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The Moon may look like a piece of cold, dead rock floating in space, but there could still be life in the old one. Geologists have found indications of tectonic activity on the near side of the Moon that they believe is recent, and may even be ongoing today.
The presence of relatively cool rocks and rocks reveals a system of ridges on the Moon’s face that suggests recent tectonic motion.
“There is an assumption that the Moon is long dead, but we continue to discover that this is not the case,” said planetary geologist Peter Schultz of Brown University. “Based on this document, it appears that the Moon may still be cracking and cracking, potentially today, and we can see the evidence on these ridges.”
We have known since the Apollo era that the Moon is still rumbling. Seismometers placed on the lunar surface by Apollo astronauts decades ago unexpectedly revealed faint moon tremors far below the surface and shallower tectonic tremors in the crust.
Geologists concluded that deep moon earthquakes were the result of gravitational interactions with Earth, which places a lot of stress on the Moon.
The shallow moon tremors were a little harder to pin down. They resembled earthquakes in force, but the Moon doesn’t have tectonic plates like the ones that make Earth shudder, so the tremors defied easy explanation. Last year, however, scientists found a possibility: Tectonic tremors, they said, are caused by the shrinking of the Moon as it continues to cool 4.5 billion years after its formation.
Other new ridges have also been detected around the lava-filled impact basins; however, that can be attributed to the flaccidity associated with the weight of the lava. But this latest discovery doesn’t fit with that.
“The distribution we found here asks for a different explanation,” said Schultz.
He and planetary geologist Adomas Valantinas from the University of Bern in Germany studied data taken from the Diviner instrument aboard NASA’s Lunar Reconnaissance Orbiter, an instrument that measures the temperature of the lunar surface.
Because exposed rock bed and thick surfaces retain heat more effectively than regolith-covered surfaces (dirt, dust, and debris), this can be used to detect those surfaces during the lunar night.
“The exposed blocks on the surface have a relatively short shelf life because regolith accumulation occurs constantly,” Schultz explained. “So when we see them, there must be some explanation of how and why they were exposed in certain places.”
(Valantinas and Schultz, Geology, 2020)
The team then analyzed the data collected by the orbiting spacecraft when the near side of the Moon was enveloped in the 14 days of dark lunar night, and identified more than 500 patches of exposed parent rock that appeared to form a pattern to through the lunar maria.
When the team traced these patches, they found that they almost exactly matched deep, ancient cracks discovered in 2014.
“It’s almost a one-to-one correlation,” said Schultz. “That makes us think that what we are seeing is a continuous process driven by things that happen inside the Moon.”
Once upon a time, these crevices had been fed with magma from the depths of the lunar interior. And its distribution, found by the 2014 article, was consistent with thermal stresses, differential cooling, and magmatic activity.
But more recent work found that the distribution of faults on the near lunar side is inconsistent with what we would expect from global cooling. And the stress of Earth’s tides would be too weak to cause the observed geology, the researchers wrote in their article.
The new findings suggest that the ridges are still rising upward. But the combination of the ridges with the magma-filled cracks presents one possible explanation: the South Pole-Aitken basin.
This is a colossal impact crater on the other side of the Moon. At 2,500 kilometers (1,550 miles) in diameter, it covers a quarter of the lunar surface and is one of the largest known impact craters in the Solar System. It is possible, the team proposes, that this impact shook the Moon at its core.
This could have produced a crack system on the near side, which then filled with magma. The rising ridges are, then, in this model, the continuing response to that partially devastating Moon event long ago.
“Giant impacts have lasting effects,” said Schultz. “The Moon has a long memory. What we are seeing today on the surface is testimony to its long memory and secrets that it still holds.”
The research has been published in geology.
