Honey, I Think The Moon Is Shrinking

No, they’re not making an ill-advised reboot of Honey, I Shrunk The Kids… that we know of. This has to do with our favorite solar system buddy.

In 2010 a team of researchers led by the Smithsonian National Air and Space Museum’s Thomas R. Watters found that the moon is shrinking. The shrinkage, not to be confused with that Seinfeld episode, has taken place over a billion years, as the core of the moon core has cooled and contracted. How the hell do they know this? Science, that’s how. Actually, they’ve been studying the surface of the moon and found 14 cracks and ridges over roughly 10% of the lunar surface. Fast forward to 2015 and the team has found more than 3,200 of these blemishes. The striking thing about this situation is that the moon isn’t shrinking uniformly. If that were the case we’d see the ridges, which form when the moon’s surface cracks and a side of the fracture slips over the other, randomly distributed about the face of the moon.  Watters’ team found that north-south ridges were most prevalent in the equatorial and midlatitude regions and east-west ridges near the poles. In short, the moon is all fucked up. But why?


Okay, it’s not aliens. It’s actually because of the Earth’s tidal forces pulling on the moon. A study published in Geology sheds light on the phenomenon.

Lunar Reconnaissance Orbiter Camera images reveal a vast, globally distributed network of over 3200 lobate thrust fault scarps, making them the most common tectonic landform on the Moon. Based on their small scale and crisp appearance, crosscutting relations with small-diameter impact craters, and rates of infilling of associated small, shallow graben, these fault scarps are estimated to be younger than 50 Ma and may be actively forming today. The non-random distribution of the scarp orientations is inconsistent with isotropic stresses from late-stage global contraction as the sole source of stress. We propose that tidal stresses contribute significantly to the current stress state of the lunar crust. Orbital recession stresses superimposed on stresses from global contraction with the addition of diurnal tidal stresses result in non-isotropic compressional stress and thrust faults consistent with lobate scarp orientations. The addition of diurnal tidal stresses at apogee result in peak stresses that may help trigger coseismic slip events on currently active thrust faults on the Moon.

Right… sooooo is this a big deal? According to Watters it’s really not. In fact, back in 2010 he even said “The kind of radius change and shrinking we’re describing here is so small that you would never notice it,” So it’s like the moon was in the pool… but has junk so large that shrinkage isn’t noticeable.


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