"Numerical Simulations of the South Pole-Aitken Impact"
The South Pole-Aitken (SPA) basin, on the far side of the Moon, is the
largest and oldest impact structure still preserved in the solar system.
The crater is about 2500 km in diameter and formed in the Pre-Nectarian
era of lunar history, approximately 4 Gyr ago. At this time, the
thermal state of the Moon was much hotter than it is today. Accretional
energy from the rapidly forming Moon melted the outermost few hundred
kilometers of the Moon. As this magma ocean differentiated and cooled a
60-100-km thick low-density crust formed at the surface; below this the
residual melt, with a higher density, cooled to form the lunar mantle.
The giant SPA impact event punctured the Moon some time during the
cooling of the magma ocean and thus provides a unique window for
studying the lunar interior and the early formative processes of the
Moon. The impact excavated otherwise inaccessible samples of the deep
crust and (possibly) upper mantle, which has inspired proposed sample
return missions. Furthermore, the thermal and rheologic state of the
early Moon played a role in shaping the final structure of the basin. I
will discuss some numerical simulations of the SPA impact event and
their implications regarding site selection for future sample return
missions to the SPA basin, and the thermal state of the Moon at the time
of impact.