Jun 13, 2019 I Brett Tingley

Massive Metallic Anomaly Discovered On the Far Side of the Moon

Something strange has just been detected below the surface of the Moon. Scientists at Baylor University have analyzed data gathered from NASA’s 2011-2012 GRAIL mission and have found that a huge, dense mass of metal lies just under the surface of the Moon's South Pole-Aitken basin, one of the largest known craters in our solar system. While it’s still somewhat unknown where the metallic mass could have come from, the researchers believe it’s likely the remnants of a huge metal asteroid which impacted with the moon and formed the crater itself.

The South Pole-Aitken basin lies on the far side of the moon and measures over 2,500 km (1,600 miles) at its widest point - over half the width of the United States - and is some 13 km (8 miles) deep. The mass of the metallic deposit in the basin has weighed down the surface of the crater by more than half a mile and appears to be several miles deep.

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Topographic map of the South Pole–Aitken basin, with darker colors representing low elevation.

"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," lead author Peter B. James said in a press release. James and colleagues have published a study of the Moon’s metal mass in which they argue that “plausible sources for this anomaly include metal from the core of a differentiated impactor or oxides from the last stage of magma ocean crystallization.”

While the oxidation of magma remains a possibility, most of the data gathered about the mass supports the theory that an iron-and-nickel-rich asteroid struck the far side of the moon about 4 billions of years ago, creating the crater and leaving its metals embedded in the Moon’s mantle. Thus, the basin and this metallic mass offer the perfect opportunity to study the effects of ancient catastrophic impacts.

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The South Pole–Aitken basin is the darker area at the bottom of the image.

Last month, an international team of scientists also using GRAIL published a study claiming that the Moon’s curious asymmetries could have been caused by a collision with a dwarf planet. The crust of the far side of the Moon is much thicker than on the 'near' side, the composition of the two sides are vastly different, and scientists still aren't sure why. Could this metallic mass be the long-dead core of a dwarf planet? 

Brett Tingley

Brett Tingley is a writer and musician living in the ancient Appalachian mountains.

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