In a groundbreaking study, researchers have uncovered a mysterious large mass of material hidden beneath the South Pole-Aitken basin, the largest preserved impact crater in our solar system. Located on the far side of the Moon, this basin stretches approximately 2,000 kilometers in diameter and reaches depths of several miles. Despite its immense size, the crater cannot be seen from Earth due to its location on the lunar far side.
Gravity and Topography Data Reveal Subsurface Mass
By analyzing data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission and the Lunar Reconnaissance Orbiter (LRO), scientists were able to measure subtle changes in the strength of gravity around the Moon. When combined with lunar topography data, the researchers discovered an unexpectedly large amount of mass lurking hundreds of miles beneath the surface of the South Pole-Aitken basin.
The excess mass, estimated to be at least 2.18 × 10^18 kg, likely extends to depths of more than 300 kilometers. This anomaly is so substantial that it weighs the basin floor downward by more than half a mile. Lead author Peter B. James, assistant professor of planetary geophysics at Baylor University, puts the mass anomaly into perspective: “Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground. That’s roughly how much unexpected mass we detected.”
Possible Origins of the Anomalous Mass
The origin of this anomalous mass beneath the South Pole-Aitken basin remains a mystery, but scientists have proposed two plausible explanations. The leading hypothesis suggests that the mass could be metal from the core of a differentiated asteroid that crashed into the Moon and formed the crater billions of years ago.
Computer simulations of large asteroid impacts indicate that under the right conditions, the iron-nickel core of an asteroid could be dispersed into the Moon’s upper mantle during such a collision. James and his colleagues calculated that a sufficiently dispersed core of the asteroid that created the impact could remain suspended in the mantle rather than sinking to the lunar core.
An alternative explanation proposes that the mass anomaly could be a concentration of dense oxides associated with the final stages of the lunar magma ocean solidification. As the Moon cooled and solidified after its formation, these dense oxides may have accumulated beneath the basin.
Implications for Lunar History and Evolution
The discovery of this massive anomaly beneath the South Pole-Aitken basin has significant implications for our understanding of the Moon’s formation and evolution. The basin is thought to have formed approximately 4 billion years ago, during a period of intense bombardment in the early solar system.
James emphasizes the importance of this finding, stating that the South Pole-Aitken basin is “one of the best natural laboratories for studying catastrophic impact events, an ancient process that shaped all of the rocky planets and moons we see today.”
The presence of the mass anomaly also sheds light on the rigidity of the lunar interior. If the mass was indeed deposited during the basin-forming impact event billions of years ago, its persistence to the present day suggests that the Moon’s lower mantle has a high viscosity and a relatively cool temperature, which prevented the anomaly from sinking to the core.
Future Exploration and Research
The findings of this study underscore the need for further exploration and research of the South Pole-Aitken basin and the lunar interior. NASA’s Artemis program aims to return humans to the Moon and establish a sustainable presence on the lunar surface, with the South Pole as a potential landing site.
In-situ exploration and sample return missions targeting the basin could provide valuable insights into the composition and origin of the anomalous mass, as well as the formation and evolution of the Moon itself. Additionally, continued analysis of data from lunar orbiters and future missions will help refine our understanding of the subsurface structure and dynamics of Earth’s celestial companion.
The discovery of this massive anomaly beneath the Moon’s largest impact crater is a testament to the power of combining multiple datasets and the importance of studying the lunar interior. As we continue to explore and unravel the mysteries of our nearest neighbor, findings like these will undoubtedly shape our understanding of the Moon’s complex history and the processes that have sculpted the solar system we inhabit.
