Explanation for Lunar Maria (??)

[Widdekind]

Is this a physically plausible scenario (??) — please comment

 

In the Lunar geologic [Lono-logic??] timescale, the "Early Imbrian Epoch" (3850 - 3800 million years ago*) is associated with the Late Heavy Bombardment, and the resulting huge impact basins, which would later fill w/ lava to form the Lunar Mare, during the ensuing Late Imbrian Epoch (3800 - 3200 million years ago). This happened when "the mantle below the lunar basins partially melted and filled them with basalt"**.

*

Early Imbrian - Wikipedia, the free encyclopedia

**

Late Imbrian - Wikipedia, the free encyclopedia

Now, it is well-known that the Moon first formed roughly 15 times closer to Earth than its present orbit today*. And, that early Moon was not, yet, Tide-Locked to the Earth. But, by the present period, not only is the Moon Tide-locked to the Earth, but it's whole inner iron Core has shifted Earthwards inside the Moon, thinning the Crust & Mantle on the Near Side, while thickening the same on the Far Side**.

*

National Geographic Channel

Naked Science — Moon Mysteries

(TV)

**

Carroll & Ostlie.

Introduction to Modern Astrophysics

[1st ed.], pp. 800-801.

 

"Only one

Mare

was seen on the side of the Moon furthest from the Earth. This is not b/c collisions were preferentially occurring on just one side; rather, the

Crust

is actually thinner on the

Near Side

. Consequently, impacts on the thin-crust side were more likely to penetrate the

Crust

, allowing interior molten rock to flow over the surface. B/c the

Crust

is less dense than material in the Moon's interior, tidal forces have caused the heavier

Near Side

to permanently 'hang down' toward Earth" (Carroll & Ostlie,

ibid

.).

 

 

 

CONCLUSION: We must explain why, during the Late Imbrian Epoch (3800 - 3200 million years ago), impact basins on the Moon's Near Side flooded with lava, when the Mantle beneath them suddenly heated & melted. But, we have seen, that once the Moon became Tide-locked to the Earth, its whole inner iron Core migrated towards the Earth — and the Near Side surface. And, moving all that hot material towards the Near Side surface could easily explain the melting of the overlying Mantle, and subsequent flooding of the Mare.

 

This strongly suggests, that by about 3800 million years ago, the Moon had become Tide-locked to the Earth — even as deep basins had been punched into the Lunar surface from the Late Heavy Bombardment. And, over the next 600 million years, the Moon's inner iron Core migrated ever Earth-wards, continually melting the ever-thinning over-lying Mantle on the Near Side, which then flooded the Near Side surface basins with basalts, making the Mare.

 

Indeed, in essence, once the Moon became Tide-locked to the Earth, the Moon's molten inner Core almost melted its way through the Moon, towards the Earth (!!). Had the Moon been bigger, and hence hotter for longer, perhaps the Moon's molten Core could have melted out of the Moon, and fallen back down towards the Earth (!!).

[vordhosbn]

Wouldn't centrifugal force keep it on the moon?

[D H]

Is this a physically plausible scenario (??) — please comment

No, it is not plausible. Comments follow.

 

 

But, by the present period, not only is the Moon Tide-locked to the Earth, but it's whole inner iron Core has shifted Earthwards inside the Moon, thinning the Crust & Mantle on the Near Side, while thickening the same on the Far Side

The giant impact hypothesis naturally leads to an asymmetric distribution of crustal material. The lunar magma ocean crystallized fairly quickly (~100 million years) after formation. That quick crystallization meant the crustal material did not have time to spread over the surface uniformly. The center of mass of the Moon's crustal material is about 2 kilometers from the Moon's center of mass. On the other hand, the Moon's core is quite close to the Moon's center of mass.

 

In short, you are reversing cause and effect here.

 

 

We must explain why, during the Late Imbrian Epoch (3800 - 3200 million years ago), impact basins on the Moon's Near Side flooded with lava, when the Mantle beneath them suddenly heated & melted.

Explaining weird phenomena is always a good thing to do. Doing so with unfounded speculation is not a good thing to do.

 

But, we have seen, that once the Moon became Tide-locked to the Earth, its whole inner iron Core migrated towards the Earth — and the Near Side surface.

That is a huge unsubstantiated leap. We haven't seen that, let alone have you demonstrated that. The rest of the post makes further unsubstantiated leaps on top of this huge one.

 

 

Indeed, in essence, once the Moon became Tide-locked to the Earth, the Moon's molten inner Core almost melted its way through the Moon, towards the Earth (!!).

First off, the two kilometer separation between the Moon's geometric center and the location of the core does not qualify as "almost melting its way through the Moon". Secondly, that two kilometer separation is primarily due to the asymmetric shape of the Moon's crust rather than motion of the core.

 

 

Had the Moon been bigger, and hence hotter for longer, perhaps the Moon's molten Core could have melted out of the Moon, and fallen back down towards the Earth (!!).

Nonsense.

[Widdekind]

The giant impact hypothesis naturally leads to an asymmetric distribution of crustal material. The lunar magma ocean crystallized fairly quickly (~100 million years) after formation. That quick crystallization meant the crustal material did not have time to spread over the surface uniformly. The center of mass of the Moon's crustal material is about 2 kilometers from the Moon's center of mass. On the other hand, the Moon's core is quite close to the Moon's center of mass.

 

Can you cite your source for that figure please?

 

Also, any asymmetry could only have arisen after the Moon became Tide-locked to the Earth, yes ? For, the Moon's ceaseless spinning, before that point, would have continually redistributed any burgeoning asymmetry. Only after the Moon's Earthward face was fixed, would the Moon have started to "sag" into its asymmetric shape, yes ?

[D H]

Can you cite your source for that figure please?

You should have researched this before you speculated that "the Moon's molten inner Core almost melted its way through the Moon, towards the Earth."

 

Doing your research for you,

 

http://www.nature.com/nature/journal/v287/n5782/abs/287520a0.html

The compositional asymmetry between the nearside and farside of the Moon and the natural remanent magnetism (NRM) of lunar rocks are poorly understood. The compositional asymmetry is indicated by the 2-km offset towards the Earth of the centre of mass relative to the centre of figure and the concentration of both KREEP and mare basalts on the nearside.

 

You can find this 2 km offset cited again and again in the scientific literature. While scientists still vigorously debate the cause of this offset, the nature of the offset is well-known.

 

Also, any asymmetry could only have arisen after the Moon became Tide-locked to the Earth, yes ?

Not necessarily. The easier explanation is that the Moon became tidally locked after the the asymmetry appeared. The lunar magma ocean crystallized fairly rapidly, 100 million years or less. The crust took even less time to form, ~61 million years.

 

http://www.nature.com/ngeo/journal/v2/n2/abs/ngeo417.html

http://www.psrd.hawaii.edu/Mar09/magmaOceanSolidification.html

 

 

For, the Moon's ceaseless spinning, before that point, would have continually redistributed any burgeoning asymmetry.

You are positing a differential spinning of the Moon and some transport mechanism to move material from one side of the Moon to another. What makes you think this?

 

Only after the Moon's Earthward face was fixed, would the Moon have started to "sag" into its asymmetric shape, yes ?

Not necessarily.

 

You have not made any claims for the lunar tidal locking time. This needs to be less than the 61 million years it took for the Moon's crust to form to justify your claim. An easy alternative: The Moon is asymmetric because it formed from an asymmetric mass distribution and cooled so quickly that that initial asymmetry became frozen. The Moon is somewhat random because it was born that way.

 

http://www.springerlink.com/content/l2652w08h5l28513/

[michel123456]

The Moon seems to have been tidaly locked extremely quickly. Why is not the Earth tidaly locked to the Moon?

 

" It was challenged by the physicist Harold Jeffreys who calculated that the magnitude of tidal friction required would have quickly brought the Earth's rotation to a halt long ago." from http://en.wikipedia.org/wiki/Plate_tectonics#External_forces

[Sisyphus]

The Moon seems to have been tidaly locked extremely quickly. Why is not the Earth tidaly locked to the Moon?

 

" It was challenged by the physicist Harold Jeffreys who calculated that the magnitude of tidal friction required would have quickly brought the Earth's rotation to a halt long ago." from http://en.wikipedia.org/wiki/Plate_tectonics#External_forces

 

That quote is an argument for why a westward tendency of plate tectonics is not a result of lunar tides. As in, that can't be the cause, because that much tidal friction would have locked the Earth, and the Earth is not locked.

[michel123456]

That is not exactly what I expected as an answer to my question, but I learned something today. Thank you.

[D H]

I've search for the Moon's tidal locking time without success.

[michel123456]

Yes, lack of reliable source. I have been influenced without checking, really sorry.

I just found the following on another forum, no source cited:

"As an example, some tidal lock times :

Moon tidally locked to Earth...............< 7 million years

Callisto tidally locked to Jupiter...........66,000 years

Iapetus tidally locked to Saturn............556 million years

Oberon tidally locked to Uranus............400,000 years

Dysnomia tidally locked to Eris.............66 million years"

 

And from http://209.85.229.132/search?q=cache:http://zebu.uoregon.edu/ph121/l10.html

 

"The age dating of the lunar rocks have allowed us to identify four distinct periods in its geological history:

The moon solidified and cooled 4.4 billion years ago

Between 4.4 and 4.2 billion years and intense period of bombardment occured from the material that was left over from the acretion process. Most of this material was chunks of rock less than 10 km in size.

By now the moon is tidally locked to the earth. At 3.9 billion years there was another period of bombardment which involved a few large (> 100 km) pieces of debris. The earth acted as a gravitational focussing mechanism which caused most of these impacts to occur on the side of the moon always facing the earth (there are no lunar maria on the far side of the moon).

These large impacts produced the lunar maria. This was a severe shock to the crust of the moon and over time, molten basalt would flow out of the deep fissures and cracks in the crust that were caused by the initial impact. This took 200 million years to occur and is the last geological process which occurred on the moon."

 

I suppose data & calculations can be found into P.Goldreich's "History of the lunar orbit." not available to me.

http://ntrs.nasa.gov/search.jsp?R=990408&id=5&as=true∨=false&qs=Ns%3DHarvestDate%257c1%26N%3D4294944087

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Merged post follows:

Consecutive posts merged

Found this:

"The moon has oriented itself so that its heavy side with much more extensive maria, which we know as the near side, is oriented towards the Earth.

 

This is misleading. The moon would have tidally locked to the Earth fairly quickly (probably less than a thousand years). However, the maria would likely have formed over a longer period. In other words, by the time the maria formed, the moon would already have been tidally locked. To imply that the maria formed before the moon tidally locked is misleading at best and factually inaccurate at worst."

from Timescale for tidal locking in http://en.wikipedia.org/?title=Talk:Tidal_locking

[D H]

Found this: ... http://en.wikipedia.org/?title=Talk:Tidal_locking

Wikipedia is not quite a reliable source. The discussion page on a wikipedia article is double so.

[michel123456]

Yes. Lack of reliable source.

[Widdekind]

Not necessarily.

 

You have not made any claims for the lunar tidal locking time. This needs to be less than the 61 million years it took for the Moon's crust to form to justify your claim. An easy alternative: The Moon is asymmetric because it formed from an asymmetric mass distribution and cooled so quickly that that initial asymmetry became frozen. The Moon is somewhat random because it was born that way.

 

http://www.springerlink.com/content/l2652w08h5l28513/

 

(Thanks for the ref !)

 

According to Carroll & Ostlie (op. cit.), the Moon's crustal structure is not random -- rather, there is a strong general trend, of increasing crustal thickness, from the Near Side to Far Side.

 

According to the article you cited:

Ransford and Sjogren (1972) first presented such a model with a

small (R ~ 700 km) core shifted 466 km toward the Earth

, and Kaula et al. (1972) later pointed out that an offset crust, that is, a lower density outer shell thicker on the lunar farside than the nearside, could also account for the offset.

My original suggestion seems in complete accord with Ransford & Sjogren (1972), whose model makes the Moon's core ~2.6x closer to the Near Side surface [572 km] than to the Far Side surface [1504 km].

 

Furthermore, your cited article certainly seems to say that the thinner crust, on the Near Side, could account for the Maria impact basins:

The'offset crust' solution may be supported by both the more easily postulated physical processes that could account for such a state and the fact that the vast majority of mare and lava-filled craters are located on the hemisphere facing the Earth, where

the crust would be thinner and a large impact more likely to crack through to a region of molten mare source material

.

Thus, the combination of a thinner Near Side crust, along with with a hotter mantle "region of molten mare source material", b/c of a moderate core migration (~466 km), could explain the presence of the Moon's maria. Indeed, if some process (presumably Earth's gravity) could completely skew the shape of one Lunar layer (crust), it could conceivably affect lower-lying layers as well (mantle, core).

 

However, if the Moon's crust is actually random, in its various distributions, that lack of any "Earth oriented" global structure to the Lunar crust could mitigate against any similar such structures to lower-lying Lunar layers (core). It does not seem possible to reconcile M.Kobrick's article, w/ Carroll & Ostlie's text & figure. Which one is a more accurate picture ?