior dynamics of the Moon,” Matt Jones, Ph.D. candidate at Brown University and lead author of the study said.

The formation of the largest and oldest lunar impact basin, South Pole Aitken (SPA), was a defining event in the evolution of the Moon. (File photo)

Led by a team of researchers from Brown University, Purdue University, Stanford University and NASA’s JPL, the team conducted computer simulations of how the heat generated by the impact giant would alter the convection patterns inside the Moon. They found that the impact led to a unique development inside the mantle that only affected the near side.


The difference between the near and far side of the Moon was first revealed during the US-led Apollo missions and the Soviet Luna missions. The analysis further revealed differences in geochemical composition and that the nearside harbors a compositional anomaly known as the Procellarum KREEP terrane (PKT) – a concentration of potassium (K), rare earth elements ( REE), phosphorus (P), along with heat-producing elements like thorium.

The study reveals that when the object collided with the Moon, it resulted in large lava flows on the nearside filling in ancient impact craters. “What we show is that under all plausible conditions at the time the SPA formed, it eventually concentrated these heat-producing elements on the nearside. We expect this to have contributed to the melting of the mantle that produced the lava flows we see on the surface.” Matt Jones added.

“And the South Pole Aitken impact is one of the most significant events in lunar history. This work brings those two things together, and I think our results are really exciting,” he added.


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