New Study on Lunar Core

[renormalised (Carl)]

Seems the Moon has a small amount of liquid in its core....

http://www.nasa.gov/centers/marshall.../H-11-004.html

New studies of old Apollo data seem to indicate that the core of the Moon is more complex and dynamic than once thought. It appears that surrounding a dense solid iron core of about 300 miles diameter, there is a molten zone that extends out to 400 miles (making it 100 miles deep). Then there is a partially molten zone out to 600 miles and then solid mantle out to the crust (Picture courtesy of NASA/Renee Weber).

[CraigS]

Hmm … interesting one, Carl;

I thought that rotating liquid metal (iron) in the core of a moon/planet usually generates a dipolar magnetic field. I think the moon only has localised crustal magnetic fields - not dipolar (??)

Interesting ..

Cheers

[renormalised (Carl)]

Originally Posted by CraigS

Hmm … interesting one, Carl;

I thought that rotating liquid metal (iron) in the core of a moon/planet usually generates a dipolar magnetic field. I think the moon only has localised crustal magnetic fields - not dipolar (??)

Interesting ..

Cheers

The fact that the Moon rotates so slowly probably precludes most turbulent motion within that liquid part of the core, so it doesn't generate a magnetic field. Much the same sort of situation Venus is in.

Any motion in the liquid is probably vertical motion (very slow convection), which would tend to dampen down the formation of a field.

[CraigS]

Originally Posted by renormalised

The fact that the Moon rotates so slowly probably precludes most turbulent motion within that liquid part of the core, so it doesn't generate a magnetic field. Much the same sort of situation Venus is in.

I suppose so … (as per the evidence in hand).
Looks like this study provides us with another data point about rotation, (or lack thereof), and volumes of molten iron in the core.

Originally Posted by renormalised

Any motion in the liquid is probably vertical motion (very slow convection), which would tend to dampen down the formation of a field.

… or disrupt temporary emerging fields, resulting in an overall 'neutral' field (cancellation).
There's something about chaotic motion on these scales to learn from these measurements, I reckon.

Cheers

[renormalised (Carl)]

There's heaps to learn

Might not be any motion in the liquid core at all...they'll need to do more seismic studies to determine that.

[CraigS]

Surely if its hot, there must be motion ??

[Miaplacidus (Brian)]

What's with all the conjecture? Can't they just send Bruce Willis and his team of drillers to find out?

[renormalised (Carl)]

Originally Posted by CraigS

Surely if its hot, there must be motion ??

Depends on how it's being heated. It could be that syrupy thick that it hardly moves at all, or it could be just slowly bubbling away with vertical motion. Depends a lot on what's in the liquid as to what its consistency is going to be like. If it has an appreciable amount of sulphur or oxygen in the core, it'll be fairly fluid. If it's pretty much all iron or iron/nickel, it will be very sticky and gloopy and it would take a lot of heat to generate appreciable currents in the material.

[CraigS]

Carl;

Oh well looks like it won't be long before we find it all out …

Future NASA missions will help gather more detailed data. The Gravity Recovery and Interior Laboratory, or GRAIL, is a NASA Discovery-class mission set to launch this year. The mission consists of twin spacecraft that will enter tandem orbits around the moon for several months to measure the gravity field in unprecedented detail. The mission also will answer longstanding questions about Earth's moon and provide scientists a better understanding of the satellite from crust to core, revealing subsurface structures and, indirectly, its thermal history.

It'll be good to get more data.

I must admit, I secretly harbour doubts about the whole moon origin theory (yep an opinion .. no evidence).

I've been looking at some of the latest Cassini data/picckys and one has to wonder just what forces and process steps actually occur, in the aggregation (clumping) of orbitally floating material, ultimately resulting in something big .. like a moon …
… And then how the heavy stuff like iron ends up in the middle in a molten/liquid state.

I understand the classic explanation .. but data about Saturn's rings should be showing us the real thing. I'm not so sure its obediently following this theory, though

Cheers

[renormalised (Carl)]

Originally Posted by CraigS

Carl;

Oh well looks like it won't be long before we find it all out …



It'll be good to get more data.

I must admit, I secretly harbour doubts about the whole moon origin theory (yep an opinion .. no evidence).

I've been looking at some of the latest Cassini data/picckys and one has to wonder just what forces and process steps actually occur, in the aggregation (clumping) of orbitally floating material, ultimately resulting in something big .. like a moon …
… And then how the heavy stuff like iron ends up in the middle in a molten/liquid state.

I understand the classic explanation .. but data about Saturn's rings should be showing us the real thing. I'm not so sure its obediently following this theory, though

Cheers

Once the material aggregates, a combination of factors heats the body up so that the heavier material sinks to the core of the planet and the lighter material floats to the surface. Most of the heating comes from the impacts of objects into the growing planet/moon and from internal heating caused by gravitational contraction and radioactive decay.

An object the size of the Moon can form very quickly...within a decade or so. A planet like the Earth can take a lot longer....upto 20-30 million years, simply because it's so more massive than a satellite like the Moon.

The reason why Saturn's rings haven't aggregated into a Moon is because of orbital resonances between the particles and the gravitational influence of the planet itself. Although they're not all that old, probably only a few tens of million years old. They'll eventually dissipate and/or aggregate into a moon or two. Whether they survive could be problematical.

[CraigS]

Originally Posted by renormalised

Once the material aggregates, a combination of factors heats the body up so that the heavier material sinks to the core of the planet and the lighter material floats to the surface. Most of the heating comes from the impacts of objects into the growing planet/moon and from internal heating caused by gravitational contraction and radioactive decay.

Yep. Gotta wonder how much effect the mutual tidal tugs between the Earth and the Moon has on the Moon's inner temperature.
I mean, there's a big effects resulting on the Earth (oceans tides, etc). I've never really read anything about what effect folk think it may have on the Moon, though. (Apart from orbital mechanical stuff).
… I mean it has a huge inner temperature effect on the closer in moons of Jupiter and Saturn, where big-time processes result from big-time pulls and electrical discharges etc.

Originally Posted by renormalised

An object the size of the Moon can form very quickly...within a decade or so. A planet like the Earth can take a lot longer....upto 20-30 million years, simply because it's so more massive than a satellite like the Moon.

The reason why Saturn's rings haven't aggregated into a Moon is because of orbital resonances between the particles and the gravitational influence of the planet itself.

Yes … there's all sorts of interesting stuff in the photos from Cassini .. propellers, waves, spokes (magnetic field influence), etc .. wouldn't one expect all this for a debris field, (left over from the impact/collision), around the Earth, also ?
The differences between the two scenarios must emerge at a more detailed level, (perhaps by simulations), than maybe, is revealed from only a rudimentary high level understanding of the Earth impact theory, eh ?

Originally Posted by renormalised

Although they're not all that old, probably only a few tens of million years old. They'll eventually dissipate and/or aggregate into a moon or two.

Yep. They already have those 'shepherd' moons in there, also Pandora, Prometheus, Hyperion, etc.

The diversity of it all, I find overwhelming. I really think the days of one idea/theory-fits-all for planetary/moon formation, is rapidly becoming outdated with the uncovering of all this new information. And I feel this is going to become even more obvious as time goes by .. the physics may stay the same, but the diversity of environments increases the complexity of the physics … (this is just an unsupported view, mind you .. )

Cheers