SAN ANTONIO — June 15, 2026 — Scientists from the Center for Lunar Origin and Evolution (CLOE), Southwest Research Institute’s team in NASA’s Solar System Exploration Research Virtual Institute, have helped uncover new details about the formation of the Moon’s oldest and largest impact crater, providing fresh insight into what future Artemis astronauts could encounter near the lunar south pole. The findings are outlined in two new companion studies.
Researchers studied the South Pole-Aitken (SPA) basin, a massive impact structure on the Moon’s far side. Scientists consider the basin one of the Moon’s oldest surviving features, providing insight into the early solar system. Regions near SPA are also potential landing sites for NASA’s Artemis missions.
“The basin offers scientists a rare opportunity to study the Moon’s earliest history,” said Dr. William Bottke, director of CLOE and executive director of SwRI’s Science Directorate in Boulder, Colorado. He is a co-author of the studies. “The collision struck the lunar surface with such force that it may have excavated material from deep inside the Moon, including portions of the lunar mantle.”
Using advanced models and simulations, the research team recreated the SPA-forming impact and identified new evidence about the direction and composition of the object that struck the Moon. Their work shows that an impactor approaching from the north and traveling south hit at a low angle and produced the elongated, tapered shape of the SPA basin.
“Our simulation produces the right shape and nature of the impact basin. It also tells us about the projectile that created it and the direction of the impact,” said Dr. Shigeru Wakita of Purdue University, lead author of the SPA impact study.
The modeling suggests the impactor was not a simple, uniform body but a differentiated object with an iron core surrounded by rock, such as a small protoplanet or differentiated asteroid. As this impactor struck the Moon at a low angle, it excavated a deep, asymmetric cavity and melted the rock in the central basin. The collision lofted large amounts of material from both the lunar crust and mantle, which later settled back onto the basin floor.
In the companion gravity study, researchers analyzed how this ejecta is distributed beneath and around the basin. The team compared high-resolution gravity data with models that include both crustal and mantle material, determining that SPA likely contains substantial amounts of mantle-derived rocks within its interior and mixed into the ejecta blanket surrounding the basin. A few subsequent impacts within the SPA basin appear to have excavated these underlying mantle deposits, bringing some of this material to the surface, where it could be readily sampled by robotic rovers or astronauts during future missions.
“The precise distribution of mantle material has been a big unknown,” said Dr. Gabriel Gowman of the University of Arizona, lead author of the gravity-based study. “Our models indicate that the SPA impact ejected enough deep material to form a significant deposit that should still be accessible today. Most importantly, some of that material at a trace level may exist in regions being considered for the Artemis landings.”
Earlier theories suggested that the deepest ejecta might be confined to parts of the basin far from proposed south polar exploration zones. The new simulations and gravity modeling instead indicate that key deposits of mantle-bearing ejecta may blanket portions of the lunar south polar region, including areas that Artemis astronauts could visit for field studies.
“The combination of impact and gravity modeling gives us a powerful roadmap,” Bottke said. “It tells us not just how SPA formed, but where to look for the rocks that can answer some of our biggest questions about the Moon’s origin and evolution.”
To read the paper titled “A southward differentiated impactor forms the tapered shape of the South Pole-Aitken impact basin on the Moon,” visit the Science Advances website at https://www.science.org/doi/10.1126/sciadv.aea1984 . The companion study on the gravity and ejecta structure of the SPA basin, “Gravity Mapping of Lunar Mantle Material in South Pole-Aitken Basin Ejecta,” can be found in the Journal of Geophysical Research: Planets, accessible at https://doi.org/10.1029/2026JE009665 .
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“A southward differentiated impactor forms the tapered shape of the South Pole-Aitken impact basin on the Moon”
6-May-2026