Venus' mysteries, another view.

[Andre]

I hope I'm not too bold to start a thread straight away as a newby John Doe and no astronomer at all, but I have been focussing on planet Venus for a while now. I have no questions -at the moment at least- but maybe answers instead. I happen to stumble upon a (psysically possible?) mechanism that may explain Venus enigmatic features, all them them.(temperature, atmosphere, rotation, resurfacing, surface features)

After studying:

http://astro.oal.ul.pt/~acorreia/cvpubs/venus1.pdf
http://astro.oal.ul.pt/~acorreia/cvpubs/venus2.pdf

and

http://spaceflightnow.com/news/n0103/13venus/
http://volcano.und.nodak.edu/vwdocs...us/unusual.html

and

http://spacelink.nasa.gov/NASA.Proje...us.Discoveries

But this story is quite a bit different from all those "solutions", I should say. So care to listen to a crackpot?

[Conor_M]

Say your peace, people will listen, crack pot or not

Whether or not they will believe is another story, but I'm sure most people here are open minded.

[Nereid]

I've read some of your material Andre, in another forum, and I certainly wouldn't call you 'a crackpot'!

[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.

Venus has four unusual main features:

1. Its slow retrogade spinning.
2. A dense CO2 atmosphere of 90+ bar.
3. Extreme high temperatures of 450-460 degrees C.
4. Abnormal surface features that suggest a complete resurfacing 500My ago

The features are explained in various ways but none is universal and some contradict each other. However there is a single possible explanation for all of them.

We start assuming that Venus was a normal planet just like Earth. There are many differences however, for instance, Venus seems not to have a liquid outer core today. It is unknown if it has had one before but using the analogy with Earth we assume that it did. So lets first look at a hypothetical normal planet with mostly Earth-like features assuming Earth is the standard, not Venus.

The outer core of such a standard planet can be fluid mass, due to the high temperature. However, the inner core of a planet is solid again due to the immense pressure it is subjected to, in spite of the temperatures. In the core is a equilibrium between those two opposing tendencies.

It is spinning around the sun and spinning around its axis in a much similar way with same order of magnitude parameters. By spinning the planet behaves as a gyroscope or spinning top and can be subject to changes in spin axis direction by precession.

Just like Earth this juvenile planet Venus also has precession of the equinoxes due to a certain obliquity and the sun and (perhaps a possible moon) having a differential gravity pull on the equatorial bulge.
see also

http://cse.ssl.berkeley.edu/lessons/...h_precess.html

Other planets are also in precession, there is no moon required for that, just gravity, generally

Now we assume the planet to be a single unit, a single gyroscope with a single mechanical reaction. But it isn’t. The mantle and the solid inner core could be pretty much independent gyroscopes, with different characteristix, tied together by a fluid outer core.

I think we can assume from the mechanism that the sun-moon gravity force that generates the precession, is basically working on the equatorial bulge and hence on the lithosphere/mantle.

Now does the precession also work on the solid inner core? It may have an equatorial bulge. However, due to non-linear relationships, the precession logic of the inner core must differ from the mantle-crust precession. (see also Correia et al part I, 3.2) in the opening post.

Hence the inner core has a tendency to change its spin axis in relation to the mantle crust due to dissimilar precession tendencies.

Note that the precession itself actually rotates spinning axis and hence it is changing the vector direction of the angular momentum. External forces, like gravity between celestial bodies transfer momentum this way.

The fluid outer core couples the motions of both solid systems. To keep spin axis aligned, the fluid outer core has to transmit these precession movements from mantle to the solid inner core somehow, like a torque converter in a transmission gear of a car. It contains some natural mechanic and perhaps magnetic stabilising properties to correct for that drifting motion, as we see no problems on Earth today, but its stabilising capacity is limited and can only physically control a limited angular momentum.

The size of the solid inner core is a function of amount of heat and pressure. The high temperature leads to liquefying and the high pressure leads to solidifying. But as the planet is cooling the amount of heat is decreasing and hence the solid inner core is expanding while the outer core is shrinking. The turning momentum of the inner core is of a tremendous value and the inner core grows, it’s increasing its angular momentum rapidly, to the fifth power of the radius, if I'm right

As the core grows its angular momentum increases beyond stabilization, eventually its precession drift will break alignment of the spinning axis. This causes heavy turbulence in the fluid outer core affecting the motion of the mantle and the inner core and it also generates drag and heat. The heat may have partially liquefied the solid inner core, decreasing it’s angular momentum and reversing the whole process back to stability. When the precesssion cycle is completed, realigment and stabilisation can occur again. However cooling continued and the inner core precession break out would occur again and this process may repeat over and over again until the spinning stops eventually.

Note that the growing misalignment of the spin axis causes the vector sum of the angular momentums of the mantle and the core to decrease, whilst angular momentum is transferred via external gravity forces to the infering celetial body during the precession. The actual transfer of momentum becomes visible only after the realignment, when a precession cycle is complete. There is no momentum loss, just momentum transfer over billions of years

The generated heat will be transmitted throughtout the whole planet, facilitated by the increased heat transport capability of the turbulent fluid outer core, causing the planet to melt partially or as a whole. Due to the heat convection the planets surface would be renewed by convection of material. As the heat would exceed general melting temperature it would also enough to cause limestone to decompose into calcium oxide and carbon dioxide that happens around 1100 degrees celsius. The carbon dioxide would escape from the lithosphere via the characteristic dome volcanoes (pancakes) to form a dense atmosphere. After the precession induced rotation stop, a very hot planet would remain with a dense carbon dioxide atmosphere. It would cool only very slowly as the carbon dioxide works as an isolation blanket and also retains solar heat due to greenhouse effect.

Due to interaction of the dense atmosphere with the sun stable equilibrium will emerge eventually.
Correia and Laskar (A Correia and J Laskar 2001 Nature 411 767) found that the rotation can only end in four possible spin states. Such planets can have either retrograde or 'prograde' rotation and its rotation axis may or may not have flipped during the turbulent precession braking event.

Venus has retrograde rotation now, but a flip of its rotation axis may not be likely. Most initial conditions will drive the spin of Venus towards its present state. The resulting slow spin sets a scenario for the retrograde stable motion purely from atmospheric and internal phenomena

In the mean time we have addressed all enigmatic features,

1: the rotation stop as a combination of the big precession brake and the Correia atmospheric drag mechanism
2: the resurfacing due to a tremendous heat generated by the hot brake, partially melting the planet.
3: the dense carbon dioxide atmosphere as all the carbon was forced out the lithosphere by chemical processes under the extreme heat.
4: the heat itself as residual from the disaster that seems to have ended 500 million years ago.

The finish is here, anybody followed me?

edit for fixin link

[Andre]

Hi Nereid, thanks, you beat me by a minute I see.

[milli360]

There is no momentum loss, just momentum transfer over billions of years

Are you saying that one layer (say, the mantle) is spinning one direction and the other layer (say, the inner core) is spinning another direction during one era, and they line up (and therefore cancel) during another (preceding or succeeding) era?

[Andre]

Sort of, Milli

I propose that both spin axes of both part-gyroscopes may have lost alignment due to different precession tendency and the momentum of the core too big to follow the mantle precession.

but also the precession is causing the spin axes following a cone and eventually the spin axes will realign when the conical movement is completed. For Venus this is not very important since the basic message is that spinning energy was converted to heat in a very rapid way, calling it the big brake hypothesis.

But for Earth it's a different story.

[Eye-Zee]

I have trouble understanding how/why the precession of inner core and mantle can get so misaligned when they start out from the same spinning/differentiating planetessimal (and why, if it happened on Venus, it has not happened on Earth). Venus' inclination of it's equator to its orbit is 0.5 degrees. Wouldn't it have to be substantially higher for the core and mantle to be so misaligned that they "slow each other down." Plus, wouldn't conservation of angluar momentum for the planet as a whole argue for the thing to end up spinning plretty much as it started? This ain't my strong suit, so I don't know if I'm missing something fundamental.

[milli360]

For Venus this is not very important since the basic message is that spinning energy was converted to heat in a very rapid way, calling it the big brake hypothesis.

So, at the present time, the angular momentum of both is near zero, but before they were larger in magnitude, but nearly opposite?

[JohnOwens]

I think I see one moderate problem here:

The fluid outer core couples the motions of both solid systems. To keep spin axis aligned, the fluid outer core has to transmit these precession movements from mantle to the solid inner core somehow, like a torque converter in a transmission gear of a car. It contains some natural mechanic and perhaps magnetic stabilising properties to correct for that drifting motion, as we see no problems on Earth today, but its stabilising capacity is limited and can only physically control a limited angular momentum.

The size of the solid inner core is a function of amount of heat and pressure. The high temperature leads to liquefying and the high pressure leads to solidifying. But as the planet is cooling the amount of heat is decreasing and hence the solid inner core is expanding while the outer core is shrinking. The turning momentum of the inner core is of a tremendous value and the inner core grows, it’s increasing its angular momentum rapidly, to the fifth power of the radius, if I'm right.

As the inner core cooled and gained (relatively) solid material from the outer core, wouldn't it also pick up some of the angular momentum from it? And presumably, this angular momentum would be somewhere between that of the mantle and that of the inner core. Thus, it seems to me it certainly wouldn't increase the angular momentum as the fifth power of the radius, and might even actually decrease it (especially if the mantle is spinning in the completely opposite direction from the inner core).

[Andre]

why the precession of inner core and mantle can get so misaligned when they start out from the same spinning/differentiating planetessimal

Because the precession is a function of differential gravity, which is a function of the geoid shape of the planet. Whilst this shape is not the same as the shape of the inner core and the relationships is not linear, the inner core will allways have a different precession tendency as the mantle. But I did invent that. Check Correia, he says the same, only he assumes that the fluid inner core accounts for this tendency and as a consequence also induces a little drag, slowing down the spinning.

it has not happened on Earth

Stand by to be surprised. Anyway we have different parameters on Earth. A precession cycle of 26 Ky is orders of magnitudes faster than we may have expected from Venus without a decent moon.

Plus, wouldn't conservation of angluar momentum for the planet as a whole argue for the thing to end up spinning plretty much as it started?

You may have noticed that I tried to preserve angular momentum very carefully. But no matter which mechanism you would propose for a spinning stop it always have to deal with with that. So if you can't accept it from my proposal, then the same goes for Correia. But we are talking about preservation of momentum of the total system (galaxy wide if you so desire) So Venus distance to the sun has to increase a little to account for the conservation of momentum.

More later.

[Andre]

Venus' inclination of it's equator to its orbit is 0.5 degrees. Wouldn't it have to be substantially higher for the core and mantle to be so misaligned that they "slow each other down

Yes that's the current end state. But if we assume a more Earth like behavior in the past with a "normal" prograde spinning, at some point the spinning stopped completely and after that Correia's mechanism took over to induce the retrogade spinning. but the spin axis of both spinning would not necesarely have been the same So the previous prograde spinning could have had any inclination.

As the inner core cooled and gained (relatively) solid material from the outer core, wouldn't it also pick up some of the angular momentum from it? And presumably, this angular momentum would be somewhere between that of the mantle and that of the inner core. Thus, it seems to me it certainly wouldn't increase the angular momentum as the fifth power of the radius,

Just a minute, let's check the math. Angular momentum (L) is moment of inertia (I) times angular velocity (W) or

L = I x W (vector)

The moment of inertia of a sphere is 2/5 times mass (M) times radius (r)square or:

I = 2/5 * M * r^2

The mass of a sphere is volume times density (p) or

M = 4/3 * pi * r^3 * p

Now merge everything and we get:

L = (8/15) * pi * p * W * r^5

So if the solid inner core picks up mass from the fluid outer core a transfer of momentum also happens and to the fifth power of the radius. Consequentely the fluid outer core looses momentum and hence the inertia to correct the wandering precession difference.

[TriangleMan]

Um, I not an expert on planetary geology so could someone speculate on how this model would affect the magnetic field of a planet? If the inner core was spinning one way and the outer core a different way could that be detected in the magnetic field?

[milli360]

So if the solid inner core picks up mass from the fluid outer core a transfer of momentum also happens and to the fifth power of the radius. Consequentely the fluid outer core looses momentum and hence the inertia to correct the wandering precession difference.

The problem quickly becomes very complex after that though. You seem to be ignoring the density changes as material freezes out to the inner core, and the friction between the inner and outer core--which could prevent a large difference in rotational speed. I doubt that a planet could have a rotation like the Earth, and an inner core rotating similarly in the opposite direction. The viscosities are immense.

[Andre]

seem to be ignoring the density changes as material freezes out to the inner core,

Why? did I suggest that? As a matter of fact as the density increases while the matter is solidifying this also means that the effective radius is decreasing. Conservation of momentum requires an increase of angular velocity. And guess what, Earth inner core is spinner faster. although you can always find another hypothesis to explain that.

I doubt that a planet could have a rotation like the Earth, and an inner core rotating similarly in the opposite direction.

I merely said that both spin axes were out of alignment. We may be talking about a few degrees. One of the sinning bodies may be leading or lagging slightly. Most certainly not 180 degrees.

The viscosities are immense.

Well from what I know, the estimates for the viscosity value of the outer core vary about 12 orders of magnitude. It may be more fluid than water.

[Andre]

If the inner core was spinning one way and the outer core a different way could that be detected in the magnetic field

If the current dynamo models for magnetic field are accurate than there should be a violent reaction. Most likely the field strenght would collapse due to the flow turbulence. Venus however has no measurable magnetic field suggesting that it's interior is at rest presently or perhaps that mantle lithosphere temperatures have exceeding demagnetizing temperatures.

[Andre]

Just a few more remarks. The narration may suggest that such a big brake happened overnight, as soon as the mantle and inner core counter-rotated. I think the process could easily have taken several hundred million years using perhaps hundreds of precession cycles, each time the spinning was reduced by a very little amount. The heat would also take several hundred thousend years before it reached the surface. It may have taken a very long time before the planet died.

Also about the conservation of momentum. When the braking action actually takes place, the spinning is reduced, this appears to be a loss in angular momentum, but the transfer of momentum happens continuously when the solar gravity acts upon the equatorial bulge, when the momentum vectors of the mantle and core start to diverge, the indivual value of the momentums is not affected, but the vector sum is decreasing. Only when both realign after loosing spinning energy, the combined momentum values are less. If anybody is able to follow my thoughts.

The question is, of course if it is also happening to Earth.

[Eye-Zee]

it has not happened on Earth

Stand by to be surprised.

Standing by.

The viscosities are immense.

Well from what I know, the estimates for the viscosity value of the outer core vary about 12 orders of magnitude. It may be more fluid than water.

If I read correctly, the research presented in that link indicate the low end of viscosisty is more likely in the Earth: "...roughly 10 times that of typical liquid metals at ambient pressure. The authors suggest this estimate supports the approximation commonly made in magnetohydrodynamic models that the outer core is an inviscid fluid undergoing small-scale circulation and turbulent convection, rather than large-scale global circulation."

I understand that other estimates range up to 12 orders of magnitude, but the report you cite implies exactly the opposite of "more fluid than water". I find it counterintuitive to think of liquid iron at outer core pressure as being less viscous than water, but would have to read up on the rationale and modeling behind the various estimates to make an informed judgement.

Another question - unless you posit that Venus was spinning retograde to begin with, how does this mechanism get the current state to be retrograde rotation instead of tidelocked with the sun. I'm certainly showing my colors as a non-dynamicist here, but again, this seems counterintuitive.

[Andre]

I find it counterintuitive to think of liquid iron at outer core pressure as being less viscous than water,

Well, I posted that link to quickly perhaps. But I knew that I did not invent that either:

that strange processes may be going on at the boundary between the mantle, made up of viscous rock that extends 1,800 miles below the crust, and the outer core, which is thought to be liquid iron with the consistency of water.

I know, in the business of persecuting paradigms, it’s not wise to state anything without robust substantiation

But what have we here? “Counterintuitive”? It’s natural to appeal to intuition or common sense (the prejudice acquired by age eighteen - Albert Einstein) but you, Astronomers, are very used to gigantic phenomenons, super novas, big bangs, black holes, nothing is too weird, yet the moment that we deliberate terrestrial planets with some unusual gigantic phenonenons, “intuition” kicks in. Personally I think physical laws defeat intuition. Precession for instance is not something you would have thought of intuitively. Anyway.

unless you posit that Venus was spinning retograde to begin with, how does this mechanism get the current state to be retrograde rotation instead of tidelocked with the sun

Fortunately Correia et al was so kind to have a nice explanation for that.

Was Venus born retrograde or not?

The first success was that of Gold and Soter (1969), who proposed that the present spin was near a steady state resulting from a balance between a gravitational tidal dissipation which drives the planet toward synchronous rotation and thermally driven atmospheric tides which drive it away. However, tidal effects alone could not explain how to prevent Venus’ spin axis from rolling over to a prograde orientation (Dobrovolskis, 1978).

Goldreich and Peale (1970) proposed that friction at a core–mantle boundary should drive the spin pole to a fully dampened obliquity state which ends with retrograde rotation. The only requirement for this is that the planet’s orientation is already retrograde when the core–mantle friction becomes important. Taking into account the dissipation of tides (both gravitational and thermal) and core–mantle friction, Lago and Cazenave (1979), Dobrovolskis (1980), Shen and Zhang (1989), McCue and Dormand (1993), and Yoder (1995) proposed different scenarios where the venusian axis was tilted down during its past evolution, but this still required high values of the initial obliquity.

Laskar and Robutel (1993) discovered that, for all terrestrial planets, there is a wide set of possible spin states for which the obliquity undergoes strong chaotic variations with large amplitudes over a few million years. This is due to some resonance overlap between the precession frequency and combinations of secular frequencies of the planetary orbits. The future passage of the Earth through the chaotic zone was analyzed as well (Ne´ron de Surgy and Laskar, 1997), and it was shown that our planet’s spin has a high probability to reach obliquities as high as 90° within a few billion years. Because the chaotic zone of Venus (Fig. 1) is comparable to that of the Earth, Laskar and Robutel (1993) suggested that planetary perturbations could have played an essential part in the history of the venusian spin.

If Venus was born with an obliquity lower than 90° and initial rotation period faster than 5 days, it surely wandered for a while in the chaotic zone. Indeed, Ne´ron de Surgy (1996) and Yoder (1997) showed that dissipative effects combined with planetary perturbations could tilt the spin axis to 180° starting with any initial obliquity. Finally, Correia and Laskar (2001) confirmed this last result and found that the present spin state of Venus is the most probable for almost any initial condition. They also showed that it is possible to evolve to the present configuration through a different scenario where retrograde rotation is developed while the obliquity goes toward zero (suggested by Kundt, 1977). Although the outcomes of the dissipative effects are supposed to be well understood, their precise mechanisms are poorly known, as is the initial spin state of Venus.

Long-term evolution of the spin of Venus
Alexandre C.M. Correia,a,b,* Jacques Laskar,b and Olivier Ne´ron de Surgyb
Received 7 January 2002; revised 30 December 2002
Elsevier Academic press

I concur absolutely and have nothing to add to that.

Standing by

Well, perhaps stick with Venus first but I discovered the Venus story when I toyed with a little pet idea about I had discovered for Earth. But the acceptance of such a thing on Earth would be orders of magnitude lower than on our twin planet. Anyway, let me know if you want to peek ahead.

[Eye-Zee]

I find it counterintuitive to think of liquid iron at outer core pressure as being less viscous than water,

Well, I posted that link to quickly perhaps. But I knew that I did not invent that either:

After finding a few more sources I have no basis to argue the point.

But what have we here? “Counterintuitive”?

With the amount of time I'd spent on the subject so far, that's what I had. Certainly intuition can be misleading. I make no claim that intuition is sufficient, and appreciate the extra references.

...but you, Astronomers,

I am not an astronomer. Neither am I a geodynamicist. If my intuition errs, it is not because I think in terms of stellar phenomena.

Precession for instance is not something you would have thought of intuitively.

... unless you play with tops.

Fortunately Correia et al was so kind to have a nice explanation for that.

Interesting. Thank you for the ref.

[JohnOwens]

As the inner core cooled and gained (relatively) solid material from the outer core, wouldn't it also pick up some of the angular momentum from it? And presumably, this angular momentum would be somewhere between that of the mantle and that of the inner core. Thus, it seems to me it certainly wouldn't increase the angular momentum as the fifth power of the radius,

Just a minute, let's check the math.
(Derivation snipped)
L = (8/15) * pi * p * W * r^5

So if the solid inner core picks up mass from the fluid outer core a transfer of momentum also happens and to the fifth power of the radius. Consequentely the fluid outer core looses momentum and hence the inertia to correct the wandering precession difference.

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.

[Andre]

or airplane brake, which I know better

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.

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).

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.

[Andre]

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:

Dr. Kasting's "wet greenhouse" theory suggests that this enormous
primordial atmosphere was reduced to a small part of its original mass by
ocean-planet interactions. This would have left Venus's atmosphere about
the same size of Earth's. The thin Earth-like atmosphere then lasted
several hundred million years.

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.

[Brady Yoon]

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

[Andre]

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.

[Andre]

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

2.2.4. The initial spin rate of Venus

The initial spin rate of Venus is not know as very few constraints can be derived from the present planetary formation models. A small number of large impacts at the end of the the formation process of a planet will not average, and they can change a planets's spin rate or direction (Dones and Tremaine, 1993), on the other hand, the empirical relation w1=Km^(4/5)R^-2 given by MacDonald (1964) leads to Pi=13.5 h for Venus. Overall, the only strong constraint on the initial spin rate of Venus seems to be its present observed slow rotation. In figs. 1 and 3, we chose for the initial rotation period Pi=3 days...

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.

[Andre]

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.

[captain swoop]

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.

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

spell edit

[Andre]

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

[Eye-Zee]

Getting quiet here :o . 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.
...
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.

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