This false-color graphic shows the topography of the far side of the Moon. The warmer colors indicate high topography and the bluer colors indicate low topography. (Credit: NASA/Goddard Space Flight Center/University of Arizona) The South Pole-Aitken (SPA) basin is shown by the shades of blue. The dashed circle shows the location of the mass anomaly under the basin.

It is not quite the monolith uncovered at Clavius crater in the epic 2001: A Space Odyssey movie – but still a surprise.

New research points to the existence of a large excess of mass in the Moon’s mantle under the South Pole‐Aitken basin. It may contain metal from an asteroid that crashed into the Moon and formed the crater.

The surprisingly large amount of mass hundreds of miles underneath the South Pole-Aitken basin has been reported in a study – “Deep Structure of the Lunar South Pole-Aitken Basin” — published in the journal Geophysical Research Letters.

Unexpected mass

“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,” said lead author Peter B. James, Ph.D., assistant professor of planetary geophysics in Baylor’s College of Arts & Sciences in a university press statement.

NASA’s twin GRAIL probes.
Credit: NASA

James and his fellow researchers analyzed data from dual spacecraft used for the NASA Gravity Recovery and Interior Laboratory (GRAIL) mission.

“When we combined that with lunar topography data from the Lunar Reconnaissance Orbiter, we discovered the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin,” James said. “One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the Moon’s mantle.”

NASA’s Lunar Reconnaissance Orbiter (LRO).
Credit: NASA/Goddard Science Visualization Studio (SVS)

 

Iron-nickel core

The dense mass — “whatever it is, wherever it came from” — is weighing the basin floor downward by more than half a mile, he said. Computer simulations of large asteroid impacts suggest that, under the right conditions, an iron-nickel core of an asteroid may be dispersed into the upper mantle (the layer between the Moon’s crust and core) during an impact.

Another possibility is that the large mass might be a concentration of dense oxides associated with the last stage of lunar magma ocean solidification.

Important clues

The South Pole‐Aitken (SPA) basin is the largest preserved impact basin on the Moon and perhaps the largest universally recognized impact structure in the solar system.

The formation and structure of the SPA basin hold important clues about the history and evolution of the Moon.

Resource mining

Could this new finding have implications for on-the-spot resource mining?

“For the most part, no – the anomalies that we detect are likely far deeper than any practical drilling could exploit.,” James told Inside Outer Space. “However, modeling by my coauthor Jordan Kendall has suggested that oblique impacts like the one that created SPA may have resulted in some of the impactor core remaining at the surface, mixed in with the crust or ejecta.”

To read the new paper — Deep Structure of the Lunar South Pole-Aitken Basin – go to:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL082252

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