Venus' mysteries, another view.

Andre · #1 (**permalink**) 14-April-2004, 05:28 PM

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 · #2 (**permalink**) 14-April-2004, 06:54 PM

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 · #3 (**permalink**) 14-April-2004, 07:17 PM

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

Andre · #4 (**permalink**) 14-April-2004, 07:18 PM

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.

Quote:

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 · #5 (**permalink**) 14-April-2004, 07:53 PM

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

milli360 · #6 (**permalink**) 14-April-2004, 08:13 PM

Quote:

Originally Posted by Andre

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 · #7 (**permalink**) 14-April-2004, 08:26 PM

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 · #8 (**permalink**) 14-April-2004, 08:38 PM

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 · #9 (**permalink**) 14-April-2004, 08:42 PM

Quote:

Originally Posted by Andre

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 · #10 (**permalink**) 15-April-2004, 05:31 AM

I think I see one moderate problem here:

Quote:

Originally Posted by Andre

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 · #11 (**permalink**) 15-April-2004, 06:58 AM

Quote:

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.

Quote:

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.

Quote:

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 · #12 (**permalink**) 15-April-2004, 10:45 AM

Quote:

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.

Quote:

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 · #13 (**permalink**) 15-April-2004, 11:08 AM

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 · #14 (**permalink**) 15-April-2004, 11:16 AM

Quote:

Originally Posted by Andre

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 · #15 (**permalink**) 15-April-2004, 01:14 PM

Quote:

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.

Quote:

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.

Quote:

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 · #16 (**permalink**) 15-April-2004, 01:28 PM

Quote:

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 · #17 (**permalink**) 15-April-2004, 01:48 PM

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 · #18 (**permalink**) 15-April-2004, 02:20 PM

Quote:

Originally Posted by Andre

Quote:

it has not happened on Earth

Stand by to be surprised.

Standing by.

Quote:

Originally Posted by Andre

Quote:

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 · #19 (**permalink**) 15-April-2004, 06:26 PM

Quote:

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:

Quote:

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.

Quote:

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.

Quote:

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 c