Published: Tue, May 14, 2019
Science | By

Moonquakes Rattle the Moon as It Shrinks Like a Raisin

The fault scarp or cliff is like a stair-step in the lunar landscape, formed when the near-surface crust is pushed together, breaks, and is thrust upward along a fault as the Moon contracts. When portions of the crust split they move over neighbouring sections of the surface, triggering earthquakes, or rather, moonquakes.

"Some of these quakes can be fairly strong, around five on the Richter Scale".

NASA's Lunar Reconnaissance Orbiter captured this view of the Taurus-Littrow valley, which features a scarp cutting across it. These faults resemble small stair-shaped cliffs, or scarps, when seen from the.

The research paper, "Shallow seismic activity and young thrust faults on the Moon", Thomas Watters, Renee Weber, Geoffrey Collins, Ian Howley, Nicholas Schmerr and Catherine Johnson, was published in the journal Nature Geoscience on May 13, 2019.

Dr Watters led a study into seismometer data collected on the Moon by five Apollo lunar landing missions.

Data from the seismometers placed on the moon during the Apollo 11, 12, 14, 15 and 16 missions revealed 28 moonquakes recorded between 1969 and 1977.

"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", said Watters. The researchers ran 10,000 simulations to calculate the chance of a coincidence producing that many quakes near the faults at the time of greatest stress.

Magnitude 5 moonquakes are causing landslides on the Moon, Nasa researchers say.

"It is truly awesome that the datasets collected by the astronauts so many years ago are still yielding new scientific findings about our moon", Schmerr said.

This prominent thrust fault is one of thousands discovered on the moon by NASA's Lunar Reconnaissance Orbiter (LRO). Over time, the lunar surface darkens due to weathering and radiation, so bright spots are areas where recent activity has exposed areas on the lunar surface.

While other seismic disturbances measured by the Apollo-era seismometers could be attributed to Earth's own gravity making itself felt through space - in the same way that the moon's gravitational pull causes the oceans to rise and fall, so the Earth's pull actually deforms the moon's surface, stretching it into a slightly oblong shape before releasing it back into a sphere - asteroid impacts, or temperature shifts, these "shallow" moonquakes had previously frustrated all attempts to study them.

The moon is not the solar system's only object shrinking with age.

The Trump administration asked Congress on Monday to increase NASA spending next year by an extra $1.6 billion to accommodate the accelerated goal of returning Americans to the surface of the moon by 2024. The moon, which orbits our planet at a distance of about 239,000 miles (385,000 km), has a diameter of about 2,160 miles (3,475 km), a bit more than a quarter of Earth's diameter.

The Apollo missions also detected about one moonquake per day resulting from space rocks hitting the lunar surface.

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