Oh, absolutely, a larger core turning at the same angular velocity will have much greater angular momentum than a smaller one. But remember that as it accretes solid matter from the outer core, it will also gain the outer core material's momentum (and hence, on the macro scale, its angular momentum), which would counter this effect in your scenario, slowing down the angular velocity relative to the mantle.
I think the best analogy I can think of would be a badly broken car brake (or airplane brake, which I know better, but close enough :wink: ). Imagine that your car wheel is spinning frictionlessly in the air, for some reason. Imagine that you then slam on the brakes full force, so hard that the brake calipers (we're using disc brakes here) break off and weld themselves onto the rotor. Yes, the moment of inertia of the wheel + rotor + caliper will certainly be greater than wheel + rotor was, but the angular momentum will be conserved, so the whole thing will have less angular velocity than the wheel + rotor did before, the wheel + rotor will have less angular momentum than before, but the caliper will have much more angular momentum than before (since it previously had 0 kg*m^2/s).
Basically, it won't be able to expand by accumulating formerly molten matter onto itself without its angular velocity becoming closer to that of the molten matter. The overall effect on angular momentum could be an increase or a decrease (in the analogy, if the caliper had been spinning the other way, the angular momentum of wheel + rotor + caliper could be less in magnitude than wheel + rotor was), but there certainly won't be a direct r^5 increase in angular momentum.

Added: This should hold whether the outer core flow were laminar or turbulent.

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Well what do you know, it did help imagining this Big-Hot-Brake scenario for Venus, having some experience with converting roughly some 0.1-0.2 GJ of kinetic energy into heat into two of those tiny brakes on a daily basis. Also some significance has the fact that it -in case of over braking- it would take 30-60 minutes before the heat was taken out and the fuses would blow. Since Venus is still very hot after say 500 million years.

I agree but may I take the liberty to question that scenario for Venus, if the calipers would resemble that part of the liquid outer core that solidifies to the inner core.

Indeed the start value of the angular momentum of the calipers is zero but the momentum of liquid outer core most certainly is not. We may assume that the overall angular velocity of the highly turbulent outer core resembles already a starting value consistent with the spinning of the planet, not zero at all. Consequently each and every particle that attaches itself to the solid inner core also transfers its particular angular momentum to that inner core.

Now since that process of attaching also implied getting a bit closer to the centre of the planet and hence assuming a slightly smaller radius, it needs to spin up slightly to preserve the angular momentum. Consequently the inner core will spin up like the ice skater, when it grows. And we see that on Earth as I stated.

Next planned is the contradiction between Correias spinning down model and NASA's wet greenhouse model.

About the big brake on Planet Earth. I propose that it has started roughly 0,9 million years ago. Certainly, nothing is happening right now, all the spinning axes are aligned nicely but it may have been different in the recent geologic past and the signs are all over the place. But since we did not recognise them, unaware of the mechanism, we call those signs the "Ice Age".

Nice header for the papers: Hot Brake Causes Ice Age.

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Ok forget about that. I'll be maxed out next week So a little bit of background history now to keep the thread going.

The first against-the-mainstream ideas is the Looney tune- scenario of Velikovski

The debunking of this seems to have been a big circus in which the role of word famous Carl Sagan was under debate.
Also: http://abob.libs.uga.edu/bobk/velidelu.html

The scenario of Velikovski called for a hot planet cooling down, whilst Sagan promoted the (runaway) greenhouse gas model. However for the greenhouse model to work the reflectivity (Albedo) of Venus cannot be too high, otherwise the planet would not absorp enough energy. This seems to be a can of worms or not?

Well we're talking about Bad Astronomy. So that would be correct indeed.

Anyway the runaway greenhouse model did not hold according to NASA and the new proposal is the wet greenhouse model.

This calls for a change in the atmosphere:
But Correia needs the Atmosphere for his spin slowing down model as the main force is tidal atmospheric drag. Without dense atmosphere no significant slow down.

Another problem for any greenhouse gas hypothesis would be cracks in the surface BTW. suggesting that it has been a lot warmer in the past. GHG effect would not allow for cooling, I would think.

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Quid est ergo tempus.
Augustinus

That's a nice theory!! Any idea about when this happened?

That theory. Well the big brake hypothesis dates from june 2003. The event itself took many (hundred) million years in total and is manifest when Venus "resurfaced" anywhere between 300-700 million years ago, depending of the source.

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Back for some more.

First, let's check the main problem of Correia et al about their mechanism of stopping the spin of Venus:

The initial spinning of a planet is assumed to be the sum of momentum of all spinning particles in the rotating dust cloud that formed the planet. As the momentum is mass times spin radius and the total momentum is constant, the spinning keeps increasing when the particles approach each other, decreasing the radius when they are building the planet. See para 2.2.4. of
Correia et al Part 2 (pag 5) explaining this

Now I guess you need another basic understanding how the proto planets were build to accept such a deviation between the MacDonald proposal and the maximum acceptable spin for Correia et al. Note that this difference in initial spinning state represents a factor 28 in spinning energy.

In the Big Brake hypothesis, the gravitational interaction with the bulge of a spinning planet should be orders of magnitudes bigger than the atmospheric gravity and so is the exchange of momentum. Hence it may be able to handle the initial spinning state of 13,5 hrs and still end up with the current retrogade spinning.

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Quid est ergo tempus.
Augustinus

Getting quiet here . It is allowed to post in my thread :P .

No more objections agains Venus big brake? Perhaps it is allowed to philosophise a bit about Earths big brake. I know, I'm triggering all your baloney detectors [-X But rest assured; all the evidence is in peer reviewed publications.

Now how would an starting big brake of Earth work. We imagine that it is just beginning as the Earth rotation has not been decreasing very much yet. Let's figur the difference in spin axes again between the Earth mantle and the Earth solid inner core. Image the area of the liquid outer core between the two spin axes. In here the movement of the inner core is opposite the movement of the mantle. It looks like counter rotation but it is not the same. Anyway this counter-movements create a big drag area over there that hampers the normal spinning of the mantle.

What follows is a very complicated process, that I would not try to explain in detail right now, but it results in a force away from both spinning axes that ultimately would result in a wandering tendency of the mantle. The immense moment of inertia of the mantle would tend to resist movement. But the mantle is also elastic, capable of "storing" forces and in the end some wandering of the mantle could happen. We called this the "Rapid True Polar Wander", but I guess Kirshvink used the term first for another mechanism.

Anyway, we think that the evidence of a periodic wandering mantle is currently used to explain Pleistocene ice ages.

But this is an Astronomy board of course. So I'm afraid I can't really discuss this here, but there is plenty more where this is coming from.

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Augustinus

I see, as with Baldrics wine you have an unlimited supply?

spell edit

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Well, if you consider plenty identical to unlimited. But you could dare me of course.

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You've put a lot of thought into it. Why don't you write up a paper for peer review in a geophysics journal?

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Very, very nice. I'll say the positive things first:

The idea of the different rates of precession feels right, and would make things interesting. I like it.

The transfer and shifting of angular momentum about is also very nice.

But I still see problems.

First, lets hit your angular momentum derivation:

I'd leave L as expressed by:

L= 2/5*M*r^2

Why? Because we don't know how the density is behaving really. If we just view it, for simlicities sake, in the more general "mass transfer" idea, we can look at it better.

The core, when it has mass added to it, will slow down. You have to have a very large density change (which I don't see happening) in order to get it to drop that way. So your core actually slows if you put mass onto it.

Basically, we can look at it as:

L=IW, as you stated. But I (due to mass addition, and radius increase) is going to increase. So W must move the other way to keep L constant. Only External effects can change the total angular momentum.

While the cores doing that, the part lending mass is going to lose mass (of course) and speed up. I.e. the higher angular velocity of the core is going to rub against the inner core and speed that up. Both shall move towards an equilibrium.

While the planet radiates heat away, thus causing the entire thing to cool as a whole, the turbulence and friction near the inner core (helped by your differring rates of precession) will provide more than enough heat to keep that section from changing phases between solid to liquid to much.

Now, I also have a general problem with how you are removing the angular momentum from the system. It appears you're doing so by transfering it to the sun (the cause of the precession). Thats fine, but I don't think the rate is high enough to do it in <5 gyr.

[quote="Andre"]Why thank you. First of all I have posted this threads in other fora, I'm sure you can google them up. Anyway a kind reflectant, also a member here I see, suggested to try these boards.

So following is the abstract to the solution of Venus, hang on. I'm not a good narrator and it's not easy and I may have lost many listeners. But anyway I think its worth the try.

IIRC Turbulence actually decreases the efficiency of heat transfer. Laminar flows do a better job (i.e. simple convection). That will help insulate the core.

Basically, while the mechanism may be valid, and have played a part. I still think something had to bleed of most of Venus's angular momentum in the first place.

Oh, and its basically not possible to have a planet accrete from a proto-planetary disk with core going one way, and the rest going the other.

Thanks for your reactions.

Well, the combined effort of three people searching and processing anything related in the fields of Quaternary geology, oceanography, glaciology, palaeo climatology, palaeo Earth magnetism, geophysics, planetary astronomy for a couple of years.

And I might add that those publications average generally one "not understood" and "the results of the tests did not support the hypothesis" while estimated over 90% of those publications seem to support our Big Brake - Rapid True Polar Wander hypotheses.
.

We will, eventually I hope. The whole story with proof in detail would take several issues of journals. A short narrative lacks the elaboration of convincing evidence. But the biggest problem is convincing power. Here are a couple of John and Jane Does knowing-it-all and telling the pros how to do their jobs. I'm not nagging but I have heart this argument not long ago. So like all the other crackpots it’s either baloney or threatening, So it must be wrong, no matter what.

Some discussions if I may:

??

Unless that added mass has it's own momentum added as well. Since the liquid outer core should spin as well with a balanced angular velocity, the average momentum of all the particles in the liquid outer core would be the same if the outer core was solid.

That would only be true if the added mass has less momentum. But again, since the particles average already the required momentum for their radius and they are moving inwards while attaching to the core, the radius decreases and the particle spins up, adding more speed to the solid inner core. But the discussion about a inner core losing or gaining angular velocity would not distract from the general hypothesis. The principle remains the same.

Consider the total momentum of both inner and outer core or L=I1W + I2W or L=(I1+I2)w. Solidifying or liquefying interaction between the inner and outer core only changes I1 and I2. The Sum of both remain constant.

I agree that the momentum relationship is highly simplified. It was only required to show that during the core growth the transfer of angular inertia from the liquid outer core (I1) to the solid inner core (I2) is very large. This should be indicating that the increase of the precession wandering tendency of the inner core happens very rapidly, while decreasing the stabilisation power of the outer core equally large.

That keeps me awake at night :wink:

Incidentally, did you just solve the riddle of Earths interior heat without needing vast amounts of radiogenic material in the core, for which is no supporting evidence?

I have no doubts about that but eventually the convection (laminar or turbulent) in the outer core should transport that heat away from the source.

We sure need a lot of mathematical brain power to model this. That's way above me. But allow me some remarks.

Consider Earth momentum vector L in two components, L* cos(inclination) perpendicular to the plane of the Earth orbit around the sun and L* sin(inclination) within that plane. Now take the same situation in 13,000 years from now, when the Earth has completed a half precession cycle. The horizontal component of momentum is now: minus L*sin(inclination), opposite the original value. Hence an enormous transfer of (vector) momentum has taken place in a mere 13,000 years. Again intuition may not help us here.

I believe it’s alright to toy with crazy ideas as long as you do reality checks. So the Earth – moon transfer of momentum is very significant in the precession cycle. So, what if Venus used to have one or more moon(s) too, required to do a lot of momentum transfer in a relatively short time? When the big brake was active, those moons regressed continuously from their orbits until the orbit became unstable and the sun took it/them over. Could we know that moon already and have named it “Mercury”? I don’t know, just philosophising. Alternately that moon could have been swallowed by the sun. I’m sure there is a lot of brainpower around here to test those wild ideas.

Edit correcting mistakes

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Quid est ergo tempus.
Augustinus

Modern geophysics does not assume that there is vast amounts of radiogenic material in the core. Such material is more concentrated in the crust.

Well, A planets iron inner core may contain radiogenic Potassium-40 (40K)that has been appointed candicate for the core heating, like here

Let's do some quantification.

The relative abundance of 40K (d40K) is 10mil So the effective mass ratio of 40K in the core is 7.10^-8 (assuming no fractionation).

The mass of the core is 1.719 x10^24 kg. So the 40K mass could be 1.2 . 10^-17 kg.

The decay constant is of 40K is 1.2x10-17s-1. (just the same number by shear coincidence). So every second one kg of 40K decays, producing 1,5 MeV per atom.

With 25 mols in the kg the total energy is 25 * 6*10^23 * 1.5 = 2,25.10^25 MeV. Since 1 MeV = 1.60210^-13 J some 1,4. 10^12 J is produced. or 1.4 10^12 watt per second. The current heat loss of the earth core however is about 25% of 44 Trillion watts or 1,1.10^13 watts per second.


That is, if I’m correct about the unsure meaning of “trillion” in the US and elsewhere. So I still seem to be missing about 70% of the required radiogenic material.

Furthermore I can't find out at the moment if 40K is produced in some other radiogenic decay series and if those require additional elements in the core.

Or did I do something wrong. Anyhow It seems that I still need some more sources to keep the heat in the core up. Friction for instance.

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Quid est ergo tempus.
Augustinus

I don't think the radiogenic material is necessarily required--and that calculation seems to be at an upper limit.

The heat may be left from formation, and a lot may be released as the outer core solidifies into the inner core.

I think you mean 10^17 kg (where did the "-" come from?)I think "TW" = "terawatts", which is 10^12 watts, so if your quote is correct, you and your source differ by 1.4 vs 4.5.IIRC, it isn't.

Nereid said:
It was an attention checker :wink: You passed. Or a typo 8-[

Right I made the calcs using my own links to -hopefully correct- sources.

Abundance of 40K One in 10,000 (10 mils)

Mass of the core I see now that I missed the inner core (1.162 x10^23) or the total mass increases by 6,5% making the heat production estimation 1,5 TW

40K data.

I rest my case: 1,5 TW, not 4,4 TW

But there is a lot more to study about the abundance of Potassium.

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Quid est ergo tempus.
Augustinus

As you say, more to study about the abundance of K.

Also, you might consider +/- numbers; for example, the relative abundance of K-40 certainly isn't exactly 1 part in 10,000, it's maybe 9,234 to 10,123 (I made these numbers up).

That would give you a better handle on (for example, also made up numbers) 1.1 to 2.1 vs 3.9 to 4.6 (cf 1.5 vs 4.5)

Yes, thanks we could figur something with min and max values.

Anyway, since the thread seems no able to stir up more elements, I think there is one more thing to show. I mentioned in an earlier post:

Let me give one example of that evidence. After working our way trough much recent geologic work we reconstructed the North Pole during MIS-3, roughly 55-30,000 years ago:

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Augustinus

Allow me to dig up this old thread.

I've done a bit more study on the Venus literature and found a lot of supporting evidence.

Examples:

The volcanic activity of Venus was very high at the beginning of the recognisable eras after resurfacing and decreased two orders of magnitude in the later periods.

The crust of Venus was rather thin in the older periods but is now assumed to be much thicker as the Earth crust.

The magnetic field of Venus is not measurable

The local gravity differentiation shows a very high corrolation with topography.

These facts combined make me think that Venus interior has cooled considerably, to an extent that heat convection is no longer happening. All of this would fit with the spinning-generates-precession-creates-friction-generates-heat idea.

Anyway the very first draft of the paper is nearing completion and I could certainly use some objective constructive (pre)peer reviewers.

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Quid est ergo tempus.
Augustinus