Did a large impact remix the Moon’s interior? - Ars Technica

As the Moon coalesced from the debris of an impact early in the Solar System's history, the steady stream of orbital impacts is thought to have formed a magma ocean, leaving the body liquid.

A new study links this difference to the Moon's largest impact crater.

The South Pole-Aitken Basin is one of the largest impact craters in the Solar System, but again, we didn't realize it was there until after we put a craft in orbit around the Moon.

Intriguingly, the largest concentration of volcanic mare are found in the north of the near side—roughly on the opposite side of the Moon from the impact itself.

This model combined software that could simulate the impact with models of the Moon's interior that could take into account the heating and additional material of the impact and the gravitational influence of the nearby Earth.

As expected, the model shows that the heat derived from the impact does indeed restart convection within the interior of the Moon.

That's because the body that created the crater also injects a lot of material into the interior of the Moon, and that material gradually spreads out from the site of impact in all directions.

This organized convection is what allows warmer, deep material to make its way to the surface and draws cooler material from the surface to the interior.

The net result is that warm, deep material only makes its way closer to the surface on the side opposite the impact crater.

And the details of the asymmetry are sensitive to the size of the impactor and the viscosity of the material it injects into the lunar interior.