The moon may be tectonically active | Hacker News Reader

The moon may be tectonically active

nationalgeographic.com

174 pointsalanwong44 comments

The abstract from the actual study[1]:

> The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults. However, the epicentre locations of these quakes are poorly constrained. Here we present more-accurate estimates of the epicentre locations, based on an algorithm for sparse seismic networks. We found that the epicentres of eight near-surface quakes fall within 30 km of a fault scarp, the distance of the expected strong ground shaking. From an analysis of the timing of these eight events, we found that six occurred when the Moon was less than 15,000 km from the apogee distance. Analytical modelling of tidal forces that contribute to the current lunar stress state indicates that seven near-apogee events within 60 km of a fault scarp occur at or near the time of peak compressional stresses, when fault slip events are most likely. We conclude that the proximity of moonquakes to the young thrust faults together with evidence of regolith disturbance and boulder movements on and near the fault scarps strongly suggest the Moon is tectonically active.

[1] https://www.nature.com/articles/s41561-019-0362-2

Didn't people believe at some point that moon landings themselves caused the Moon to vibrate or something along those lines? Always found that eyebrow-raising.

You might be thinking of impactor probes, in which a vehicle is deliberately crashed into the moon (or another body) in order to generate shockwaves. Previously landed seismic instruments can us this to gather information about the moon's internal structure.

The ascent stages of the Apollo Lunar Modules were deliberately crashed onto the Moon to generate shock waves to support seismology experiments:

https://www.popsci.com/how-apollo-lunar-modules-were-smashed...

Also, for the record this was explicitly discussed in the OP...

There is a "hollow moon" conspiracy theory where one of the pieces of evidence cited is that the moon rang like a bell because of the impact of the lander.

Thanks. It's based on the following data (from the same link):

"Lunar seismicity was recorded by four seismometers placed at the Apollo 12, 14, 15 and 16 landing sites. These seismometers operated from 1969 to 1977 and recorded 28 shallow moonquakes."

and it's a more modern and definitely interesting approach to analyze these measurements. The conclusion which "strongly" suggests that "the Moon is tectonically active" is an argument to measure more in the future. The new measurements and the refinement of their analysis could surely increase our capabilities of modelling the rocks and the layers, even on the Earth. It doesn't however mean that the structure of the Moon fully matches that of Earth.

But also:

https://en.wikipedia.org/wiki/Geology_of_the_Moon

"Studies of the Moon's physical librations (small perturbations to its rotation) furthermore indicate that the core is still molten."

is a Wikipedia claim without the citation. But in NASA's article from 2011:

https://www.nasa.gov/topics/moonmars/features/lunar_core.htm...

"The team's findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles."

Also note the estimated sizes of each layer:

https://www.nasa.gov/images/content/508668main_lunar_core_lg...

Also, the results of the GRAIL mission which ended in 2012 suggest that the lunar crust is thinner than the previous estimates.

> Furthermore, shallow moonquakes lasted a remarkably long time. Once they got going, all continued more than 10 minutes. "The moon was ringing like a bell," Neal says.

(2006) https://www.nasa.gov/exploration/home/15mar_moonquakes.html

Maybe it is ready to hatch. [https://tardis.fandom.com/wiki/Kill_the_Moon_(TV_story)]

My brain had just begun sketching this story. Massive larva emerges, turns out earth was just yolk.

My mind went immediately to Seveneves [0].

[0] https://en.wikipedia.org/wiki/Seveneves

Such an amazing book. The first half at least.

I thought the second half was great except for the part where it ended right in the middle of everything.

That's where the MMORPG is supposed to pick up.

I thought it went too crazy on the tech. The ring habitat was fine but the spinning things that catapult them into space seemed a bit too far fetched.

Sonar Taxlaw is the perfect woman! (Next to my wife, of course.)

As I understand it, the fact that the moon is tectonically active implies that there still is enough heat in the moon's core to cause tectonic activity.

(To anyone who's wondered as well)

The article talks about these movements occurring close to apogee (the point in the Moon's orbit when it's furthest from the earth), so it looks like this activity is driven by gravitational tidal forces rather than internal heat.

The tidal forces are known topic:

https://www.teachastronomy.com/textbook/The-Earth-Moon-Syste...

"Even when there's no water to respond to tidal forces, the solid mass of a planet feels the stress caused by these forces. In fact, tidal forces can heat the interior of a satellite in an elliptical orbit. In that case, the satellite comes closer to the planet during one part of its orbit and there it's subjected to strong stretching forces. As it moves away from the planet the stress is partly released and the body relaxes back toward a more spherical shape. This continual flexing of the satellite creates heat through internal friction, in the same way, that if you flex a tennis ball enough times it becomes warm. This effect is called tidal heating. The more elliptical the orbit, the stronger the tidal heating. Jupiter's large Galilean satellites experience this kind of heating — enough to produce extensive volcanism on Io and possibly create liquid-water oceans beneath the surface of Europa."

The question is how the Moon could be more precisely modeled, and if some refinements to our models used on Earth too could be done, and for all that more measurements would be needed. The paper uses only those made from 1969 to 1977 from the seismometers placed by four Apollo missions, and tries to interpret the data with newer methods than what was done before with the existing measurements, but since 1977 there were no new measurements.

Also:

https://physicsworld.com/a/radioactive-decay-accounts-for-ha...

"About 50% of the heat given off by the Earth is generated by the radioactive decay of elements such as uranium and thorium, and their decay products. That is the conclusion of an international team of physicists that has used the KamLAND detector in Japan to measure the flux of antineutrinos emanating from deep within the Earth."

Does this mean the moon likely has a magnetosphere?

I’m a bit out of my depth here, so someone more knowledgeable correct me if my understanding is wrong.

In the article, they’re stating they believe it’s seismic activity because it’s occurring within some distance of these fault scarps, which also appear to be where the surface displays lines in the images shown in the article?

How are they dismissing it’s not a result of material from space striking the surface? Is it that their sensors are able to disambiguate if the source is from the surface vs deeper in the moon?

> How are they dismissing it’s not a result of material from space striking the surface?

The earthquakes are magnitude 5.5, plugging that into an energy calculator (http://earthalabama.com/energy.html#/) gives a result of 0.2 Hiroshima bombs, which I think would be noticeable.

I wonder if the calculation requires correction due to moon/earth mass difference.

Moment magnitude is generally supposed to be correlated to the amount of energy released, so I would tend to think that it wouldn’t need correction.

>> 0.2 Hiroshima bombs, which I think would be noticeable.

Maybe not. Hiroshima wasn't all that big on geological scales. A medium-sized meteor stroking the moon would have equivalent energy. Tidal forces can also break meteors up, spreading them into streams of smaller bits that land over a period of time. So I am not so dismissive of potential impacts.

Yes, you can estimate the depth below the surface by reading the seismic arrival times. There are compressional waves that travel along the surface, which travel at different speeds than the pressure and compressional waves going straight through the moon.

I think quakes last noticeably longer than impacts, at least if they are large enough. On Earth, there's a fairly well-established empirical correlation[1]. Putting a magnitude of 5.5 into the formula given here suggests a duration of about 70s, if that relationship holds on the Moon.

[1]https://en.wikipedia.org/wiki/Earthquake_duration_magnitude

Looks like Arthur C. Clarke guessed correctly in his sci-fi novel https://en.wikipedia.org/wiki/A_Fall_of_Moondust, where a moonquake causes problems to a "sand-cruiser" full of tourists.

Ha I remember reading that years ago, thanks for the reminder!

In south- and east-asia mythology a frog lives in the moon. This is part of an australian aboriginal myth:

"The frog opened his sleepy eyes, his big body quivered, his face relaxed, and, at last, he burst into a laugh that sounded like rolling thunder. The water poured from his mouth in a flood. It filled the deepest rivers and covered the land. Only the highest mountain peaks were visible, like islands in the sea. Many men and animals were drowned. The pelican-who was a blackfellow at this time -sailed from island to island in a great canoe and rescued any blackfellow he saw" - http://www.sacred-texts.com/aus/mla/mla09.htm

Pun intended.

I rolled my eyes, but then thought "ok, that's fair".

moon worms! joking aside reminds me very much of 50s sci-fi - maybe there will be a mining operation to draw energy from the moon's core in the near future (owned by Jeff Bezos)

Or we set out onto a the goal to tame the moonworms by the year 2119

Moonworms are gentle, misunderstood creatures that have been horribly exploited by mankind.

These majestic beasts are captured when young, and through a process involving electric shock and sub-nuclear bombardment trained to perform tricks for the amusement of lunar tourists who often like to ride on top of their backs and put pictures of their abuse onto Facebook for exploitative likes.

Please donate 100 credits to Save the Moonworm - an offplanet non-profit organized by the head of Jeff Bezos.

“I have ridden the mighty moon worm!” —Al Gore

I wonder if

“Without water, the lunar surface instead gets deformed, stretching from a spherical shape into a more oblong one and back again.”

Is enough energy to keep the core of the moon hot? Like maybe the moons mass alone for for 4+ billion years would have cooled but the additional force of the earth stretching the moon like a rubber band creates heat energy...

Shouldn't that be something like... "lunology"? Doesn't geo- refer to Earth?

*shook

I would have loved if they had named the article "Moon shakes, geologists are shaken".

Still, the notion of shaken geologists because of earthquakes is pretty funny.

Not stirred

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