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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?
I thought the solid Moon was a done deal. Was I misinformed, or is this groundbreaking science (forgive the pun)?
I was hoping for caramel.
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So if the moon started out with heavy elements like uranium, a lot of them will be in the core now, keeping it warm. The crust is mainly light stuff, silicon, etc, with the occasional lump of meteoric iron.
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it looks artificial like no other thing in the solar system does. so much that that many asteroids hitting over all those aeons only had had created that many impact and changed its landscape only so much. absurdly, its uniform gray dust.
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I suppose a bit of heat comes from being swung around in the sun's gravitational field, but the crust would feel that more than the core. I don't see why there can't be a lot of radioactive material in the core. Additionally the Apollo heat flow experiment should have shown how much heat is actually being lost through the crust. Maybe the core hasn't had enough time to cool entirely. Its a pretty small core.
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Arthur C. Clarke had a novel where they used the molten moon core as a weapon against spaceships.
What about the Earth's gravitational field? Wouldn't that have a significant effect as well?
Sig Battery depleted. Reverting to safe mode.
> Maybe the core hasn't had enough time to cool entirely. Its a pretty small core.
A smaller planet cools faster.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
My understanding is that it still has radioactives. Also there's modest tidal forces acting on the Moon (mostly from the Sun). I guess the last heat source would be heat of crystallization of the liquid core. I'm a bit surprised that the core is still liquid. It must be that the Moon is a great thermal insulator right now.
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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Well yeah. Its because the moon is in orbit around the sun and the moon at the same time. The orbit has to be fairly eccentric around both so the changing intensity of both fields raises small tides in the lunar crust.
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> Maybe the core hasn't had enough time to cool entirely. Its a pretty small core.
A smaller planet cools faster.
Yes.
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What about the Earth's gravitational field? Wouldn't that have a significant effect as well?
I think the point was that it's going around the sun so it has sunlight shining on it. IANAA but I don't believe the Moon is subject to any significant 'kneading' like Titan; I imagine this is because the Moon is so large compared to the planet it's orbiting.
If God forks the Universe every time you roll a die, he'd better have a damned good memory.
It must be that the Moon is a great thermal insulator right now.
Reminds me that Astronauts working on the surface had to keep their suits as clean as possible to help stay cool. Partly because being dark means you collect more heat from the sun but also because the dust is a good insulator. If the crust is made of the same stuff there won't be a lot of heat flowing through it. I also read that the daytime heat on the moon is gone one metre below the surface.
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Would the fact that the moon always has the same face towards earth (tidally locked?) accentuate or mitigate any effects of Earths gravity in heat generation withing the moon?
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Is that what you are saying?
Mit der Dummheit kämpfen Götter selbst vergebens
What's that, the semiautolunacentric model?
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
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.
What's that, the semiautolunacentric model?
Consider Janus and Epimetheus. Do they orbit each other, or do they orbit Saturn? Both statements are true. This is also the case for the Moon and the Earth. Its really a difference of degree.
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There have been discussions of a probe to Uranus. Don't the Slashdot editors realize how many more silly jokes and pageviews this could generate? As a stockholder in GKNT, I demand that you post a story about the Uranus probe.
Once the outer surface has solidified, it insulates the core quite well. The moon's surface temperature drops to 100K (almost cold enough to liquify oxygen in Earth's atmosphere) in the night, which is pretty cold considering that the sun heats it to 390K (hotter than boiling water) by day. In other words, the surface doesn't get much heat from below. A few billion years might just not be enough for it to cool out completely.
They both orbit themselves, according to your theory.
Hint: try actually reading what you wrote above instead of being such a smug smartasss for once.
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
the moon is in orbit around the sun and the moon at the same time.
See, that would >imply that the moon revolves around itself, hence the joke.
So all we have to do is build a drilling thingy, go down to the core and restart its rotation with nukes a la The Core. Presto, livable moon and no more city destroying earthquakes, right?
Before the discovery of radioactivity it was estimated that the Earth would only take 20MA to reach its current temperature from a fully molten state. So the internal heat is almost entirely radioactive, meaning that the degree of molten-ness depends mostly on composition, not square-cubiness. Also, exotic is when you use an endangered macaw not a chicken.
It's a layer of cheeze whiz!
If the sun was exerting a greater tidal effect then how come it keeps the same side facing Earth?
The sun doesn't and your observation is correct. But for heating purposes, the Moon is almost static with respect to the Earth. There's a little rocking, but nothing significant. On the other hand, the Moon's orientation with respect to the Sun is still effectively a rotation every four weeks. So even through the Earth's tidal force is much stronger, the Solar tidal forces probably contribute more to internal heating. I could be wrong about this since I haven't given it a great deal of thought, and the Earth's tidal forces may be providing much more heating than I expect.
What about the same reason that keeps the inners of the Earth warm : nuclear fission ? After all, the kaguya probe has found decent amounts of it on the moon's surface (one of the most underrated science news of the recent times, imho) so it is not far fetched to imagine it containing a decent proportion near its core. Especially if it is liquid.
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First sand traps, and now there's even a liquid outer layer on the moon? Man, that's gotta mess with anybody's golf handicap!
Of course it's fluid. What do they think the Whalers sail on?
Now, what is needed is to check to see if Mars has a Molten core. If so, then we have our power to colonize it.
The absence of a planetary wide magnetic field on Mars is a negative indicator. There still be a hot core even if it isn't molten. So plenty of geothermal energy.
> 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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It requires a core that was molten at one point. The number of impact craters covering those features indicate there hasn't been a volcanic eruption on the moon in a long time.
There is no (more) kneading because the Moon is tide-locked to the Earth. Any deformity is permanently fixed in place.
Yes, I totally agree. It did bother me too. But the general consensus seem to be that they are much older, which is why the are underlying the craters, not the other wat around.
What was the age of those Mares then? IIRC, the general view was that they are so old that they 'froze' around the birth of Jes, err, The Earth.
But, this molten core could mean the mares are much younger, I guess!
It's obvious that the OP was talking about compression on the moon from tidal forces, not just tidal force. Since the moon is in tidal lock with the earth this is basically zero for earth. And since tidal forces actually follow an inverse-cube law, not inverse-square, the tidal compression from the sun is not really worth mention either.
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But then, if the moon really is formed out of stuff from earth (which contains a lot of iron ore), and it *does* have a liquid core (making that iron spin) - then why does it not have a proper magnetic field ? Is its rotation too slow ?
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flat. it has mountains and valleys that dwarf anything here on earth, however it doesnt have huge oceans covering huge depths, or huge mountain ranges that go half a continent, like here. its appalling that you talk about mountains and valleys yet forget huge oceans that have 11,000 m as their deepest point in a hole that covers almost half of the planet on one side, not to mention others in other oceans. its not just a mountain, it is a huge inward landscape on all sides of the planet, and outer protrusion on other. take oceans off of the earth in your mind's eye, then rethink.
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Wrong: see Libration
A smaller planet cools faster.
All else equal, sure. But if one of those layers is insulative (at least compared to the larger neighbors) then all bets are off. The Moon is known to be less dense than the Earth, so you would expect the rate of thermal transfer to be less.
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The rate of heat production is proportional to volume while the rate of heat loss is proportional to surface area
...as well as density and the density and temperature of the neighboring material.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Tidal forces from the Sun upon the Earth are sufficient to be noticed and a significant factor when calculating what the daily high tide is going to be, and its impact can usually be measured on the order meters in tidal height on a daily basis. I consider that to be substantial.
The Moon is for all practical purposes at the same distance, although a bit smaller so the tidal forces from the Sun will be reduced... not due to the distance from the Sun itself but rather the sheer size of the Moon. And the Moon is still a pretty big place... we aren't talking something the size of Phobos or some other insignificant rock... the Moon does exhibit hydrostatic equilibrium and is on the same order of size as places like Ganymede, Callisto, Io, and the other largest bodies in the Solar System. IMHO it ought to be classified as a dwarf planet.
But if you consider that the average distance to the surface (for heat conductivity) also increases with R - making it even worse for smaller bodies.
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What's that, the semiautolunacentric model?
You know, it sounds crazy... but with a few epicycles, it just might work...
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