A huge crater on the far side of the Moon has a different shape than we thought: it will be studied in one of the Artemis lunar missions.
About 4.3 billion years ago, a few hundred million years after its formation, the Moon was shattered by a collision with an asteroid which generated its largest and oldest impact crater, as well as one of the largest in the Solar System: the South Pole-Aitken basin, an enormous depression 2500 km in diameter and 12 km deep on the far side of the Moon, near the lunar south pole.
A new detailed analysis of the shape of this crater published on Nature reveals that the impact that left this massive scar on the Moon occurred in the opposite direction than previously thought: from north to south and not vice versa. This is no small detail: the different direction has scientific relevance for our knowledge of the Moon’s past and for the next missions of the Artemis lunar program.
Tapered shape
Accurately mapping the shape of the basin is a complex operation, because the ancient edges of the crater have been smoothed by subsequent impacts. A group of scientists from the University of Arizona used topographic data, lunar gravity data and models of the thickness of the satellite’s crust to come to the conclusion that the South Pole-Aitken Basin has a teardrop shape, which becomes thinner as you go south. The conclusion is that the asteroid that generated it must have hit the Moon coming from the north.
The history of the Moon at your fingertips
This change of direction is important because the Artemis III mission, the first of the Artemis program to include a moon landing, as well as to send a human crew near the lunar south pole, should deposit the astronauts right on the lower edge of the basin, where – based on the new calculated trajectory – the remains of the moon’s interior should have accumulated (the ejectai.e. the debris expelled from the interior of the Moon during the formation of a meteorite crater).
The authors of the study have in fact calculated that the impact would have opened a “window” in the lunar crust, exposing rocky materials rich in residual radioactivity called KREEP (acronym for K, potassium, Rare Earth Elements, rare earths and P, phosphorus) on one side of the basin.
Although the stated purpose of the mission is to search for traces of water ice in the area of the lunar south pole, the possibility of sampling lunar rocks in such a significant point could further increase the scientific value of the mission, because the rocks deposited at the edge of the crater could provide important information about the interior of the Moon and its tumultuous past.
