Scientists from the Southwest Research Institute’s Center for Lunar Origin and Evolution (CLOE) have revealed new models of the Moon’s oldest and largest impact crater, the South Pole-Aitken (SPA) basin, providing fresh insights into the event and resulting material deposition on the lunar surface.

The SwRI team behind the new models, which is part of NASA’s Solar System Exploration Research Virtual Institute, said such details will help prepare future Artemis astronauts for what they could encounter during their upcoming missions.

Impact Study Reveals Details About Moon’s Oldest and Largest Crater

In a statement announcing the new models, Dr. William Bottke, director of CLOE and executive director of SwRI’s Science Directorate in Boulder, Colorado, said that the basin is an attractive potential target for future Artemis missions since it offers a “rare opportunity” to study an earlier era in the Moon’s history.

“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,” explained the co-author of the impact study detailing the new research.

Although previous studies have modeled impacts that may have caused the Moon’s oldest and largest crater, the team’s new effort has revealed new evidence about the composition of the impacting object and its likely direction and angle.

“Our simulation produces the right shape and nature of the impact basin,” explained the impact study’s lead author, Dr. Shigeru Wakita of Purdue University. “It also tells us about the projectile that created it and the direction of the impact.”

For example, the new model suggests that the object was not a single, uniform object. Instead, the team found that the impactor was likely a “differentiated” object, such as a protoplanet or asteroid, composed of rock and surrounded by an iron core. The models also found that the object approached from the north “at a low angle” before impacting the Moon’s surface on a southward trajectory.

According to the impact study authors, the impact excavated a deep, “asymmetric” cavity and generated enough energy to melt the rock within the crater’s central basin, resulting in the SPA basin’s elongated, tapered shape. Their models also indicated that the object’s lunar collision “lofted” large amounts of material into the air. Critically, their models also revealed that material from both the lunar crust and mantle was likely ejected before ultimately settling back onto the basin floor.

Exploring Gravity’s Role and the Possibility of ‘Valuable’ Mantle in the Impact Ejecta

To help potential future lunar astronauts, including members of NASA’s Artemis mission, target the most scientifically valuable lunar samples, a second companion study explored the effects of gravity on ejecta distribution beneath and around the impact basin. According to the team behind that effort, their effort involved direct comparisons of high-resolution gravity data with models. Specifically, they wanted to determine if pieces of the Moon’s crust and mantle were included in the ejection.

After comparing the two, the authors of the second study determined that the SPA basin “likely contains substantial amounts of mantle-derived rocks” both within its interior and mixed into the wider ejecta blanket surrounding the basin. Also critical for future missions, the analysis revealed that this material was not all scattered during the initial impact.

Instead, the new models showed that subsequent, smaller impacts appear to have “excavated” these underlying mantle deposits. As a result, the team suggests that there is likely enough material on the surface of the Moon’s oldest and largest crater “where it could be readily sampled by robotic rovers or astronauts during future missions.”

The Studies Provide Future Lunar Missions with a “Powerful Roadmap”

When discussing the significance of the gravity study’s findings, lead author Dr. Gabriel Gowman of the University of Arizona said that before now, the “precise distribution” of lunar mantle material on the Moon’s surface “has been a big unknown.” For example, some previous theories suggested that the deepest ejecta might be found only in parts of the basin that are not currently included in planned Artemis missions.

Now, the team’s new models suggest that the impact that formed the SPA basin “ejected enough deep material to form a significant deposit that should still be accessible today.” More importantly, Dr. Gowman added, some of that scientifically valuable mantle material “at a trace level” may exist in regions currently under consideration for upcoming Artemis landings. Taken together, Bottke said, the two studies can provide a “powerful roadmap” for future lunar scientific missions to the Moon’s oldest and largest crater.

“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,” the researcher explained.

The Impact study “A southward differentiated impactor forms the tapered shape of the South Pole-Aitken impact basin on the Moon” was published in Science Advances.

The gravity study “Gravity Mapping of Lunar Mantle Material in South Pole-Aitken Basin Ejecta” was published in the Journal of Geophysical Research: Planets.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.

In the profound depths of rocky planets like Earth and Mars, the precise chemical states of mantle minerals play a foundational role in shaping planetary evolution. Among these chemical states, the oxidation state of iron profoundly influences mantle melting behaviors, volcanic gas compositions, and ultimately, the nature of a planet’s surface environment. While the elemental presence of iron in the mantle is well-known, the subtle balance between its ferrous (Fe²⁺) and ferric (Fe³⁺) forms remains a challenging frontier to unravel, particularly under the extreme pressures and temperatures encountered in planetary interiors.

The early stages of planetary formation are marked by the existence of a vast magma ocean—a molten silicate layer blanketing the young Earth and Mars. During this epoch, the oxidation state at which iron integrates into forming minerals dictates subsequent mantle properties and evolution. Accurately determining the Fe³⁺ content in minerals crystallized within this magma ocean stands as a critical step toward understanding the oxidation dynamics that influenced core-mantle differentiation and surface volatile release in nascent planets.

A mineral of prime relevance in this context is majorite, a high-pressure silicate phase stable at depths ranging roughly from 500 to 600 kilometers within Earth’s mantle and near the base of the Martian mantle. Its stability under simultaneously high-pressure and high-temperature conditions makes majorite a significant reservoir for iron deep within these planetary interiors. Therefore, quantifying the Fe³⁺ concentration hosted within majorite under early magma ocean conditions bears directly on models of mantle redox evolution and volatile mobility.

Researchers at Ehime University’s Geodynamics Research Center have pioneered the synthesis of Fe³⁺-rich majorite coexisting with molten silicate magma at pressures around 18 gigapascals and temperatures between 2150 and 2200 degrees Celsius. Utilizing a multi-anvil apparatus capable of reproducing these extreme conditions, the team closely simulated the environment of the early magma ocean. High-precision X-ray Absorption Near Edge Structure (XANES) spectroscopy was then employed at the renowned SPring-8 synchrotron facility to accurately assess the valence state of iron within the synthesized majorite crystals.

The findings reveal an unexpectedly high Fe³⁺ content in majorite crystallized from the magma ocean, second only to bridgmanite, Earth’s most abundant lower mantle mineral. This marked enrichment in ferric iron suggests that early mantle minerals could accommodate significant oxidation capacity, challenging earlier assumptions that high-pressure silicates predominantly contain iron in the ferrous state. The implication is that the early mantle harbored more oxidized iron species than previously anticipated, impacting mantle viscosity, melting relations, and the capacity to store volatile elements.

Importantly, as mantle solids ascend toward shallower depths, phase transitions or mineral decompositions can liberate excess Fe³⁺ that no longer fits within the crystal structures. This released ferric iron potentially contributes to the generation of oxidized magmas, influencing volcanic gas emissions and surface oxidation states. Such a mechanism presents a plausible link between deep mantle oxidation states and the chemical makeup of magmas erupted at the surface, offering fresh insights into the geological histories of both Earth and Mars.

The study’s revelations offer a new lens through which to interpret the evolution of mantle oxidation state gradients over geological time. Understanding how iron’s valence shifts across depth-dependent mineralogical boundaries and during mantle convection cycles will refine planetary differentiation models and volatile cycling frameworks. The presence of Fe³⁺-rich majorite highlights a previously underappreciated redox reservoir deep within planetary interiors.

These results not only enhance our appreciation of Earth’s early differentiated mantle but also extend to Mars, where recent seismic and geochemical data point to a similarly complex mantle composition. The redox state plays an outsize role in Martian volcanic outgassing and atmospheric evolution, making this research vital for reconstructing Mars’ geochemical past and assessing its potential habitability.

From a methodological standpoint, the study exemplifies the power of integrating high-pressure experimental petrology with cutting-edge synchrotron techniques. The ability to recreate extreme planetary interior conditions and directly probe valence states in situ offers a transformative approach to addressing longstanding questions about deep Earth and planetary chemistry.

Furthermore, the recognition that Fe³⁺ can be abundant in magma ocean-derived minerals necessitates revisiting thermodynamic and geochemical models of mantle melting and evolution. Oxidation state strongly influences melting temperatures and mantle rheology, thereby controlling convection patterns and surface tectonics. Such feedbacks are essential to comprehend in the broader context of planetary habitability and evolution.

Ultimately, these insights pave the way for multidisciplinary endeavors bridging mineral physics, planetary science, and geochemistry. They underscore the dynamic interplay between deep Earth processes and surface conditions, revealing how the smallest changes in iron’s electron configuration resonate across planetary systems.

This breakthrough in understanding iron’s complex behavior under extreme conditions promises to guide future explorations of terrestrial and extraterrestrial geology. It sets new constraints on the interior states of rocky planets and sharpens our vision of how early planetary environments were sculpted by subtle shifts deep within.

Subject of Research: High-pressure mineralogy and mantle oxidation states in terrestrial and Martian planets.

Article Title: (Not explicitly provided in the original content.)

News Publication Date: (Not indicated in the original content.)

Web References: http://dx.doi.org/10.1029/2025JB033231

References: Journal of Geophysical Research Solid Earth

Image Credits: Hideharu Kuwahara

Keywords:
– Fe³⁺ in mantle minerals
– Majorite synthesis under high pressure
– Magma ocean oxidation states
– Mantle redox evolution
– XANES spectroscopy at SPring-8
– High-pressure experimental petrology
– Earth and Mars mantle comparison
– Ferric iron incorporation in majorite
– Oxidized magma generation
– Planetary interior chemistry
– Lower mantle mineralogy
– Planetary differentiation processes

Day 3 of creation, God formed dry land and initiated life with green plants, establishing essential conditions for future sentient life forms. This day also included the formation of Earth's physical structures. All creations were designed perfectly, paving the way for environmental balance and the development of biodiversity.