Earth’s moon is a constant in the night sky, following predictable phases in its orbit. However, its size likely has been changing over time. A study published January 25 in the Planetary Science Journal found that the moon has shrunk more than 150 feet in circumference as its core gradually cooled over the past few hundred million years.
[Related: The moon is 40 million years older than we thought, according to crystals collected by Apollo astronauts.]
A team of scientists from NASA, the Smithsonian, Arizona State University, and The University of Maryland discovered evidence that the continuing shrinkage led to some surface changes around the Lunar South Pole. The terrain has even changed in areas where NASA hopes to land during the crewed Artemis III mission.
How the moon is like a grape
This lunar shrinking process looks similar to how a grape wrinkles when it becomes a raisin. The moon also wrinkles and creases as it shrinks down. However, a grape has a flexible skin, while the moon has a brittle surface. The brittleness causes faults to form where sections of the crust push up against each other.
The fault formation caused by this continued shrinking often comes with seismic activity like moonquakes. Any locations near these moon fault zones could pose a threat to human exploration there, the same way that those living near fault lines on Earth face a greater risk of earthquakes.
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