Giant Ancient Collision May Have ‘Flipped’ the Moon’s Interior, Study Suggests

New analysis of lunar rock suggests that a colossal asteroid strike billions of years ago undamentally altered the Moon's inner structure. Samples from China's Chang'e-6 mission showed an unusually high ratio of heavy potassium isotopes, evidence that extreme heat from a massive impact drove lighter elements into space. This discovery could explain why the Moon's far side, almost devoid of the dark volcanic ‘seas' known as maria, looks so different from the near side.

Chang'e-6 mission uncovers ancient clues

According to Space.com, in June 2024, China's Chang'e-6 probe gathered basaltic rock from the South Pole-Aitken basin, which is one of the largest known impact craters in the solar system. Scientists found that the heavier isotope potassium-41 is enriched compared to potassium-39 in these samples, unlike the Apollo-era rocks from the near side.

The team investigated cosmic rays and volcanic mixing as causes but found that these can have only a minor effect. They therefore concluded that the unusual mix of isotopes was likely to be a remnant of the basin's creation by a colossal impact.

Asteroid impact explains lunar asymmetry

It has also been proposed in the new study that a massive event of this kind would cause several volatile elements (i.e., elements with relatively low boiling points) to vaporise from the Moon. Potassium-39, which has a relatively lower atomic mass, would vaporise from the Moon, leading to a large amount of heavy isotopes being left behind.

In addition, a considerable amount of magma would not develop, allowing there to be less volcanic ‘seas' or ‘maria' on parts of the Moon that are opposite to Earth. Indeed, this likely explains the quite different looks of the two faces of the Moon.