One of the oldest mysteries about our natural satellite, the Moon, is why its near and far sides are so different. The near side is known for its dark lunar spots, remnants of ancient lava flows, while the far side (popularly called the “far side of the Moon”), almost completely lacks these large-scale features.
Why are both sides so different?
Now, a new study published in the journal Science Advances exposes a new theory, suggesting that the differences may have arisen from a colossal impact billions of years ago.
knowing the moon
The differences between the near and far sides of the Moon were first revealed in the 1960s by the Soviet Luna missions and the US Apollo program. Specifically, the lunar near side hosts a compositional anomaly known as Procellarum KREEP . Terrane (PKT): A concentration of Potassium (K), Rare Earth Elements (REE), Phosphorus (P), along with heat-producing elements such as Thorium. This geological province appears to be concentrated in and around Oceanus Procellarum , the largest of the nearside volcanic plains, but is sparse elsewhere on the Moon. The far side has far fewer volcanic deposits. According to scientists, there could be a connection between the PKT and nearside lava flows.
But why was that set of elements concentrated on the near side?
To answer this question, scientists ran computer simulations of how the heat generated by a large impact would alter convection patterns in the Moon’s interior and how that might redistribute material in the lunar mantle. This new model showed that the KREEP material would have ridden the heat wave emanating from the South Pole-Aitken Basin impact zone like a good surfer, and as the heat plume spread below of the Moon’s crust, material was deposited en masse on the near side.
“We know that large impacts like the one that formed South Pole-Aitken would generate a lot of heat ,” says Matt Jones of Brown University and lead author of the study. “The question is how that heat affects the interior dynamics of the Moon. What we show is that under any plausible conditions at the time the Aitken Basin formed, one of the largest structures in the solar system, it ends up concentrating these heat-producing elements on the near side. We expect this may have contributed to the mantle melting that produced the lava flows we see on the surface .”
Thus, this great impact would have created a column of heat that brought a wide range of chemical elements to the near side of the Moon, but not to the far side, since the upper mantle on the opposite side remained too cold to distribute the same material evenly. Similary.
This hypothesis is quite consistent with the palpable asymmetry between the sides of our natural satellite.
“How PKT formed is possibly the biggest open question in lunar science,” Jones said, “and the South Pole-Aitken impact is one of the biggest events in lunar history. This work brings those two things together, and I think our results are really exciting.”
Referencia: Matt J. Jones, Alexander J. Evans, Brandon C. Johnson, Matthew B. Weller, Jeffrey C. Andrews-Hanna, Sonia M. Tikoo, James T. Keane. A South Pole–Aitken impact origin of the lunar compositional asymmetry. Science Advances, 2022; 8 (14) DOI: 10.1126/sciadv.abm8475
