It was at the end of the and in the decade of that Soviet and American missions revealed two very different faces of the Moon.
The visible face is covered with so-called lunar maria, which appear as large dark spots that reveal ancient lava flows. On the far side, on the other hand, these seas are hardly visible.
The reason for this difference, however, has been a mystery.
A new study by scientists in the United States proposes an explanation to solve the enigma: a gigantic impact billions of years ago.
Two very different faces
“The greatest differences between the visible face and the hidden face of the Moon have to do with the appearance and chemical composition of these lunar regions”, José María Madiedo, an astrophysicist from the Institute of Astrophysics of Andalusia (IAA-CSIC), an expert in asteroid impacts on the Moon, explained to BBC Mundo. Madiedo did not participate in the new study.
“On the visible side there are many large areas covered with solidified lava that are called seas. On the far side, however, these seas are very scarce.“
Madiedo also pointed out that, in terms of composition, the space missions carried out so far they have found great contrasts in the abundance of certain elements.
“Thus, for example, on the visible face have found higher concentrations of potassium, titanium, thorium, phosphorus and other elements of the so-called rare-earth group (REE for its acronym in English – “rare-earth elements“).
“All this reveals that throughout its evolution the Moon must have suffered some type of phenomenon that could give rise to these differences”.
A crater about 2.500 km
The new study, published in the journal Science Advances, indicates that the differences between the faces of the Moon derive from the great impact that the so-called South Pole-Aitken Basin (SPA).
The South Pole-Aitken Basin “is a large crater of impact located in the vicinity of the south pole of the Moon”, explained Madiedo.
“With a diameter of about 2,500 kilometers and a depth of 12 km it is one of the impact structures largest found in objects of the Solar System“.
The location of this basin falls in the area corresponding to the hidden side of the Moon, so it does not it is visible from Earth, added the expert.
“Only the edge of the basin can be seen from our planet, which is made up of a mountain range of about 9 kilometers in altitude.”
Lava flows
The impact that created the basin of the South Pole-Aitken would have caused a huge column of heat that spread through the lunar interior.
As it spread, that column transported a series of rare earths to the side view of the Moon. And the abundance of those heat-generating elements would have contributed to the volcanic activity that created the nearside lava flows.
“We know that large impacts like the one that formed SPA would generate a lot of heat,” he said. in a statement Matt Jones, lead author of the study and a postdoctoral student at Brown University, in the state of Rhode Island, in the United States.
“The question is how this heat affects the interior dynamics of the Moon. What we show is that under any plausible condition at the time SPA was formed, these heat-producing elements end up concentrating on the near side.”
“ This contributed to the melting of the mantle that produced the lava flows that we see on the surface“.
“Like a surfer”
The near side of the Luna hosts a compositional anomaly known as the Procellarum KREEP Terrain (PKT) — a concentration of potassium, rare-earth elements, and phosphorus, along with heat-producing elements like thorium, Brown University explained in their statement.
KREEP appears to be concentrated in and around Oceanus Procellarum, the ma
Scientists performed computer simulations of how heat generated by a giant impact would alter convection patterns in the interior of the Moon and how that might redistribute KREEP material in the lunar mantle.
Models of the lunar interior suggest that it should have been more or less evenly distributed beneath Of the surface. But this new model shows that the uniform distribution would be interrupted by the SPA impact heat column.
“According to the model, the KREEP material would have ridden the heat wave emanating from the impact zone of the SPA like a surfer“, says the statement from Brown University.
As the heat column extended below the Moon’s crust, that material was carried to the near side.
The researchers assure that the work provides a credible explanation of one of the great mysteries about the Moon.
“How formed the PKT is possibly the most important open question in lunar science,” said Jones. “And the South Pole-Aitken impact is one of the most important events in lunar history. This work brings those two things together, and I think our results are really exciting.”
In addition to Brown University, researchers from Purdue University, Stanford University, the Lunar and Planetary Science Laboratory in Arizona, and the Jet Propulsion Laboratory in Arizona participated in the study. The NASA.
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