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AstroAlert: Something big under the Moon’s surface

A false-color topological map of the Moon's South Pole reveals a region where a large metallic asteroid might lie buried below the surface. Image credit: NASA/Goddard Space Flight Center/University of Arizona

Hi everyone,
Astronomers have discovered something big buried beneath the Moon’s surface – probably the relic of an ancient asteroid.
NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission used twin spacecraft to map the gravitational tug at different locations on the Moon. As the two spacecraft orbited, they continuously measured the distance between them. This distance changed slightly whenever they flew over regions of more or less mass – and hence more or less gravity – as their relative speed changed. This allowed scientists to map the local gravitational pull, and hence mass concentration, at different locations. The result is the topological map shown above.

Artist’s drawing of the twin spacecraft that comprised NASA’s GRAIL mission. Image credit: NASA/JPL-Caltech/MIT.

The large blue region, known as the Aitken basin, is the largest impact crater on the Moon, more than a thousand miles across. The circle in the map shows an area within the basin where the local gravitational tug reveals a large object buried nearly 200 miles below the surface. The mass and size of the object indicate it must be very dense, leading scientists to speculate that it could be the remains of an iron-rich asteroid that smashed into this region billions of years ago.

“Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground,” says Peter James of Baylor University. “That’s roughly how much-unexpected mass we detected.”

NASA’s GRAIL mission ended in 2012 when the two spacecraft were intentionally crashed into the lunar surface, however, scientists continue to mine the data they returned. Similar gravity maps provide information about Earth’s lumpy structure. If our planet were perfectly smooth and spherical then the gravitational pull would be the same everywhere. Instead, the local gravity varies from place to place depending on the local mass concentration.

Mountain ranges like the Himalayas have greater concentrations of mass. and hence stronger local gravitational fields.

If you’d like to know more, just click here!
Of course, if you’ve seen the Finnish-German-Australian movies Iron Sky (2012) or Iron Sky 2 (2019), then you’ll know what that object below the Moon’s surface really is….

Best regards,

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