The Moon’s Mantle Muddle

6 Responses to The Moon’s Mantle Muddle

1. gbaikie says:

   April 6, 2014 at 3:52 am

   It seems the lunar crust is deep. But depends on definition and it seems there is different definition of lunar crust than Earth crust.
   Wiki says about Earth mantle “The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density.” And:
   “It is predominantly solid but in geological time it behaves like very viscous liquid.:”
   http://en.wikipedia.org/wiki/Mantle_%28geology%29

   So it seems to me, if on earth, if one somehow remove section of earth crust, you would exposing hot interior rock. Or if one drills 5 km under the surface one will have fairly warm rock.
   So, if want “geothermal energy” on the Moon, how far would you need to drill. Is there anywhere on the Moon where it be is would less than 5 km?
   And there seems limit to how far one drill on Earth, we have not reached it, but anything more than 20 km might nearer it, whereas it doesn’t seem that one reaches same limit at 100 km deep.

   Or perhaps one say it this way, present conditions on Earth defines earth’s crust and mantle, whereas it seem with Moon it may be referring to a distant time in the past [a billion plus years ago]. And if this is true, the crust/mantle of Moon could dependent on time. So 1 billion years ago to present you have crust which was different than crust 2+ billion years ago.

   It seems I remember reading about how the Moon has fractured crust. And seems to me that at some deep it stops being fractured and at such point it could be boundary of lunar layer.
   • Paul Spudis says:

     April 6, 2014 at 5:34 am

     So, if want “geothermal energy” on the Moon, how far would you need to drill. Is there anywhere on the Moon where it be is would less than 5 km?

     About 1000 km — that is the estimate of the current thickness of the lunar “lithosphere” (i.e., the rigid, cool outer layer of the Moon.) On both Earth and Moon lithosphere/asthenosphere is not the same as crust/mantle. The former is a mechanical boundary, based on material strength while the latter is a chemical/mineralogical boundary, based on composition.
2. gbaikie says:

   April 6, 2014 at 5:59 pm

   -On both Earth and Moon lithosphere/asthenosphere is not the same as crust/mantle. The former is a mechanical boundary, based on material strength while the latter is a chemical/mineralogical boundary, based on composition.-

   Ok, And lunar crust refers to latter. A stratification of rock due to cooling of the Moon.
   And I suppose, the assumption or default position until proven otherwise, is the Moon formed from a collision with proto-earth. and that it was closer to Earth and began as molten ball which cooled and might have re-heated from large impactors near the point of time the Moon as molten ball was solidifying, and as solidification continued the latter larger impactors may only partially re-melted large regions [rather than approaching a global effect].

   And it seems at point of enough surface had cooled so as not having partial re-melting
   via large impactors one dealing with time of lunar crust formation.
   Was Moon tidally locked before the lunar crust formed?
   • Paul Spudis says:

     April 7, 2014 at 2:02 am

     A lot of the details of the Moon’s earliest history are still subject to debate, including its origin. It is fair to say that we have a variety of strong evidence for a “magma ocean” stage (which created crust and mantle) and subsequent cooling over the first 500 million years or so.

     The Moon’s synchronous rotation was established very early, but exactly when is not clear. It most likely occurred after the Moon had completely solidified.
3. lroimages2 says:

   April 7, 2014 at 11:26 am

   I wonder how all this relates to the other lunar minerals mentioned in this article….
   http://www.bbc.com/news/science-environment-26696856

   It sounds like there is alot of uncertainty involved in lunar minerals and I would appreciate you lending your expertise to discussing the above referenced article since it is an update to prior work.
   • Paul Spudis says:

     April 7, 2014 at 1:09 pm

     Not much. The apatite grains discussed in that BBC article are found in lunar plutonic (deep-seated) rocks that formed early in the Moon’s history (prior to about 4.2 billion years ago). Water, while present in the lunar interior in greater quantities than had been believed previously, was still a very minor component of the mantle. In any event, these magmas probably came from very deep (~100’s km) levels, much deeper than the 50-80 km depths sampled by the largest basins.

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