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Moon NASA Space Science

The Moon Has a Fluid Outer Core 127

Posted by Soulskill
from the marshmellowy-filling dept.
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."
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The Moon Has a Fluid Outer Core

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  • Wow (Score:5, Funny)

    by Anonymous Coward on Saturday January 08, 2011 @06:23PM (#34808170)

    Molten cheese?

    • Re:Wow (Score:4, Insightful)

      by Pharmboy (216950) on Saturday January 08, 2011 @06:33PM (#34808324) Journal

      More like a chocolate covered cherry.

    • by Anonymous Coward

      Molten cheese?

      Fondue?

    • by spinctrl (815494)
      Fondue.
    • by fishexe (168879)

      Molten cheese?

      That's a long way to dig to get your fondue. Even less worth it if your plan is to make nachos.

    • by ross.w (87751)
      It's just a bit runny. Runnier than you'd like it, I'm afraid.
  • by Anonymous Coward

    I thought the solid Moon was a done deal. Was I misinformed, or is this groundbreaking science (forgive the pun)?

    • Re:Amazing stuff (Score:5, Informative)

      by Artifakt (700173) on Saturday January 08, 2011 @09:39PM (#34810264)

      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.

      • by Nyeerrmm (940927)

        We'll hopefully have a lot more data this time next year as well. The GRAIL mission, which will map the gravity of the moon and get a better sense of it's internal structure, is launching in the fall.

        Thanks for your detailed explanation. I'm supposed to start working on that mission soon, and this gave me a much better grasp on the background.

      • Thank you for the very informative post. I was just about post "if it has got a liquid core layer, where's the magnetic field" so thank you also for answering my stupid question before I got a chance to ask it.
      • (Since all the long lasting radioactive isotopes are dense metals).

        The decay of potassium-40 is the major contributor of heat within the Earth. Potassium isn't a dense metal. Also, there is a theory that a significant amount potassium could exist in the Earth's core [physicsworld.com].

        Maybe potassium-40 is the reason why the moon does have a liquid outer core?

      • by perrin (891)
        Nice post. Just thought I'd point out one small mistake -- Mercury does have a magnetic field, despite its tiny size! Even though it is only 1% of the strength of Earth's, it envelops the entire planet and shields it from the solar wind, just like on Earth, and so much unlike the Moon, Mars and Venus.
        • With rotation tidally fixed to the sun, and magnetic shielding to boot, Mercury should have some nice real estate at its hot/cold boundary!

          All you'd need now is oxygen, water, pressurization, mirrors, UV filters, and some frozen food that you keep in the shade of a big crater.
      • by Convector (897502)
        Actually, all the long-lived radioactive elements (K-40, U, Th) are lithophile elements. That means they preferentially bond to silicic compounds. So, while U and Th are heavy metals, they aren't found in their elemental state. They form oxides and stuff and hang out in the mantle. There won't be much radioactivity in the core. Futhermore, these elements are among the first things to melt when mantle rocks are heated, so they preferentially go into the crust. So, if anything, we'd expect the moon to h
  • I was hoping for caramel.
    • I was hoping for caramel.

      It's "candy-coated popcorn, peanuts and a prize."

      Buzz Aldrin already got the prize, so if you plan to visit the Moon, don't be disappointed when you can't find it.

      When he was confronted by one of those Apollo Moon landing hoaxer kooks, who screamed, "Show us the prize!", the 70+ years old Aldrin responded by knocking the kook's teeth out.

      If I ever meet Aldrin in a bar, I'm buying.

      • by Tetsujin (103070)

        I was hoping for caramel.

        It's "candy-coated popcorn, peanuts and a prize."

        Buzz Aldrin already got the prize, so if you plan to visit the Moon, don't be disappointed when you can't find it.

        Not only that, but they ate all the peanuts...

  • 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.

    • by AfroTrance (984230) on Saturday January 08, 2011 @08:50PM (#34809868)

      Incorrect. Elements segregate in the Earth (and Moon) based on chemical affinities [wikipedia.org], 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).

      • So what happens if or when we mine enough Uranium from the Earth? Would the drop in radioactive heat allow the core to cool significantly faster, or is it just a redundant heat source? I'm working on the assumption that, even if we did mine out all the Uranium, the core wouldn't cool down fast enough to matter to anyone with an average human life span, but all the same I'm curious just how much of a cooling impact there would be.
        • To correct/or add to my previous point, most of the heat generated would be from the mantle and core, not the crust. Even though uranium etc are more concentrated in the crust, the much higher volume of the mantle/core negates this. Also, other elements provide heat through radioactivity, such as thorium and potassium-40.

          Finally, we can't mine all the uranium. It's only profitable to mine highly concentrated uranium, close to the surface. How concentrated or deep will change in the future as demand increase

          • Actually, I was reading up on it, and some sources say half of the heat comes from the crust, while others say most comes from the mantle/core.

            • by M8e (1008767)

              The difference between those two statement could be really really small.
              One say 50% from the crust. The other says more then 50%(50.01%?) from the mantle/core.

              Did anyone of those sources say something more informative than "most"?

      • by drinkypoo (153816)

        Incorrect. Elements segregate in the Earth (and Moon) based on chemical affinities, not on weight.

        The mantle is below us and mostly made out of heavy elements, or at least it contains a higher concentration thereof. It's probably safe to say that elements segregate both due to weight and chemical affinities. It's not like uranium is going to jump up off the soil if you hold some rocks over it. This characteristic is more produced in the mantle than the crust, probably due to melting effects.

    • And somewhere in between the surface and the core is a temperate zone where water is in its liquid phase. Since we have found life in every environment on Earth where water is liquid, we need to assume that there is some kind of thermal driven ecosystem inside the Moon.

      Are there selenites? Possibly so. I hope the lunar exogeolists are talking with the biologists who have been studying our black smokers.

      • by MichaelSmith (789609) on Sunday January 09, 2011 @02:49AM (#34812390) Homepage Journal

        Check out the temperature at 2 metres depth [nasa.gov]. 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.

        • I do not understand the parent comment, and do not see the relevance of the reference provided there.

          The closest I got was in Chapter 5 of the reference where Apollo 17 found a temperature close to 256 K at a depth of 2 meters [nasa.gov] (scan down the page to the second chart insert). This is less than 2 degrees Fahrenheit, and at that shallow depth is probably around the average annual temperature of the surface, as in Earth caves. There is no reason not to expect the temperature to continue to decrease for many m

          • Sorry I should have been more specific. I was looking at Figure 06 which shows temperature increasing at roughly 0.02 degrees C per centimetre of depth. Another 40 degrees gets you to 300 Kelvin at ~20 metres depth. But the moon is pretty much gardened to that depth in the sense that meteors dig craters that deep and turn the surface over. So if there was water at 20 metres at one time it is unlikely to be there now, except at the poles which are very cold.

  • 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.
    • Re:And yet, (Score:5, Interesting)

      by icebike (68054) on Saturday January 08, 2011 @06:48PM (#34808514)

      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.

      • Re: (Score:3, Interesting)

        by unity100 (970058)
        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
        • Very interesting point when in considering that in proportion to it host planet (huge ration actually!!), its the largest moon in sol, and as thus, having the most influence over its host planet, with the most important force at play with bodies this big - gravity.
        • Re:And yet, (Score:5, Informative)

          by BradleyUffner (103496) on Saturday January 08, 2011 @09:14PM (#34810068) Homepage

          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.

          • by dkf (304284)

            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.

            Maybe he's basing it on some of the pictures that have been sent back (though obviously not the ones of inside a crater) which have mostly been from fairly flat locations as they're easier to land safely in and get good scientific results back from.

          • 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 protrusio
            • 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.

              The height of Olympus Mons I have is height above Datum. Mars has deep basins that go far below datum also.

              From Wikipedia:

              "Since Mars has no oceans and hence no 'sea level', it is convenient to define an arbitrary zero-elevation level or "datum" for mapping the surface. The datum for Mars is defined in terms of the height at which the air has a particular pressure at about the freezing point of water: a pressure of 610.5 Pa (6.105 mbar), approximately 0.6% of Earth's, at a temperature of 273.16 K. This pre

          • Relative to it's diameter, yes, it is flat [blogspot.com]. Though it's a bit rougher than earth's crust.
        • Re: (Score:2, Insightful)

          by Anonymous Coward

          Hail to the Great Spaghetti Monster in the Sky, he hath done a greate jobbe!

        • by ultranova (717540)

          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.

          The temperature difference between night and day grind moonstones to dust. So do the very meteor collisions you mentioned. And lack of tectonic or volcanic activity means there's no new mountains being rised, so of course the end result is a flat, dust-filled world.

          • by unity100 (970058)
            its so easy to justify. thats the problem of contemporary science. very easy to produce half assed explanations for everything.

            that half assed one, for example, fails on the face of the fact that there are even greater forces, be it temperature difference, or others, acting on other planets and moons. yet no planet is such finely grained into sand.
            • by dizzydogg (127440)

              Many of the other large bodies is space are more mountainous and uneven specifically because of the fact that they have much greater forces applied to them on a regular basis. Those forces are not evenly distributed across the planet, and cause mountains to rise from tectonic pressure and valleys to be carved from 100km/h sandstorms. The moon has no volcanic activity to create new mountains, and no atmosphere/rain to erode valleys, and as such the only real surface details are the overlapping craters left

        • there is a reason why they are that flat, and uniform. there is something grinding the stones to sand.

          The variation in a planet's crust (from mountains to trenches) are tiny compared to it's diameter (less than a percent).
          Sure atmospheric conditions contribute a bit by grinding down mountains a mile or two, but most of the flatness of rocky planets is caused by gravity and hydrostatic equilibrium.
          Meaning that molten rock tried to form a spheroid (a bit bulgy at the equator due to rotational forces), simi

    • Re:And yet, (Score:4, Insightful)

      by Kenja (541830) on Saturday January 08, 2011 @06:53PM (#34808606)
      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.
    • Is that what you are saying?

    • by Anonymous Coward

      Fantastic as it is, here is absolute, undeniable proof that humans created the moon: Who built the Moon? [mental-magic.com]

      Case closed.

  • by Anonymous Coward

    Arthur C. Clarke had a novel where they used the molten moon core as a weapon against spaceships.

    • In Earthlight, yeah. I reckon you could build a good city on the moon around a drill to the lunar outer core. Should be possible to recover energy and useful elements from that depth.

  • What's a cthulhu? fhtagn...wha?
  • by Anonymous Coward

    There have been discussions of a probe to Uranus [nationalgeographic.com]. 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.

    • by Anonymous Coward

      Goddamned Frenchmen are always trying to pull this kind of stuff.

  • by jhobbs (659809) * on Saturday January 08, 2011 @07:54PM (#34809300)
    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?
    • by lennier (44736)

      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?

      And that's how we get to the future scenario in the movie version of The Time Machine.

    • I was thinking of the same but we can't do that even if it was easily feasible a-la-Unobtanium.
      If the moon had a magnetic field it would either be attracted to or repelled from the earth.

      IOW: The moon would eventually crashes into the Earth or we would have a "Space 1999" scenario where the moon leaves the earth.

      If someone knows what is the centrifugal force on the moon keeping the gravitation force at bay are, I'd love to know that I'm wrong.

  • It's a layer of cheeze whiz!

  • for everybody!
  • 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?
  • 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 ?

    • by Convector (897502)
      It's not enough for the iron to be molten. The fluid also has to be moving turbulently to generate a magnetic field. This is accomplished either by the core being cooled from above or by the core freezing at the center. If it's not cooling fast enough, you don't get dynamo activity.

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