Why Do Two Moon Sides Look So Different? Scientists May Have Found the Answer

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China plans first ever landing on the dark side of the moon - Sputnik International, 1920, 12.04.2022
The face of the Moon that is always visible to Earth is strikingly different from its other side, which we know as the "dark side of the Moon". The latter is significantly more cratered, and this striking dissimilarity has long bothered scientists.
The Apollo-era puzzle of the Moon's two sides looking so different may have been solved, and it seems as though the answer can be explained by referring to the example of the South Pole–Aitken basin (SPA), according to latest research.
The study was led by Brown University, with its press release revealing that the scientists used a computer simulation to examine the impact that actually created the SPA - one of the oldest collisions that ever happened on the Moon. It occurred some 4.3 billion years ago, just at the right time to be responsible for making the changes in the lunar interior that prompted its sides to look different.

“We know that big impacts such as the one that formed the SPA would create a lot of heat,” said Matt Jones of Brown University, who is the study’s lead author. “The question is how that heat affects the Moon’s interior dynamics. What we show is that under any plausible conditions at the time that SPA formed, it ends up concentrating these heat-producing elements on the nearside. We expect that this contributed to the mantle melting that produced the lava flows we see on the surface.”

The researchers from Brown University teamed up with their confreres from Purdue University, the University of Arizona's Lunar and Planetary Laboratory, Stanford University and NASA’s Jet Propulsion Laboratory.
The scientific community first questioned the origin of the lunar sides' differences in Sixties, after the Soviet Luna missions and the US Apollo programme revealed them. Initially, it was only about the differences in volcanic deposits, but future missions revealed that the geochemical composition of the two Moon faces was different as well.
Additionally, the near side of the Moon has 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 such as thorium, which is concentrated largely in volcanic plain Oceanus Procellarum, and is not observed elsewhere on the Moon.
It turns out that this anomaly could also be explained by the emergence of the SPA and how the heat that formed it impacted the PKT. According to the findings, "the KREEP material would have ridden the wave of heat emanating from the SPA impact zone like a surfer", with the heat plume bringing it en masse to the near side of the Moon. The team ran several simulations to explore different scenarios of the impact, but all of them ended up being consistent with KREEP concentrations on the nearside, potentially explaining the PKT anomaly.
“How the PKT formed is arguably the most significant open question in lunar science,” Jones said. “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.”
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