“Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground.”
TL;DR
Planetary scientists have uncovered a massive metal anomaly beneath the Moon’s South Pole-Aitken Basin, weighing about 2.18 billion billion kilograms and extending over 300 kilometers deep. This hidden mass, discovered using data from NASA’s GRAIL mission, may be composed of metal from the asteroid that created the crater or dense oxides from the Moon’s early magma ocean. The South Pole-Aitken Basin, the largest preserved crater in the Solar System, offers a unique opportunity to study the Moon’s internal structure and its formation history.
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The Moon holds one of the Solar System’s largest preserved craters, the South Pole-Aitken Basin, situated on the far side of the Moon. This region is the focus of numerous investigations, including India’s first lunar lander mission targeting this area, Artemis 3 planning to land astronauts at the South Pole, and most intriguingly, the discovery of a hidden mass anomaly beneath its surface.
Planetary scientists identified a structure weighing around 2.18 billion billion kilograms, extending over 300 kilometers (186 miles) deep. They believe it may be composed of metal from the asteroid that created the crater.
“Picture burying a mass of metal five times larger than Hawaii’s Big Island underground. That’s roughly the amount of unexpected mass we found,” explained Peter B. James from Baylor University, who led the research.
The team gathered data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission, which tracks subtle variations in the Moon’s gravitational field. These observations offer insight into the Moon’s internal makeup. The detected mass is so significant that it pulls the entire basin floor down by nearly a kilometer (over half a mile). The crater itself spans roughly 2,500 kilometers (1,550 miles) in diameter, creating a considerable gravitational pull.
“When we combined that with lunar topography data from the Lunar Reconnaissance Orbiter, we found an unexpectedly large mass located hundreds of miles beneath the South Pole-Aitken basin,” said James. “One possible explanation is that metal from the asteroid that formed the crater is still embedded in the Moon’s mantle.”
The team ran computer models to explore this anomaly. It’s possible that the asteroid impact, which occurred around 4 billion years ago, left metal embedded in the mantle instead of sinking into the core. Another theory suggests that dense oxides could have formed as the Moon’s magma ocean cooled and solidified.
Various space agencies are drawn to the South Pole-Aitken Basin because of its unique characteristics. It offers a chance to study the Moon’s internal structure and its history and serves as a natural lab to observe the effects of a large impact on a rocky planet’s surface.
However, the South Pole isn’t the only area of the Moon with large, mysterious structures beneath the surface. Astronomers have also detected a significant heat-emitting mass under the Compton and Belkovich craters on the Moon’s far side.
The study was published in Geophysical Research Letters.
