The Moon’s ancient and colossal South Pole-Aitken Basin, a target for NASA’s upcoming Artemis missions, holds critical clues to our celestial neighbor’s violent birth and the solar system’s evolution, with new research offering unprecedented insights into its formation and composition.
As NASA prepares for the ambitious return of American astronauts to the Moon’s surface as part of the Artemis program, a remarkable archive of clues about the Moon’s violent early history and its enduring mysteries lies hidden at its south pole. New research, focusing on the colossal South Pole-Aitken Basin (SPA), is not only shedding light on the Moon’s past but also directly informing where future astronauts might land to collect invaluable samples.
The primary objective for these spacefarers will be to set the stage for a permanent human lunar settlement, but their mission will extend far beyond that. The insights gained from this ancient impact site promise to redefine our understanding of the entire solar system’s formation.
Cratered Faces: The Moon’s Enduring Asymmetry Mystery
For decades, scientists have puzzled over a fundamental asymmetry of the Moon: why its far side is heavily cratered, while the near side, visible from Earth, is relatively smooth. This distinction, clearly visible on the Moon’s surface, hints at a deeper, more complex internal evolution.
The South Pole-Aitken Basin (SPA), an immense crater roughly 1,200 miles from north to south and 1,000 miles from east to west, is central to this mystery. Formed approximately 4.3 billion years ago, it is the Moon’s largest and oldest impact feature, serving as a well-preserved “time capsule” providing evidence of “the process that built and shaped our entire solar system,” as stated by NASA Science.
New Research Redefines SPA’s Origin and Implications
Two recent studies have offered compelling, albeit slightly different, perspectives on the SPA’s formation and what it means for future exploration:
- The Angled Impact Theory: Research led by Jeffrey Andrews-Hanna, a planetary scientist at the University of Arizona, and published on October 8 in Nature, suggests the SPA’s elongated, oval shape comes from a massive asteroid striking the Moon’s far side at an angle, not head-on. Their analysis indicates the asteroid likely arrived from the north, forming a teardrop or avocado shape. This is contrary to earlier assumptions that the impactor came from the south.
- Revealing Deep Lunar Material: Andrews-Hanna’s team found that the down-range (southern) rim of the basin should be buried under thick layers of ejecta—material blasted from deep within the Moon’s interior. This makes it an ideal spot for Artemis missions to study the Moon’s ancient past, especially the distribution of KREEP (Potassium, Rare Earth Elements, and Phosphorus), which are heat-producing radioactive elements. According to a University of Arizona press release, the study showed “the distribution and composition of these materials match the predictions that we get by modeling the latest stages of the evolution of the magma ocean.”
- The Magma Ocean Squeeze: This research directly addresses the Moon’s crustal asymmetry. Scientists believe the early Moon was a global magma ocean. As it cooled, KREEP-rich material, resisting freezing, became concentrated. Andrews-Hanna’s theory proposes that as the crust thickened on the far side, the underlying KREEP-rich magma was “squeezed out” to the near side. The SPA impact created a “window” that confirms this, with radioactive thorium (a KREEP element) abundant on the basin’s western side, but not the eastern.
- The Round Impact Theory: Conversely, new research published in the Earth and Planetary Science Letters journal, led by Hannes Bernhardt of the University of Maryland, suggests the SPA might actually be round, not oval. This theory posits a more vertical impact, akin to dropping a rock straight down, implying a deeper impact and a more even distribution of debris around the crater. This, too, offers significant implications for Artemis, as it means astronauts could more easily access rocks from deep within the Moon’s mantle or crust.
Both studies, despite their differences in impact angle, converge on a critical point: the South Pole-Aitken Basin is a prime location for unlocking the Moon’s fundamental geological history, offering unparalleled access to materials from its deep interior.
Artemis: A New Era of Lunar Exploration
The insights from these studies arrive at a pivotal moment for NASA’s Artemis program, which aims to establish a permanent human presence on the Moon. The south pole region, specifically targeted for crewed landings, is of paramount interest not only for its scientific potential but also for its strategic resources.
Here’s why the south pole is so crucial for Artemis:
- Unveiling Lunar Origins: The SPA, located in the south pole region, offers an unparalleled opportunity to collect samples from the Moon’s deep interior, shedding light on its formation and the broader solar system’s history.
- Access to Deep Crustal Material: Both the angled impact and round impact theories suggest that debris from the impact event will be accessible, allowing astronauts to study materials typically impossible to access from the surface.
- Water Ice Deposits: The south pole is believed to harbor subsurface water ice, a critical resource that could be extracted for drinking water, breathable air, and even rocket fuel for future missions to Mars. This significantly reduces the logistical burden of long-duration human missions.
- Stepping Stone to Mars: Establishing a permanent base at the lunar south pole would serve as a vital testbed and launchpad for future human missions deeper into space, including to Mars.
The Artemis III mission is slated to land astronauts on the lunar surface as early as 2027, marking the first U.S. crewed lunar landing since 1972. Preceding this, the Artemis II mission in 2026 will send four astronauts on a 10-day orbit around the Moon to test the Orion capsule.
The Enduring Value of Lunar Samples
While orbiting spacecraft provide valuable remote sensing data, directly collected lunar samples offer an unparalleled level of detail. These samples will be analyzed by scientists worldwide, revealing granular insights into the Moon’s composition, inner structure, and evolution.
Andrews-Hanna emphasized that such samples will reveal “even more about the early evolution of the moon than had been thought.” The ability to physically examine radioactive elements like thorium in the SPA ejecta will be crucial for validating models of the Moon’s magma ocean solidification and the unique concentration of KREEP-rich material on its near side. These are not merely academic questions; they are fundamental to understanding how rocky bodies form and evolve throughout the universe.
