Scientists have gained new insight into this dramatic event that created the moon’s largest and oldest known impact crater. This discovery could help future Artemis astronauts explore some of the moon’s deepest secrets.
The findings result from two related studies led in part by researchers at the Center for Lunar Origin and Evolution (CLOE), a team at the Southwest Research Institute within NASA’s Solar System Exploration Research Virtual Laboratory. Taken together, these studies reveal how the giant Antarctic Aitken (SPA) basin formed and where valuable lunar material is now located.
Explore the moon’s largest impact basin
The South Pole-Aitken (SPA) basin is located on the far side of the moon and is one of the oldest preserved structures in the solar system. Because of its enormous size and age, scientists consider it a unique record of the Moon’s early history. Areas near this basin are also being considered for future NASA Artemis missions near the moon’s south pole.
“This basin provides scientists with a unique opportunity to study the Moon’s earliest history,” said Dr. William Bottke, CLOE director and executive director of the SwRI Science Directorate in Boulder, Colorado. He is a co-author of the study. “This impact hit the moon’s surface with such force that material, including part of the moon’s mantle, may have been excavated from deep inside the moon.”
To better understand what happened, researchers used advanced computer simulations to recreate the ancient collision that created the SPA basin. The results show the object approaching from the north and moving south before impacting the moon at a shallow angle.
According to our simulations, this low-angle shock explains the basin’s characteristic elongated and tapered shape.
“Our simulation generates the appropriate shape and properties of the impact basin. It also tells us about the projectile and impact direction that created the impact basin,” said Dr. Shigeru Wakita of Purdue University, lead author of the SPA impact study.
Evidence of differentiated impactors
This modeling shows that the object that caused the collision was not just a chunk of rock. Instead, it may have been a differentiated object with an iron core surrounded by rocky material, similar to a small protoplanet or a differentiated asteroid.
When this object hit the moon, it carved out a deep, uneven cavity, generating intense heat that melted the rocks at the center of the basin. The impact blasted vast amounts of material from both the Moon’s crust and mantle into space. Much of that material eventually fell and accumulated within the basin.
Moon’s mantle material near the Artemis region
In the second study, scientists focused on how this ejected material is distributed beneath and around the basin. Using high-resolution gravity measurements and a model that accounts for material in both the crust and mantle, the researchers found evidence that the SPA basin likely contains significant amounts of rocks derived from the lunar mantle.
This analysis suggests that mantle-derived material is mixed throughout the basin and within the ejecta blanket that surrounds it. Subsequent impacts inside the SPA basin may have dug into these buried deposits and exposed some of them to the surface, potentially making them accessible to robotic missions and future astronauts.
“The exact distribution of mantle material has been a big unknown,” said Dr. Gabriel Gorman of the University of Arizona, lead author of the gravity-based study. “Our model shows that the SPA impact ejected material deep enough to form a significant deposit that should still be accessible today. Most importantly, some of that material may be present at trace levels in the area where the Artemis landing is being considered.”
New target for future lunar exploration
Previous thinking suggested that the deepest material unearthed by the impact may be concentrated in a part of the moon’s basin far from the moon’s south polar region, which is the target of exploration. However, new simulations and gravity analyzes paint a different picture.
Researchers have found that deposits containing mantle material may be widespread in parts of the moon’s south polar region, including areas that future Artemis astronauts may visit and study directly.
“Combining shock and gravity modeling provides a powerful roadmap,” Bottke said. “It tells us not only how SPA formed, but also where to look for rocks that can answer some of our biggest questions about the origin and evolution of the Moon.”
Research shows that “southernly differentiated impactors form the tapered shape of the Moon’s South Pole-Aitken impact basin.” scientific progress. A related paper investigating the gravity of the basin and the structure of ejecta, “Gravity mapping of lunar mantle material from the Antarctic Aitken Basin ejecta,” Geophysical Research Journal: Planets.
