The Moon Is Shrinking, Wrinkling, Shaking And Cooling
The moon was thought to be geologically dead, until now.
According to a new study published in the journal Nature Geoscience, the moon has somehow remained tectonically active for billions of years, with moonquakes shaking the satellite much like earthquakes quiver our planet.
The difference is the moon doesn't have tectonic plates.
Over the last several hundred million years the moon's interior has cooled, causing the surface to wrinkle as it shrinks.
Just as a grape wrinkles when it contracts into a raisin, the moon wrinkles as it gets smaller, but the moon's crust is far more brittle and breaks instead of stretching, pushing part of the crust up and over another, forming stair-like cliffs called "thrust faults".
These now litter the moon's surface, averaging a few metres high and several kilometres long.
“The whole idea that a 4.6-billion-year-old rocky body like the moon has managed to stay hot enough in the interior and produce this network of faults just flies in the face of conventional wisdom,” said Thomas Watters, senior scientist in the Center for Earth and Planetary Studies.
While the research is new, the data is not.
In four Apollo missions, beginning with Apollo 12 in 1969, astronauts placed seismometres on the moon which recorded thousands of quakes over eight years ranging from around two to five on the Richter scale.
Scientists have since created a new algorithm to process this data and provide a better understanding of where the moonquakes are coming from.
While most were recorded deep in the interior, 28 were traced to the crust, just 200 kilometres from the surface.
Eight fell within 30 kilometres of young lunar faults -- less than 50 million years old -- that could be seen in images of the moon's surface. Of these, six occurred when the moon was at its farthest point from Earth in its orbit where tidal stress is at its peak, making slip events along the faults more likely.
“We think it’s very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active," Watters said.
Scientists now hope to return to the moon to learn more about what is going on.
It turns out the moon isn't the only world in the solar system to shrink with age.
Mercury has thrust faults of up to 1,000 kilometres long and three kilometres high, suggesting it has shrunk much more than the moon.