The moon is still geologically active, according to a study

We tend to think of the moon as the archetype of the "dead" world. Not only is there no life, but almost all of its volcanic activity is extinct billions of years ago. Even the youngest lunar lava is old enough to have been marked by numerous craters of impact that have been collected over the centuries, when cosmic debris crashed into the ground.

The clues that the moon is not yet geologically dead exist since the Apollo era, 50 years ago. The Apollo 12, 14, 15 and 16 missions left "earthquake detectors" (seismometers) in working condition on the lunar surface. These transmitted recorded data to the Earth until 1977, showing the vibrations caused by internal "moonquakes". But no one knew if these phenomena were associated with real flaws in motion breaking the surface of the moon or purely internal movements that could also cause tremors. A new study, published in Nature Geoscience, suggests that the moon would actually have active blemishes today.

Another clue to what was still happening on the Moon came in 1972 when Apollo 17 astronauts Gene Cernan and Jack Schmitt inspected a stage in the ground, a few dozen meters high, which they named "the Lee-Lincoln scarf". They and their team of Earth Returning Advisers thought that it could be a geological fault (where a piece of crustal rock has moved away from another), but they were not sure.

A handful of similar examples were noted on photographs taken from Apollo vessels orbiting near the equator of the moon, but it was only in 2010 that the Lunar Reconniassance camera Orbiter Camera, able to record details of less than one meter in diameter, found found scattered around the globe.

It is now widely accepted that they are thrust defects, caused by the cooling of the moon after birth. In this case, the "thermal contraction" causes the contraction of its volume and compresses the surface. This means that the moon is contracting slightly. However, thrust faults do not have to be active and moving, causing other tremors. The same thing happened on Mercury on a much larger scale, where the planetary radius has been reduced by 7 km in the last three years. The largest escarpments are almost a hundred times larger than those on the moon.

Active defects

The analysis shows that these faults are relatively young and do not exceed 50 years or so. But are they active and still moving today? In the new study, Tom Watters of the Smithsonian Institution in the United States and his colleagues used a new method to locate near-surface moonquake locations in Apollo data more accurately than in the past.

The team found that of the 28 shallow earthquakes detected, eight are close to (within 30 km) fault scarves, suggesting that these faults may be active. Six of them occurred when the moon was almost at the greatest distance from the Earth in its orbit. At this point, the contraction stress on the surface is expected to peak and earthquakes should be triggered.

The team also investigated new tracks left by rocks that were dislodged. This is probably due to the jolt on the ground because they are also seen near fault scarves – and have rolled or bounced on a slope. There are also traces of landslide deposits. This, they say, adds to a solid case that fault motions still occur on the moon.

Does this mean that the moon is dangerous for human exploration? The United States has recently announced its intention to go in the next five years, with the goal of creating a lunar base. Fortunately, none of the new discoveries mean that the moon is a hotbed of earthquakes. Moonquakes are rarer and weaker than on Earth, but there are certainly some places close to the faults where it might be best to avoid when planning the bases of the moon.

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This article is republished from The Conversation under a Creative Commons license. Read the original article.