Astrology

Moon shrinks a few inches per million years as its interior cools, study finds

The moon's radius has shrunk approximately 148 feet during a timespan of 400 million to 800 million years as its interior cools, triggering moonquakes, according to a study in The Planetary Science Journal reported by Discover Magazine. Researchers identified more than 10,000 young faults on the lunar surface using images from the Lunar Reconnaissance Orbiter Camera to reach the estimate.

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How the faults were mapped#

The study was led by planetary geologist Thomas Waters of the Smithsonian National Air and Space Museum, Pravda.Ru reports, and finds the moon's radius decreasing by approximately 0.1 microns per year, a pace that adds up to nearly 148 feet of shrinkage over 400 to 800 million years.

BGNES puts the contraction rate at around 5 to 11 centimetres per million years, translating to roughly 45 metres of lost radius over the same span, and reports that the faults were identified using 17 years of LROC imagery that also revealed wrinkle ridges across the moon's dark basaltic plains.

Pravda.Ru reports that lunar quakes differ from earthquakes because the moon has a single continuous shell rather than separate tectonic plates, so stress from the cooling core builds up within the crust itself instead of migrating to plate boundaries, eventually rupturing the rock once the strain exceeds its strength.

Why the moon's crust cracks at all#

The moon formed around 4.5 billion years ago after the early Earth collided with a protoplanet named Theia, sending molten and vaporized debris into space that later coalesced into the moon, according to NASA as reported by Discover Magazine. Heavy metals like iron sank to form its core while lighter minerals rose to form the mantle and crust.

The moon's interior is still cooling billions of years after its formation, and that cooling causes the whole body to contract, cracking the crust and producing both moonquakes and thrust faults that push rock upward into small cliff-like landforms called lobate scarps, Discover Magazine reports, citing NASA.

Pravda.Ru reports that regions with thicker crust show fewer faults because they resist internal stress better, while areas where the lunar surface is comparatively thin tend to break more easily, a pattern the outlet says the LROC data confirmed is an ongoing process rather than one confined to the ancient past.

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