The moon is the natural satellite of Earth: it has inspired many poets and research workers over centuries.
However, if someone decided to go living there, he would need quake-proof housing. Oh yes!
Surfing the net, I discovered the existence of “moonquakes”: according to a team of 15 planetary scientists, the moon is seismically active. They came to this conclusion through data collected by seismometers (instruments that measure motions of the ground) that Apollo astronauts placed around the moon. The images gathered between 1972 and 1077 revealed that there are different types of moonquakes:
- deep moonquakes (occurring 700 km below the lunar crust) which are probably caused by tides
- vibrations due to the impact of meteorites
- thermal quakes which occur when the cold lunar surface is first illuminated by the sun after two weeks of freeze “lunar night”;
- shallow moonquakes near to the surface
The first three are very mild, while the shallow moonquakes can register up to 5.5 degrees on the Richter scale. A quake of this magnitude on Earth is very energetic and it would cause much damage.
Moreover, shallow moonquakes last more than 10 minutes, while vibrations on Earth die away very quickly because of different chemical weathering: the Earth surface is like a “sponge” that damps down the vibrations, while the moon is dry, cool and inflexible, so during a moonquake it rings for a long time, just like a bell.
Another possible explanation of moonquakes (as the researcher Watters Thomas suggests) is the ongoing scarp formation: we have to take a step back to understand what they are.
In August 2010, NASA examined images collected by the Lunar Reconnaissance Orbiter Camera (LROC) and a team of researchers identified the lobate scarps, some faults typical of the Moon lunar highlands, a sort of lobe-shaped cliff. The scarp formation is recent because the moon formed in an environment of bombardments from meteors and asteroids; so the large craters caused by meteors are older than scarps (indeed they don’t appear on top and the scarps look crisp and undegraded). Scarps are thought to be less than 1 billion years old.
However, new images collected by LRO show linear valleys, known as garben: they’re troughs formed when the lunar surface was stretched and pulled apart. They tell us that forces that shrink the moon were overcome in places by forces that pull it apart; so the contractional forces that shrink the moon aren’t large, otherwise the graben couldn’t form. They’re less than 50 million years old (or probably still less), so this demonstrates that there’s recent geological activity going on. In particular, models of how the moon cooled over time suggest that the Moon was totally molten after its formation and now it should be in a state of contraction because it’s cooling, forcing its surface to shrink. However, if this was true, the graben wouldn’t create because they form when the crust stretches. These findings reveal that moon was not completely molten after it was formed, but only part of it was, forming the magma ocean.
This video will explain you better what’s happening!
Mmm, our satellite is very intriguing…don’t you agree?