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The Moon Has a Fluid Outer Core
mapkinase writes with this excerpt from Discovery News:
"The Apollo Passive Seismic Experiment recorded motions of the ground from moonquakes and other activities generating sound waves until late 1977. The network was too limited to directly monitor waves bouncing off or scattered by the moon's core, leaving scientists dependent on more indirect techniques, such as measuring minute gravitational changes, to craft a picture of the moon's interior. Those models turned out to be pretty accurate, says lead scientist Renee Weber, with NASA's Marshall Space Flight Center in Huntsville, Ala. The new research confirms the existence of a solid inner core and liquid outer layer, similar to Earth's. Unlike Earth, the moon also has a partly melted, mushy layer over that."
Molten cheese?
IIRC, there's still some debate as to how much of the interior heat of the Earth is due to radioactive decay and how much is residual heat leftover from the planet's formation. Remember that the Earth/Moon system originated as two bodies of similar mass that collided a few billion years back; both would have been fully molten, surface to core, when the proverbial dust had settled. Millennia would pass before either had a solid surface.
It might be that the internal heat of the Earth is partly residual, with radioactive decay delaying cooling by adding more heat. Regardless of the proportion of residual to radioactive heat, the moon should be less molten than the Earth, if only due to the square-cube law dictating the Earth will cool more slowly. So the science in TFA is actually pretty interesting.
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Looks a lot like other moons, and even like Mercury, and not totally unlike Mars.
Its the only moon in a warn (not hot, not frozen) zone, and its far from uniform.
If it was totally solid you might expect more landscape features created by impact. But because it is simi-fluid and reasonably large, gravitational forces keep super-large scale features from being formed.
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I know I'm not suposed to engage crazy people. But most things in the solar system look unique, its not that big a place, and there are other grey lumps of rock and dirt here.
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I suppose its part of the picture. I read somewhere that the core is offset towards the Earth by about 1 km. The moon does wobble slightly. Telescopes on Earth can see about 60% of the lunar surface by observing at the right times. The sun will be continually pulling at the moon to point towards it.
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I also read that the daytime heat on the moon is gone one metre below the surface.
Keep in mind that daytime heat has only two weeks to penetrate before it is replaced with some serious nighttime cooling. You wouldn't have to go far down before the heating and cooling tend to cancel each other out.
incorrect. mercury and mars, have varying atmospheric or environmental conditions shaping them. there is a reason why they are that flat, and uniform. there is something grinding the stones to sand.
you have easily accepted the fluidity that was just a new proposition. it is equally interesting that you havent asked why the moon was already that fine grained up till this point. it is as if it was custom ordered to perfectly absorb meteorites, being not too soft, or not too hard, and finely grained. there is no other occasion like that in solar system.
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Incorrect. Elements segregate in the Earth (and Moon) based on chemical affinities, not on weight. And this is just relative abundance (relative to composition of the solar system). You get all elements in all parts of the Earth, but there is relatively more lithophile elements in the crust, and relatively more siderophile elements in the core.
And uranium is a lithophile, so it is more concentrated in the crust. It still keeps the core warm though. The crust is like an electric blanket, it insulates and provides heat (through radioactivity) to the core (and mantle).
incorrect. mercury and mars, have varying atmospheric or environmental conditions shaping them. there is a reason why they are that flat, and uniform.
Mars is flat?? I don't know where you get that idea from. Mars has mountains and valleys that dwarf anything we have on earth. Olympus Mons is over 21km tall, almost 3 times the height of anything on earth.
Forgiven.
1. Some theories said the moon had to be solid. It's smaller than Earth so it ought to have cooled faster. It has a lower average density than Earth so it shouldn't have lots of radioactive elements in its core, adding heat as they decay (Since all the long lasting radioactive isotopes are dense metals).
2. You were probably informed that its calculated density showed the Moon couldn't have enough pressure near its center for an inner core to be crystaline iron, with an outer core of molten iron. That's what we think Earth is like. It explains our strong magnetic field, and its lack would explain why the Moon (and Mars, Mercury and Venus, also all somewhat smaller than Earth) doesn't (don't) have a similar magnetic field (s). That's only partly changed. This evidence suggests the moon has an inner core and outer core that are respectively solid and liquid (like Earth). It has a boundary layer above the outer core that goes gradually from liquid to slushy to sort of solid (unlike Earth, where the next boundary is pretty sharply defined). It has a solid crust (like Earth). So what's different besides that interesting slushyness? Iron. Earth's core is probably nearly all Iron, packed into a very regular crystal. Huge chunks of core have been pressurised enough to erase the irregularities between smaller crystals and merge them into one crystal structure wherever possible until you get to the top bit where it becomes more a bunch of discreet crystals and then molten Iron in the outer core. The Moon's core appears to be solid surrounded by liquid, but it doesn't appear to be almost all Iron - it still has much lighter material mixed in compared to Earth's core. So, if your high school geology teacher said the Moon couldn't have a solid Iron inner core with the vastest part of it in a regular crystal state, and a molten outer core, they may still have gotten it right, but if they went farther and said it couldn't be solid surrounded by liquid or couldn't be liquid at all, they definitely went too far in explaining the limited observations of the time.
3. Some of the Selenologic data comes from Apollo. Some comes from more recent efforts like the south polar impactor mission. Not all that data matches, so it's probable this all needs more work and new instrumentation to be more confident we eventually get the whole model right. What's happened here is we have gotten closer to making the kind and quality of observations we have made to Earth itself during many earthquakes and other events, but arguably we are still not 100% caught up.
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> the degree of molten-ness depends mostly on composition, not square-cubiness.
The rate of heat production is proportional to volume while the rate of heat loss is proportional to surface area so equilibrium temperature is proportional to the 3/2 power of diameter.
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Check out the temperature at 2 metres depth. I reckon your temperate zone is close enough to the surface that the regolith at that depth will be as dry as it is at the surface (except in cold polar craters).
Conclusion: other than at the pole the moon may be too hot and dry for life as we know it.
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