Quirks & Quarks

Moonquakes show the moon is still geologically 'alive'

A re-analysis of old Apollo-era seismic data combined with recent images taken of the lunar surface suggest that the moon might still be shrinking today and geologically active as a result.

The moon might still be shrinking and so its skin is wrinkling

This prominent thrust fault is one of thousands discovered on the moon by NASA's Lunar Reconnaissance Orbiter (LRO). These faults resemble small stair-shaped cliffs, or scarps, when seen from the lunar surface. The scarps form when one section of the moon's crust (left-pointing arrows) is pushed up over an adjacent section (right-pointing arrows) as the moon's interior cools and shrinks. New research suggests that these faults may still be active today. (LROC NAC frame M190844037LR; NASA/GSFC/Arizona State University/Smithsonian)
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Originally published on May 18, 2019.

A re-analysis of old Apollo-era seismic data combined with recent images taken of the lunar surface suggest that the moon might still be shrinking today and geologically active as a result.

The moon was thought to have cooled and become geologically "dead" many hundreds of millions of years ago. 

But a research team that included Nicholas Schmerr, an assistant professor of geology at the University of Maryland, seems to have found a little life left in our satellite.

A perfect match

Thousands of moonquakes were detected by seismic instruments deployed by Apollo astronauts, which were thought to be from tidal forces, meteor impacts and even the activities of the astronauts themselves.

But Schmerr and his team noticed a correlation between some moonquakes, and geological features mapped by the Lunar Reconnaissance Orbiter (LRO) in 2009.

Image of the Taurus-Littrow Valley, landing site of Apollo 17 showing 1) landslides, 2) boulder run outs, and 3) other features associated with the Lee-Lincoln scarp that is evidence for recent shaking by moonquakes. (NASA/GSFC/Arizona State University/Smithsonian)

The LRO imagery showed many towering scarps as high as a 100 metres, running several kilometres long, all over the moon's surface. They're thought to be caused by the moon's interior cooling down and shrinking.

This leads to the rigid crust of the moon wrinkling around the shrinking core. The tall scarps are the result — as cracks or faults in the crust slide against each other, rising in some places and being pushed down in others. 

Most scientists thought these scarps were created hundreds of millions of years ago. But eight of the Apollo-era moonquake epicentres were located within 19 miles of the scarps, suggesting that they might still be active. The quakes would be from slips along the fault lines, revealing a continuing shrinking and cooling of the interior of the moon.

'We need to go back to the moon'

Scientists like Schmerr are still quite surprised that the moon might still be cooling off.

"For me, these findings emphasize that we need to go back to the moon. There's still a lot of uncertainty about the deep lunar interior and we still don't have a good understanding of the evolution of the lunar crust."

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