The South Pole-Aitken basin is the largest and oldest visible impact crater on the Moon, a colossal geological feature that has long captivated scientists and astronomers alike. This basin, which stretches over 2,500 kilometers in diameter and reaches depths of up to 13 kilometers, was formed by an immense impact roughly 4 billion years ago. Its age and size make it a significant feature in understanding the Moon’s early history, and it has often been referred to as a lunar time capsule that may hold crucial secrets about the formation of the Moon and the broader solar system.
For years, scientists theorized that the South Pole-Aitken basin was shaped like an oval or ellipse. Based on the distribution of features within the basin, it was believed that the Moon’s surface was struck by an object coming in at a shallow angle, possibly akin to a rock skipping across water. This hypothesis suggested that the debris from the impact would have been dispersed sparingly, especially toward the Moon’s South Pole region, a critical area for NASA’s Artemis missions, which aim to return humans to the lunar surface. If the impact were shallow, it was assumed that the South Pole would have relatively minimal deposits of material from the Moon’s mantle or crust, areas of interest for future exploration.
However, a groundbreaking study led by researchers from the University of Maryland (UMD) has introduced a new perspective on the formation of the South Pole-Aitken basin. This research, published in Earth and Planetary Science Letters, challenges the long-standing hypothesis by proposing that the impact that created the basin was much more direct and vertical. Rather than a shallow grazing blow, the researchers suggest that a more perpendicular strike formed a much rounder, circular crater. The implications of this new theory are far-reaching, not only for the understanding of the Moon’s history but also for future lunar exploration, particularly in the South Pole region, where NASA’s Artemis missions are set to land.
The size and complexity of the South Pole-Aitken basin have made it difficult for scientists to fully understand its structure, despite years of research. As Hannes Bernhardt, the lead author of the study and an assistant research scientist in UMD’s Department of Geology, explains, “It’s challenging to study the South Pole-Aitken basin holistically due to its sheer enormousness, which is why scientists are still trying to learn its shape and size.” The Moon has experienced numerous impacts over the past 4 billion years, which have further obscured the original characteristics of the basin. Yet, despite these challenges, Bernhardt and his team have made significant strides in reconstructing the basin’s formation process.
Using high-resolution data obtained from NASA’s Lunar Reconnaissance Orbiter (LRO), the researchers developed a novel methodology for analyzing the basin’s structure. One of the key findings of their study was the identification and analysis of more than 200 mountain formations scattered across the South Pole-Aitken basin. These mountains, they hypothesize, are ancient remnants of the original impact, remnants that have survived the ravages of time and subsequent impacts. By studying the distribution and shapes of these mountain-like features, the team was able to draw conclusions about the nature of the impact that created the basin.
The team discovered that the mountain formations appeared to be arranged in a pattern that suggested a more circular crater, which indicated a more vertical impact. According to Bernhardt, “A rounder, more circular shape indicates that an object struck the moon’s surface at a more vertical angle, possibly similar to dropping a rock straight down onto the ground.” This circular shape implies that the impact was much more direct than previously thought. It also suggests that the resulting debris from the collision would have been more uniformly distributed across the Moon’s surface, including the South Pole region. This challenges earlier assumptions that debris from the impact would have been scattered unevenly.
The consequences of this new understanding are significant for future lunar exploration. If the South Pole-Aitken basin was formed by a more direct impact, the region surrounding the crater, including the South Pole, could potentially harbor much more material from the Moon’s deeper layers. Specifically, the debris from the lower crust and upper mantle, which is typically inaccessible, could now be within reach. This would provide a unique opportunity to study rocks that may offer insights into the Moon’s chemical composition and formation. For NASA’s Artemis missions, which plan to explore the lunar South Pole, this new theory could guide astronauts and robots to sites where they can collect valuable geological samples.
Bernhardt and his team’s hypothesis has been supported by recent findings from India’s Chandrayaan-3 rover. The rover detected minerals in the South Pole region that appear to be impact debris from the Moon’s mantle, providing further evidence of the more vertical impact. These findings lend credibility to the idea that the South Pole-Aitken basin’s creation involved a direct strike, which in turn scattered mantle material across the surrounding area.
The implications of this research go beyond the immediate findings about the Moon’s formation. According to Bernhardt, this work offers critical information for the planning of future Moon missions. “One of the most exciting implications of our research is how it is applicable to missions to the moon and beyond,” he says. The discovery that materials from the Moon’s lower crust and upper mantle may be more readily accessible could open up new possibilities for lunar exploration. By studying these ancient materials, scientists could gain a deeper understanding of the Moon’s early history and the formative processes that shaped not only the Moon but the entire solar system. The materials that lie beneath the South Pole-Aitken basin may even offer clues about the Moon’s creation, which is thought to have resulted from a massive collision between Earth and another planet-sized object early in the solar system’s history.
The findings also highlight the importance of continued lunar exploration. The South Pole-Aitken basin is not only a geological marvel but also a key to understanding the larger processes that have shaped the Moon and its relationship to Earth. With new technologies and mission strategies, future missions to the Moon may uncover more secrets hidden in the basin and other similar regions. As Bernhardt notes, “Astronauts exploring the lunar South Pole might have easier access to ancient lunar materials that could help us understand how the moon and our solar system came to be.”
Source: University of Maryland