Earth's moon is shrinking and quaking, study says
- par Amanda Heroux
- dans Science
- — Déc 1, 2019
NASA officials presented an updated budget request to the US Congress this Monday.
While the seismometer data has been held for decades, combining it with the LRO Mission mapping is new.
Astronauts placed five seismometers on the moon's surface during the Apollo 11, 12, 14, 15 and 16 missions. While these seismometers have long since gone silent, they returned up to eight years of data while active. In the process, they recorded 28 shallow moonquakes.
Of the 28 moonquakes measured, the team found at least eight were caused by true tectonic activity, with an equivalent natural disaster magnitude of about 2 to 5.
A new paper in Nature Geoscience discusses these findings, which could collectively demonstrate that the Moon is not, in fact, a geologically dead world. The orbiter was able to snap a shot of the impact zone, and by digging through the LROC photo archive from 2016, researchers were able to put together and post a before and after image of the location.
Eight moonquakes were discovered to have epicenters within 19 miles (31 km) of geological formations called thrust faults. Analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near-apogee events within 60km of a fault scarp occur at or near the time of peak compressional stresses, when fault slip events are most likely. And as it shrinks, the moon actively produces moonquakes along the faults.
The timing of the moonquakes was also important: numerous quakes occurred when the Moon was at or near its apogee - the furthest point in its orbit from Earth - when the tidal stresses on the rocky orb are at their highest.
"We have to figure out how small rocky bodies like the Moon can retain their interior heat over billions of years". Two are associated with vibrations originating underground - deep and shallow ones - another is due to vibrations from the impact of meteorites and the last variety are thermal quakes; these are formed after the Moon has undergone two weeks of freezing nights and is then subsequently warmed by the morning Sun, causing the surface layers to expand.
Beresheet's impact site appears as a "white impact halo" in the new image from the Lunar Reconnaissance Orbiter (LRO), NASA officials said in a statement.
Of the eight moonquakes that occurred close to visible thrust faults in the LRO data, six took place when the Moon was at its most distant orbital point relative to the Earth.
As a result, the moon has become about 150 feet (50 meters) "skinnier" over the past several hundred million years. This shrinkage creates "wrinkles" on the Moon's skin, except the rock isn't flexible. Eventually, it breaks, forming thrust faults. This shrinking is causing wrinkles in the crust of the moon, and it is, in turn, resulting in the rise of seismic activities. But the lunar faults, like Earth fault lines, are similar in that they're where pieces of the surface sometimes rub against each other, causing quakes that can reverberate throughout the planet.
Rumblings under the lunar surface captured by Apollo-era equipment may be a sign that the Moon is still tectonically active, researchers say.
