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The far side of the moon, which we can never see from our vantage point on Earth, is strikingly different from the orb we’re used to seeing in the night sky.
The near side we know so well appears darker in places – the result of the vast ancient lava flows, called the moonmare – while the far side is covered in pockmarks and craters but not mare.
Why the two sides of the moon are so different has long puzzled space scientists. However, a study published last week in the journal Science Advances offers a new explanation for this lunar mystery.
Researchers at Brown University have studied the largest impact crater on the Moon, known as the South Pole-Aitken Basin (or SPA). About 1,615 miles (2,600 kilometers) wide and five miles deep, it was formed by a massive space object that slammed into the moon – possibly a wayward dwarf planet – during the formation of the solar system.
The researchers found that the impact that formed the basin would have created a huge plume of heat that spread through the interior of the moon, according to the release. This plume would have transported some material to the near side of the moon, fueling the volcanism that created the volcanic plains.
“We know that big impacts like the one that formed SPA would create a lot of heat,” Matt Jones, a Brown University doctoral student and lead author of the study, said in a news release.
“The question is how does this heat affect the inner dynamics of the Moon. What we show is that under all plausible conditions at the time SPA formed, it eventually concentrates these heat-producing elements on the near side.
“We believe this contributed to the melting of the mantle which produced the lava flows we see on the surface.”
The volcanic plains on the near side of the moon are home to a group of elements such as potassium, rare earth elements, phosphorus among others – known as Procellarum KREEP terrane (PKT) which is rare elsewhere on the moon.
The researchers performed computer simulations of how the heat generated by a giant impact would alter heat transfer patterns inside the Moon, and how that might redistribute KREEP material in the lunar mantle.
According to their model, the KREEP material would have surfed the heat wave emanating from the impact area “like a surfer”, whether the impact was a direct hit or just brushed the moon. As the heat plume spread beneath the lunar crust, this material was eventually funneled to the nearside.
“How PKT formed is arguably the most important open question in lunar science,” Jones said in the press release.
“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.