Internal structure of the Moon?

[Robittybob1]

Moon's Iron Core May Reveal Solar System Secrets with X-Ray Scan

http://www.space.com/28900-moon-iron-core-solar-system-secrets.html

 

I am always finding the Moon formation interesting. Here this article talks about the size of the Inner Core (MIC) and Outer Core (MOC) of the Moon. (I didn't know there was such a thing as a liquid MOC.)

Now with the Moon tidally locked to the Earth is there any suggestion that the MIC is displaced toward the Earth, making the Moon's mass lopsided, and hence "locked"?

[Robittybob1]

Found a first clue: http://www2.astro.psu.edu/users/cpalma/astro10/class21.html

 

The Moon is very different. The average density is 3300 kg per cubic meter, but more importantly, there is less variation in the density from core to crust than the Earth. The Moon is not geologically active -- there are no volcanoes or plate tectonics on the Moon. Equipment left behind by the astronauts that landed on the Moon have detected Moonquakes, but they are very mild. Interestingly, it looks like the core in the Moon is off center. The crust is about 60 km thick on the near side (facing Earth), but it is 150 km thick on the far side. This was probably caused by the gravitational pull of the Earth on the Moon while the Moon was still molten.

So it is not just the MIC that is displaced but the whole inner structure.

 

"NASA Research Team Reveals Moon Has Earth-Like Core" http://www.nasa.gov/topics/moonmars/features/lunar_core.html

has a picture of the internal structure.

 

 

Uncovering details about the lunar core is critical for developing accurate models of the moon's formation. The data sheds light on the evolution of a lunar dynamo -- a natural process by which our moon may have generated and maintained its own strong magnetic field.

The team's findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles. The research indicates the core contains a small percentage of light elements such as sulfur, echoing new seismology research on Earth that suggests the presence of light elements -- such as sulfur and oxygen -- in a layer around our own core.

The researchers used extensive data gathered during the Apollo-era moon missions. The Apollo Passive Seismic Experiment consisted of four seismometers deployed between 1969 and 1972, which recorded continuous lunar seismic activity until late-1977.

So since the Moon has a molten MOC and solid MIC similar to the Earth does the Moon have a magnetic field?

 

It seems that it did in the past: "The lunar dynamo" http://www.sciencemag.org/content/346/6214/1246753.short

 

 

A new generation of laboratory magnetic studies of lunar rocks and spacecraft measurements of lunar crustal magnetic fields have produced major advances in our understanding of the evolution of ancient magnetic fields on the Moon. It has now been established that a dynamo magnetic field likely existed on the Moon from at least 4.5 billion to 3.56 billion years ago, with an intensity similar to that at the surface of Earth today. The field then declined by at least an order of magnitude by 3.3 billion years ago. The early epoch of high field intensities may require an exceptionally energetic power source such as mechanical stirring from mantle precession. The extended history of the lunar dynamo appears to demand long-lived power sources such as mantle precession and core crystallization.x

When did the Moon become tidally locked?

http://en.wikipedia.org/wiki/Moon#Appearance_from_Earth

 

 

The Moon used to rotate at a faster rate, but early in its history, its rotation slowed and became tidally locked in this orientation as a result of frictional effects associated with tidal deformations caused by Earth.

No time period mentioned as yet!

Edited March 27, 2015 by Robittybob1

[Robittybob1]

Does anyone have access to this article?

"Origin and evolution of the earth-moon system" Hannes Alfvén, Gustaf Arrhenius http://link.springer.com/article/10.1007/BF00562115

 

I like what it says in the abstract

 

 

The origin and evolution of the Earth-Moon system is studied by comparing it to the satellite systems of other planets. The normal structure of a system of secondary bodies orbiting around a central body depends essentially on the mass of the central body. The Earth with a mass intermediate between Uranus and Mars should have a ‘normal’ satellite system that consists of about half a dozen satellites each with a mass of a fraction of a percent of the lunar mass. Hence, the Moon is not likely to have been generated in the environment of the Earth by a normal accretion process as is claimed by some authors.
Capture of satellites is quite a common process as shown by the fact that there are six satellites in the solar system which, because they are retrograde, must have been captured. There is little doubt that the Moon is also a captured satellite, but its capture orbit and tidal evolution are still incompletely understood.
The Earth and the Moon are likely to have been formed from planetesimals accreting in particle swarms in Kepler orbits (jet streams). This process leads to the formation of a cool lunar interior with an outer layer accreted at increasingly higher temperatures. The primeval Earth should similarly have formed with a cool inner core surrounded in this case by a very strongly heated outer core and with a mantle accreted slowly and with a low average temperature but with intense transient heating at each individual impact site.

That "cool" formation would logically be a prerequisite to have events like the Iron Catastrophe 500 million years are the formation of the Earth.

[Robittybob1]

There doesn't seem to be a good paper on when the Moon became tidally locked to the Earth.

The fact that the whole inner structure is tidally displaced toward the Earth and the Moon having different topological features on the Near Side compared to the Far Side suggest to me it was a long time ago, and not a recent event, but when?

[Robittybob1]

Considering there is the thread ageing the Earth, one would think the Moon would serve as a better example, to examine how astronomical bodies cool over time.

Small mass, no atmosphere, no oceans to evaporate, and still there is a molten outer core in the Moon, that seems quite incredible, but it must help us work out how it works.