The Moon's South Pole-Aitken basin, the largest and oldest impact basin on the Moon, has long been a subject of scientific fascination. A new study in Science Advances suggests that the basin was formed by an asteroid that arrived from the north, struck at a shallow angle, and flung pieces of deep lunar material across hundreds of kilometers of the far side. This discovery has significant implications for future Artemis astronauts, who may be able to walk across lunar mantle debris and sample ancient interior material without having to drill through the Moon.
The study's simulations narrow the best-fit scenario to a differentiated impactor roughly 260 kilometers wide, traveling at about 13 kilometers per second, and striking the Moon at a shallow angle on a north-to-south trajectory. This differentiated impactor, with a denser core and a rockier outer shell, helps explain the basin's unusual shape. The geometry of the basin also points southward, with the basin tapering towards the south and the crustal transition differing between the northern and southern sides.
The study's findings have significant implications for the Artemis program, which aims to land astronauts near the lunar south pole. The new simulations suggest that some south polar landing areas may sit within reach of South Pole-Aitken ejecta that includes material excavated from deep below the original lunar surface. This means that astronauts collecting ordinary-looking regolith could pick up fragments that were blasted outward billions of years ago from far deeper inside the Moon.
The study also raises the possibility that the impactor that carved the Moon's largest basin may have come from a population of inner solar system bodies whose histories overlapped with the formation zones of the terrestrial planets. Future samples could test pieces of this story, and laboratory analysis may help separate lunar material from traces of impactor contamination. Isotopes, trace elements, and mineral chemistry could then be compared against the model's predictions.
The study's findings have broader implications beyond geology. The South Pole-Aitken impact may be tied to major lunar asymmetries and to the distribution of unusual chemical reservoirs on the Moon. The first crews to work near the south pole may also be working across debris from an impact that reshaped the Moon's early history.
The study's strongest part is that it can be checked. The ejecta is either present in measurable quantities near Artemis landing areas, or it is not. The chemistry either fits a deep lunar source mixed with impactor material, or it points somewhere else. The modeled butterfly-like distribution either helps explain the samples, or future data will force scientists to revise it.
Overall, the study provides a more specific prediction for future missions to test, and it raises the possibility that the Artemis program may be able to sample ancient interior material without having to drill through the Moon. The study also highlights the importance of the South Pole-Aitken basin as a scientifically valuable debris field on the Moon.
