(CNN) — The far side of the Moon, which we never see from Earth, appears strikingly different from the sphere we are used to seeing in the night sky.
The visible hemisphere we’re so familiar with looks darker in places—the result of large ancient lava flows, called lunar mares—while the far side is covered in pockmarks and craters, but no mare.
Why the two sides of the Moon are so different baffled space scientists for a long time. However, a study published last week in the journal Science Advances comes up with a new explanation for this lunar mystery.
Researchers at Brown University 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, perhaps a rogue dwarf planet, when the solar system was forming.
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 statement. That plume would have carried certain materials to the far side of the Moon, fueling the volcanism that created the volcanic plains.
“We know that large impacts like the one that formed SPA generate a lot of heat,” Matt Jones, a doctoral candidate at Brown University and the study’s lead author, said in an email. Press release.
“The question is how that heat affects the internal dynamics of the Moon. What we show is that under any plausible conditions at the time SPA formed, it ends up concentrating these heat-producing elements on the near side.”
“We hope this may have contributed to the mantle melting that produced the lava flows we see on the surface.”
Volcanic valleys on the near side of the Moon harbor a group of elements including potassium, rare earth elements, phosphorus, among others, known as Procellarum KREEP Terrane (PKT), which is rare elsewhere on the Moon.
The researchers ran computer simulations of how heat generated by a giant impact would alter heat transfer patterns within the Moon, and how that might redistribute KREEP material in the lunar mantle.
According to their model, the KREEP material would have ridden the heat wave emanating from the impact zone “like a surfer,” whether the impact was a direct hit or just grazed the Moon. As the heat plume extended below the Moon’s crust, that material was eventually deposited on the near side.
“How PKT formed is possibly the biggest open question in lunar science,” Jones said in the news release.
“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.”
