"We found that a number of the quakes recorded in the Apollo data happened very close to the faults seen in the [NASA's Apollo and Lunar Reconnaissance Orbiter missions] LRO imagery".
The scientists discovered that the moon had been shrinking as its interior cooled down and may be getting even smaller as its crust becomes brittle- a bit like what happens to a grape as it dries out to become a raisin.
"It's really remarkable to see how data from almost 50 years ago and from the LRO mission has been combined to advance our understanding of the moon while suggesting where future missions intent on studying the moon's interior processes should go", said Lunar Reconnaissance Orbiter (LRO) Project Scientist John Keller. The innermost planet Mercury boasts numerous thrust faults.
New research from seismometers that were placed on the moon between 1969 and 1977 tells a different story.
From the data analysed and algorithms used, researchers were able to determine eight of the 28 shallow quakes recorded were within 30 kilometres of faults and were visible in lunar images.
"This is exciting as it wasn't clear if the moon had already gone through this period billions of years ago and was tectonically dead, or if it was still active in the present", Schmerr said. Previous research suggested that these deep moonquakes resulted from Earth's gravitational pull on the lunar interior, much as how the moon's gravitational pull on Earth's waters results in the tides, said study co-author Nicholas Schmerr, a planetary seismologist at the University of Maryland at College Park. On Earth, the quakes would have ranged in magnitude from about 2 to 5.
The team also found that six of these moonquakes took place when the moon was at its farthest point from Earth.
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Earth's tectonic activity is driven by its hot interior.
Because the moon doesn't have plate tectonics like Earth, moonquakes are believed to be caused by the cooling of the lunar interior, as well as Earth's gravity. These faults resemble small stair-shaped cliffs, or scarps, when seen from the lunar surface; each is roughly tens of yards high and a few miles long.
The researchers noted other evidence in the orbiter's photos of landslides and boulders at the bottom of bright patches, signaling recent activity. Weathering from solar and space radiation gradually darkens material on the lunar surface, so brighter areas indicate regions that are freshly exposed to space, as expected if a recent moonquake sent material sliding down a cliff. With almost a decade of LRO imagery already available and more on the way in the coming years, the team would like to compare pictures of specific fault regions from different times to look for fresh evidence of recent moonquakes.
"For me, these findings emphasise that we need to go back to the moon". "We learned a lot from the Apollo missions, but they really only scratched the surface. With a larger network of modern seismometers, we could make huge strides in our understanding of the moon's geology", added Schmerr. "It is also a testament to how much can be gained by human spaceflight to the surface of other worlds and underlines the incredible potential for future missions back to the moon and, hopefully someday, Mars".
This release is adapted from text provided by NASA's Goddard Space Flight Center.
NASA's Lunar Reconnaissance Orbiter captured this view of the Taurus-Littrow valley, which features a scarp cutting across it.