View Full Version : Solving the mystery of Venus
I got the planet Venus solved (I think). Exiting analysis. Anybody interested??
mathman
Jun12-03, 08:04 PM
Could you be a little more precise as to what you mean by "solving Venus"?
Yeah... What's the problem with Venus ?!
Brad_Ad23
Jun14-03, 04:34 PM
The only odd things I know about venus is that it orbits the opposite direction as the rest of the planets, its day is longer than its year, and it has a runaway greenhouse effect. Do any of those cover the "mystery of venus" that you solved?
Originally posted by Brad_Ad23
The only odd things I know about venus is that it orbits the
opposite direction as the rest of the planets,
Oh... I forgot about that ! [:(]
Well, my guess would be that it can only be caused
by an extrasolar body that enitially formed into Venus.
Anyway, what's your solution ?
Live long and prosper.
Originally posted by Brad_Ad23
The only odd things I know about venus is that it orbits the opposite direction as the rest of the planets,
Did you mean it rotates in the opposite direction? Venus orbits in the same direction as the other planets, but it rotates the other way.
What specifically have you "solved" (possibly), Andre?
ObsessiveMathsFreak
Jul3-03, 09:52 PM
But Uranus rotates at alomost 90 degress to the solar plane.
Oops I was preocuppied the last couple of days. I think I forgot about this thread and started another one here:
http://www.physicsforums.com/showthread.php?s=&threadid=3354
I'll repeat my posts:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Venus
The atmosphere consists mainly of carbon dioxide (the same gas that produces fizzy sodas), droplets of sulfuric acid, and virtually no water vapor - not a great place for people or plants! In addition, the thick atmosphere allows the Sun's heat in but does not allow it to escape, resulting in surface temperatures over 450 °C, hotter than the surface of the planet Mercury, which is closest to the Sun. The high density of the atmosphere results in a surface pressure 90 times that of Earth, which is why probes that have landed on Venus have only survived several hours before being crushed by the incredible pressure. In the upper layers, the clouds move faster than hurricane- force winds on Earth.
Venus sluggishly rotates on its axis once every 243 Earth days, while it orbits the Sun every 225 days - its day is longer than its year! Besides that, Venus rotates retrograde, or "backwards," spinning in the opposite direction of its orbit around the Sun. From its surface, the Sun would seem to rise in the west and set in the east.
Earth and Venus are similar in density and chemical compositions, and both have relatively young surfaces, with Venus appearing to have been completely resurfaced 300 to 500 million years ago.
The surface of Venus is covered by about 20 percent lowland plains, 70 percent rolling uplands, and 10 percent highlands. Volcanism, impacts, and deformation of the crust have shaped the surface.
Suppose that Venus has been like the other inner planets, the Earth and Mars, rotating likewise, in the same direction of the orbit, with much similar features.
According to the conventional ideas, the cores of the planets generate heat due to compression, possible nuclear decay processes, Not much difference between Venus, Earth and Mars yet.
Venus was probably rotating normally a few billion years ago, likely the spin axis also being sa bit tilted like the Earth. Also, it has an equatorial bulge and with those properties, also a precession movement, just like Earth, the Precession of the Equinoxes. This precession is supposed to be caused by differential gravity pull of the sun and moon on the closest and farther part of the equatorial bulge. It caused the spin axis of the planet to slowly make a cone like movement
Again the planets are still much the same. Perhaps two things slightly different for Venus, Again, it hass less mass than the Earth and because of that is has compressed less, therefore it may have a slightly bigger core With less compression and perhaps less heavy mass from radiactive elements the core did not heat up that much and Venus may have cooled faster than the Earth.
The core of the earth consist of a liquid outer core and a solid inner core. It is solid despite the high temperature due to the immense pressure it is subjected to. In the core there is a equilibrium between two opposing tendencies, the high temperature tries to liquefy the core and the high pressure tries to solidify the core. Where pressure is higher(inner core) the core is solid and where temperature is higher in relation to the pressure (outer core) it is liquid. But as the earth cools the temperature decreases and hence the solid inner core expands at the cost of the outer core. Since cooling is much faster for the smaller and lighter Venus it may be that the same process took place million of years ago.
These are the basic elements we need. So, what made Venus to the counter rotating Dante’s inferno that it is now?
So anybody like a shot at it?
Jonathan
Aug3-03, 06:09 AM
Maybe the liquid outer core of Venus has become solid, leading to a callapse of the magnetic field and all sorts of directly related enviromental cataclysims. Though I don't think that would explain why it rotates so slowly. Would a solidification of the liquid outer core affect volcanism? It seems like it would, and though I'm not sure I think Venus' volcanism is dead or dormant, maybe thereby proving it's inner/outer cores have solidified into one. But what happened to all it's angular momentum? Did something hit it in the formative years like Uranus, (instead of knocking it over it almost nullifying it's spin)?
How Venus died
We digressed to Venus when discussing palaeo global warming in another thread. Ivan Seeking brought up this old thread but there should be still another. Anyway happy to post once more how Venus died.
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://www.copernican-series.com/precession.html
http://cse.ssl.berkeley.edu/lessons/indiv/beth/beth_precess.html
on precession
Other planets are also in precession, there is no moon required for that, just gravity, generally here is the math behind the idea:
http://scienceworld.wolfram.com/physics/Obliquity-InducedPrecession.html
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):
http://astro.oal.ul.pt/~acorreia/cvpubs/venus1.pdf
http://astro.oal.ul.pt/~acorreia/cvpubs/venus2.pdf
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.
Very interesting Andre.
Before we look at your ideas further, might I suggest that you summarise
a) what 'thermal atmospheric tides' are
b) the evidence for a liquid Venusian core, its estimated size and mass
c) the key parameters (and factors) which Correia et al state are 'poorly known' or 'poorly understood'
d) importance of these parameters and factors in your proposed resolution of the Venus problem.
Okay, lets give it a try.
'thermal atmospheric tides'
I mentioned "atmospheric drag" but that should be the same. The analogy is with Earth and moon interaction. The Earth has to fight it's way spinning trough the tides of the ocean waters. It produces drag and the forces that are associated with this cause spinning to slow down and an exchange of angular momentum with the moon. However this drag on Earth is actually confined to a few meters of tide whereas the atmosphere of Venus (92 Hectopascal) is rougly equivalent to a continouis water ocean of 900 meters deep.
the evidence for a liquid Venusian core, its estimated size and mass
None whatsoever. What is the evidence of an Earth liquid core? It's just a (very sophiscated) assumption based sound physical evidence.
But we assume the parallel development of Earth and Venus within the same order of magnitude for about all parameters. So it follows that there should have been a similar composition for both planets.
There are assumptions about the Venusian core, based on nowadays evidence to be about the same as Earth. However what is fluid and what is solid is not known at present. There are suggestions of a partial liquid mantle though.
the key parameters (and factors) which Correia et al state are 'poorly known' or 'poorly understood'
Did they? Good.
The essential problem is the initial spinning rate of Venus. Correias model cannot handle anything less than 3,5 days. (it's in the links-chapter 2 ) however a parallel development with Earth would suggest an initial spinning rate of the protoplanet Venus of some 13,5 hours. This is a tremendous difference in angular momentum and energy.
Moreobver the "wet greenhouse runaway model" would conflict with Correia. That model assumes a "normal" earthlike atmosphere of the protoplanet for several billion years, whereas Correia needs the current 92 hectopascal atmospheric pressure from the onset to explain the loss of turning rate.
importance of these parameters and factors in your proposed resolution of the Venus problem.
I'm afraid I dont understand the question completely. Apart from the deficiency in rotation rate that should be a major problem for Correia, but this is insignificant for the the big brake model.
Note also that Correia et al address the problem of differential mantle-core precession (part I, chapter 3.2 "Core Mantle Friction" page 8) but fails to work it out. He was so close.
Loren Booda
Feb29-04, 06:43 PM
My SWAG: Venus might have a highly radioactive core. The resultant heat could explain the maintenance of resurfacing up to 500My ago, extremely high temperatures today, outgassing of CO2 under pressure, and substantial liquid core that has yet to succumb completely planetary spin to the influence of the Sun's tidal forces.
Originally posted by Loren Booda
My SWAG: Venus might have a highly radioactive core. The resultant heat could explain the maintenance of resurfacing up to 500My ago, extremely high temperatures today, outgassing of CO2 under pressure, and substantial liquid core that has yet to succumb completely planetary spin to the influence of the Sun's tidal forces. Just to recap, my reading of Correia et al is:
- today's rotation rate of Venus is stable, and pretty much assured, irrespective of initial conditions (with caveats, of course)
- the only real question is, how did it arrive at that rate?
How much radioactivity do you think the core might have, Loren? What concentrations, over 'Earth+Moon' abundances, might there be for the key species (I guess, U238 and Th232; K40 wouldn't concentrate in the core, or no?)
Loren Booda
Mar1-04, 12:03 AM
Of course, the heavier radioactive species would tend to collect toward the Venusian core. Their relative abundances would be significantly greater than in the Earth-Moon system since the proto-Moon's contribution to radioactivity at time of impact was negligible (no volcanic activity there at present), and since the more interior planets shared a greater proportion of the higher atomic weight atoms. One must also acknowledge a slower cooling rate on Venus due to greater solar luminosity over the Venusian surface, the CO2 greenhouse effect, and the solar tidal effects changing rotational and gravitational into thermal energy, to account for the thermodynamic differences we observe between those two planets.
Well the nuclear core reactor is an idea of J. Marvin Herndon (http://www.nuclearplanet.com). Interesting enough he did some modeling with different size "reactors" and he concluded that the running time of the reactor was about inversely proportional to its size varying between some 3-8 billion years. Can't find it back exactly. The numbers should give rough idea. So if he is right and Loren is right about much more heavy elements in the core of Venus, than it is perfectly logical that Venus reactor burned out much more earlier than Earths reactor, explaining why Venus started this braking movement. Why? as soon as the reactor stops the planet cools, causing the core to solidifying and to grown and thus increasing its angular momentum up until a point that precession anomalies could not be corrected anymore. [:D]
Unfortunately the nuclear core has met a tremendous oppostion as Andrew Alden (http://geology.about.com/library/weekly/aa072102a.htm) observes and having some vere elementary basic knowledge about nuclear reactors I'm afraid, I have to admit that he has a case. [:(]
It's hard not accepting an hypothesis that supports your own hypothesis perfectly.
Thermal atmospheric tides (Correia et al, per Andre's earlier post):
"The differential absorption of solar heat by the planet’s atmosphere gives rise to local variations of temperature and consequently to pressure gradients. The mass of the atmosphere is then permanently redistributed, adjusting for an equilibrium position. More precisely, the particles of the atmosphere move from the high-temperature zone (at the subsolar point) to the low-temperature areas. Indeed, observations on Earth show that the pressure redistribution is essentially a superposition of two pressure waves (see Chapman and Lindzen, 1970): a daily (or diurnal) tide of small amplitude (in which the pressure is minimal at the subsolar point and maximal at the antipode) and a strong half-daily (semidiurnal) tide (in which the pressure is minimal at the subsolar point and at the antipode)."Nereid: c) the key parameters (and factors) which Correia et al state are 'poorly known' or 'poorly understood' "As the rheology of terrestrial planets is poorly known, the relation between the frequency and the time lag is often subject to some rough approximations."
"Unfortunately, our knowledge of the atmosphere response is not as complete as we wish it would be."
"Although lacking a magnetic field, Venus probably has a liquid outer core"
"The kinematic viscosity (\nu) is poorly known."
"The exact dependency of the dissipation time lags upon the tidal frequency is unknown."
"The precise evolution of Venus’ atmosphere is not known."
And there's likely more ...
UltraPi1
Mar7-04, 11:56 PM
http://www.ebtx.com/theory/global.htm
Good points, Nereid,
However uncertainties and unknowns are not as problematic as controversies:
See para 2.2.4. of Correia Part 2 (pag 5)
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
I guess, this should be the major problem for Correia. You need another basic understanding how the proto planets were build to accept such a deviation. Note that this difference in initial spinning state represents a factor 28 in spinning energy.
Notice, Ultrap1,
that Correia rejects much influence of impacts as your link suggests. I agree for several reasons.
First It's not a game of marbles, that react instanteneously. The tremendous inertia causes a signal delay of about 80-90 minutes. So an impact strong enough to stop the spinning on one side of the planet will not be noticed on the other side before one and a half hour. But the spinning continues on the second side, consequently, the planet(s) should disintegrete completely and the ultimate result was to be more likely another astroid belt.
Second, after the impact the planet would continue it's orbit with a total momentum equal to the sum of the previous momentums of both planets. If we could assume that protoplanets are formed from a particle cloud, it seems logical that its orbit would be circular. After a severe impact the change in momentum must result in an elliptical orbit. Venus'orbit is close to a perfect circle which would mean that it's previous orbit was elliptical where the impact would have corrected that orbit exactly to circular. Highly unlikely.
about the wind
I believe there is some minor wind at Venus surface. I seem to remember a story of a rock that the lander attemted to pick up but it slowly drifted out of view.
It is believed that the atmosphere of Venus is highly stable, preventing vertical circulation (convection). This is caused by real greenhouse effect. The IR radiation of the surface is heating the higher parts of the atmosphere, decreasing the vertical temperature gradient, this causes stability. If if there is little transport of heat, why are the poles of the planet and its backside from the sun about the same temperature as the equator that is full in the sun? My hypothesis gives a simple answer. The planet itself (hot brake) is its own main heat source.
Hi Andre,
I had planned to write a more extensive post, but reality injected a high-level interrupt (that's why my post looks rather unfinished).
Laskar, Correia, and the others seem to have done some quite nice work - not to mention that it's very interesting!
More later.
On another matter, there was a post of yours - which I can't find now! - that referenced another discussion, and "RFTG" (or something like this) - what do these letters stand for?
Maybe there are some anti-matter particles inside of venus.
Just a thought.
Nereid
The Rapid True Polar Wander (RTPW) is about some problems with the precession of the equinoxes (http://en.wikipedia.org/wiki/Precession) caused by differential gravity on the equatorial bulge.
Different precession of the inner core and mantle may have caused the spinning axis of both units to turn oblique. This created the big brake that stopped the spinning of Venus.
We have assumed that Earth and Venus are not that much different. So that same mechanism could also apply for Earth. It is my idea that something similar has happened albeit on a far smaller scale, thanks to the moon, which is accellerating the precession cycle to a staggering fast 26,000 years. This may have prevented the Earth from having the same fate as Venus, at least for the moment.
We think we can reconstruct those events rather precise. We may have figured out a possible secondary mechanical effect of oblique turning mantle-core spin axes that causes the mantle and core of the planet to wander off in relation to each other. We call that a Rapid True Polar Wander. But on Earth the effects are generally known as the "ice age" instead.
It's a long story though, Venus being the short version.
edit for splellin
Loren Booda
Mar8-04, 06:21 PM
Different precession of the inner core and mantle may have caused the spinning axis of both to turn oblique in relation to each other. This created the big brake that stopped the spinning of Venus. Ingenious, and seemingly possible. Is there supposed a discrete or continuous change in density at or over a given radius? Elsewise, might interior convection currents be the culprit?
Brad_Ad23
Mar8-04, 09:27 PM
I'll have to admit, this is one of the best ideas in Theory Development I've seen. I'm usually very skeptical about these, but you might be onto something. I'll see if I can't pick apart your idea some more later, but good idea.
Thanks
Loren B, Investigation progresses about the boundary layers (Core Mantle Boundary, inner-outer core boundart) in the interior of Earth but there is a lot of suppositions and perhaps controversies. Also very important seems to be the role of Earth (Venus) magnetism.
There is quite some literature about stability of the inner core. Poincaré being the pioneer on thermo-hydro dynamics. For me it's a big black box with the big question if a planets inner core can solidify and grow to such an extent that its precessing spinning momentum is too big the be corrected by the liquid outer core, acting as a torque converter of an automatic transmission gearbox.
Another issue is conservation of momentum. Any hypothesis dealing with the loss spin of Venus should deal with that. With gravitational interaction, transfer of momentum may take place with the sun, equivalent to the Earth-moon interaction and The vector sum of the individual momentums decreases during the process of diverging of the spin axes again caused by gravity interaction with the sun.
Furtermore, the increase in heat will melt the inner core partly agian, decreasing its momentum (or rather transfering momentum to the liquid part again). So the process may stop and the planet may recover. But during the cooling the inner core grows again and the process may repeat, time after time.
Note that a substantial greater heat in the past would allow for better explanations for several of Venus enigmatic surface features.
http://volcano.und.nodak.edu/vwdocs/planet_volcano/venus/unusual.html
http://spaceflightnow.com/news/n0103/13venus/
http://volcano.und.nodak.edu/vwdocs/planet_volcano/venus/lava_flow_features.html
Picking up the thread again and planning to bring it to a good end.
First working on the heat and the greenhouse theories. Basically there was the Runaway Greenhouse idea of Carl Sagan (http://www.aip.org/history/climate/Venus.htm) that has been under severe attack. Currently NASA propagates a wet greenhouse "theory" (http://spacelink.nasa.gov/NASA.Projects/Space.Science/Solar.System/Pioneer.Venus/Venus.Discoveries) that seems to fit better.
However, there is has been a major dispute about Venus albedo and the mere possiblity of a runaway Greenhouse effect. If too much sunlight is reflected due to the reflectivity of the clouds, not enough sunlight reaches the surface to create that greenhouse gas effect. The critical value seems to be around 78%.
Now the aparanted source of this dispute is...Ted Holden, of all crackpots.
http://www.skepticfiles.org/neocat/equalib.htm
The astronomers and others are citing Tomasko's article on pages
611 - 612 of THE BOOK (VENUS, Hunten, Colin, Donahue, Moroz, Univ. of
Arizona Press, 1983). This monstrosity is a size-equivalent to
War & Peace, GWTW, and the Bible, and costs $80 in North America. They
aren't making it on volume... One notes also that they clearly intend
that ordinary hoodlums (such as myself) should not have access to the
book; it turns out, this could cause some embarassment to the
astronomers.
It turns out, that there are two articles on thermal equilibrium, the
Tomasko article on pages 611 - 612, AND the article by F.W. Taylor
on page 658. It turns out that only by adopting the most myopic view which
it is possible to take can you get thermal equilibrium from this story, and
that is precisely what Tomasko does.
For thermal equilibrium to pertain, two numbers must match up; the
first is an emissions number which all parties involved agree reads
right at .76. The second number is a planetary albedo. Tomasko claims
(pp 611-612) "For the whole planet to be in equilibrium with absorbed
sunlight, the bolometric albedo would have to be .76..." Nobody
anywhere appears to disagree with that statement.
Now, the Pioneer Venus readings on albedo (Taylor's article, page 658)
was .80 plus/minus .02, and the calculations from Venera data (also
page 658) are .79, plus .02, minus .01. The closest you could get and
stay within error bounds is .78.
Now, you might ask, what's a lousy .02 amongst friends; doesn't sound
like much... This is one of those cases in which a little bit appears
to go a long way. Consider what Taylor claims would be required to
be believed if the .80 figure for albedo were to hold good (also page
658):
"Clearly, the Pioneer measurements of emission and reflection are not
consistent with eachother if radiative balance applies. A source
inside Venus equal in magnitude to 20% of the solar input (i.e.
accounting for the difference between A = 0.76 and 0.80 is very
unlikely since Venus is thought to have an Earth-like makeup which
would imply heat sources several orders of magnitude less than this.
Also, even if such sources were postulated, it is difficult to
construct a model in which these fairly large amounts of heat can be
transported from the core to the atmosphere via a rocky crust without
the later becoming sufficiently plastic to collapse the observed
surface relief. This could only be avoided if the transport were very
localized, i.e., via a relatively small number of giant volcanoes.
Although large, fresh-looking volcanoes do appear to exist on Venus
(see chapter 6), and the content of the atmosphere is consistent with
vigorous output from these, a simple comparison with terrestrial
volcanism shows that the volcanic activity on Venus would have to be on
an awesome scale to account for the missing 10^15 W or so of power."
If TH is right, then that would boost the big brake hypothesis considerably since that would require an tremendous internal heat source, which I can supply of course.
but I can't really use this as a thrustworthy reference, could I?
Anybody has any idea about the references of TH. What would the honest actual real albedo of Venus be? Anybody with access to the real data and the correct calculation?
Not sure why you're looking to close discussion of this Andre; as Brad said, it's one of the best threads in TD! Maybe the lack of responses is more due to rather too few PF members having sufficient background in planetary sciences. Did you try this on Bad Astronomy (http://www.badastronomy.com/phpBB/index.php?sid=dec3db8f181383f74564c0c5509a034a)?
What's your own take on the albedo - sources, calculations, error budgets, ...?
Why I made that post Nereid?
No hidden agenda really, or at least I don't like to see this thread sinking into the dusty archives. Moreover, the question is genuine and sincere, there are limits to google and the net.
This post (http://www.physicsforums.com/showthread.php?p=174442#post174442) may also help explaining. So I'm looking for a way ahead too.
Thanks for that link, I decided to be bold (http://www.badastronomy.com/phpBB/viewtopic.php?t=12818).
My own take on those subject? I don't like to speculate. Need facts. After a few hours of Googling, the albedo of Venus was anywhere between 68 and 80. So take your pick. This is also very interesting:
Abstract
Pioneer Venus observations of temperatures and radiative fluxes are examined in an attempt to understand the thermal balance of the lower atmosphere. If all observations are correct and the probe sites are typical of the planet, the second law of thermodynamics requires that the bulk of the lower atmosphere heating must come from a source other than direct sunlight or a thermally driven atmospheric circulation. Neither the so-called greenhouse models nor the mechanical heating models are consistent with this interpretation of the observations. One possible interpretation is that two out of the three probe sites are atypical of the planet. Additional lower atmosphere heat sources provide another possible interpretation. These include a planetary heat flux that is 250 times the earth's, a secular cooling of the atmosphere, and a chemically energetic rain carrying solar energy from the clouds to the surface. Other data make these interpretations seem unlikely, so measurement error remains a serious possibility.
Venus lower atmosphere heat balance
Authors: Ingersoll, A. P.; Pechmann, J. B.
Journal of Geophysical Research, vol. 85, Dec. 30, 1980, p. 8219-8222. December 1980
Of course the answer to that mystery is in this thread, what happened afterwards? Have the assumptions been adjusted like TH suggests? I really need a pro an insider to bring this to a good end.
Doctordick
May5-04, 05:20 PM
Andre has asked me to post a copy of a note I sent him last night. It was in response to a request from him that I read some varius threads to which he has posted. I believe the man with the brake analogy was on the "bad astronomy" forum.
Richard D. Stafford, Ph.D. in theoretical physics.
Andre,
I read the references you mentioned. I still find the subject to be well out of my expertise but you did clear up the fifth power thing. I thought you were saying that the complete effect itself went as the fifth power which is not what you actually said.
I noticed that some of the comments you received from others were somewhat simple minded. In particular, that guy who worked with brakes. He misses some very important differences between his model and the model you are discussing. First of all his model has both components spinning on exactly the same axis which misses the central point of your presentation; but, more important than that is the fact that the circumstances you are talking about allow for much more complex interactions.
One effect which immediately occurred to me (and you are probably well aware of it) is that the connection of the outer solid shell to the inner solid sphere is made via a liquid. That liquid need not at all be flowing in a laminar flow perpendicular to r; in fact, I would doubt that such a laminar flow would even be stable.
If the flow is in rotary cells with the axis of rotation of the cell somewhat parallel to the axis of rotation of the solid bodies (which seems to me to be a very reasonable model) then the liquid can be seen somewhat as viscous ball bearings between the two solid pieces. If that is the case, then there is a very simple interaction which is rather interesting. (Sorry if you have already thought of this.)
First of all, the material being transferred from the liquid state to the solid state at the surface of that interior sphere certainly should not be expected to transfer a lot of angular momentum as the relative motion between the two is not particularly great. Secondly, if the interior sphere, as it solidifies, shrinks (and here we are talking about the interior sphere plus the portion of the liquid essentially moving with that sphere so the shrinkage should be greater than in the simple model) then the rotation rate of the interior sphere would increase (conservation of angular momentum) and the result would be to decrease the rotation rate of those rotating cells. Thus the faster rotating core sphere would actually become a drag on the rotating cells (since they are rotating in the opposite direction).
Another effect would be an expansion of the rotating cells and internal angular momentum conservation would, in that case, augment the slowing of that rotation, further increasing the difference between the surfaces in contact. The net effect of the whole thing would be to reduce the angular momentum of the outer shell and the interior sphere (at that point, the rotating cells would be rotating too slowly).
Now what I have just described seems to violate conservation of angular momentum but it doesn't. Here we merely have four different components and the angular momentum of the rotating cells must be in the opposite direction from the angular momentum of the outer shell and the inner sphere (note that the angular momentum of the liquid divides naturally into two components: rotation of the cells themselves and movement of the cells around the inner sphere). This angular momentum arises directly from the difference in rotation of the two solid bodies which arose because of precession differences (also notice that it really need not be that high and that the movement of the cells plays a small role though it may represent considerable angular momentum, it has little direct effect other than to hide that momentum from view).
It also seems that, as the centers of the rotating cells must average the rotation rate of the two solid bodies, it must also (in the long haul) transfer angular momentum to the other portions of the system.
It seems to me that it follows that the mechanism of differential precession can yield no result except dissipation of angular momentum. Sorry if I am pointing out things you already knew.
Have fun -- Dick
PS -- Yes, I agree with you that mere shifting of the axes caused by precession yields dissipation of angular momentum (transfer of angular momentum away from the rotating mode of the planetary system itself). What I am arguing here is the fact that long term dissipation is the only possible outcome of the interaction: i.e., return of the initial condition (axes once more being aligned) cannot possibly restore the angular momentum vector to its original value.
As I said, I don't think I am telling you anything you didn't already know but rather, I think it is a simple way to see the outcome of the physical interactions. Under ordinary circumstances, evolution of angular momentum transfers can be quite counter intuitive.
Have fun -- Dick
Here (http://www.badastronomy.com/phpBB/viewtopic.php?t=12818&highlight=) is Andre's thread on his idea re Venus, over at the Bad Astronomy forum.
Thanks DrDick.
The rotating convection cells model for the outher core of the Earth is currently the basis for the geodynamo idea (http://www.es.ucsc.edu/~glatz/geodynamo.html). Now, I gues that if the spin axes of mantle shell and inner core diverge, the rotation of the solid masses will impose unusual forces upon the rotating fluid cells, this will result in more "counter-intuitive" precession dynamics and I would not expect the solid parts to continue their rotation unaffected as usual, as if nothing is going on.
If we can accept that, then maybe we could also accept some ideas about the Rapid True Polar Wander on Earth.
A little bit more proof for the Venus story. If the big brake is true, the heat generation of the Planet is not constant. It must have increased first until the planet practically melted and after that it must have been reducing continuously. This would translate to a lot of Volcanic activity earlier on, decreasing gradually when the planet cools. That is of course if there is no tectonic activity, inducing more volcanism.
So how about this:
Basilevsky, A. T. and J. W. Head III
Venus: Timing and rates of geologic activity
Geology 30, 1015-1018, (2002).
http://www.planetary.brown.edu/planetary/documents/2755.pdf
ABSTRACT
We employ the accumulation of the impact-crater population as a geochronometer to examine the observable record of the history of Venus (,1 b.y), analyzing age relationships between craters and the different geologic units. We show that the earlier suite of units (from heavily deformed tesserae through slightly deformed regional plains) occurred during a time period an order of magnitude shorter than the subsequent period (from the end of emplacement of the wrinkle-ridge network until the present). These results imply high global rates of endogenic (volcanic) activity during the first era (comparable to that of mid-oceanic-ridge volcanism of Earth) and much lower global rates of endogenic activity (by two orders of magnitude) for the second period.
Another interesting publication of the same duo:
The surface of Venus (http://www.planetary.brown.edu/planetary/documents/2875.pdf)
Basilevsky, A. T. and J. W. Head III
Reviews on Progress in Physics, In Press, 2003
Perhaps a little prediction is in order. As the earlier volcanism was to be under much hotter conditions, there must be evidence that the odest lava was also the least viscuous. So the smooth lava lakes and the longest lava flows of several thousand miles are likely to be the oldest signs of volcanic activities. Now, let's find evidence for that.
NileQueen
May6-04, 03:21 PM
I am thinking about rotating convection cells in the sun. Gases can behave like fluids. And I am thinking in terms of magnetic implications rather than mechanical ones at the moment. (The sun reverses its poles every 11 years)
http://www.discover.com/issues/may-04/features/here-comes-the-sun/?page=4
Abstract is all you can see of this article but I have the hard copy magazine.
"The sun appears to have hundreds of thousands of flickering lights on its surface. Each flicker, called a granule, is a column of gas about 600 miles wide which vibrates up and down about once every five minutes. Think of each one as a 600-mile-wide drumhead and you can understand why the sun is a noisy place."
Are there correlations in behavior (movement)between these hot gases and the hot liquid in the earth's core?
NileQueen
May6-04, 03:47 PM
Andre: So the smooth lava lakes and the longest lava flows of several thousand miles are likely to be the oldest signs of volcanic activities. Now, let's find evidence for that.
Lava has different properties depending on its composition. Hawaaiian lava tends to not be explosive.
http://www.geo.cornell.edu/geology/GalapagosWWW/LavaTypes.html
"Aa forms when lava flows rapidly. Under these circumstances, there is rapid heat loss and a resulting increase in viscosity."
http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html
Alkali-rich lavas are often charateristic of the waning stages of volcanism, as demonstrated, for example, in the late-stage parasitic cones and flows found on Hawaiian shield volcanoes. Differentiated trachytic and phonolitic lavas typically erupt as low-volume flows with high aspect ratios, as demonstrated above in the phonolite coulées of western Saudi Arabia. However, extensive sheetflows of similar lavas have been recognized in continental rift zones, as exemplified in the voluminous phonolitic lavas of the Ethiopian rift system.
Volumetrically, most lava is of basaltic composition. Basaltic melts have overall lower gas contents and are more fluid than their andesitic-to-rhyolitic counterparts. Their higher fluidity (lower viscosity) is a product of their lower SiO2 (silica) contents. When gases exsolve from basaltic melts they are allowed to rise unimpeded through the fluid magma without a significant build up of gas pressure. This results in relatively calm, nonexplosive eruptions, and a preponderance of lava. In contrast, when gases exsolve from felsic magmas, their upward mobility is impeded by the high viscosity of the melt. This results in the buildup of gas pressure, which generates explosive eruptions associated with a preponderance of pyroclastic ejecta. The low viscosity of basaltic lavas allows them to be extruded over great distances, often producing high-volume lava flows with low aspect ratios (ratio of thickness to area). Under the right conditions, de-gassed felsic magmas can also erupt lava in a nonviolent manner. However, felsic lavas tend to be much thicker than basaltic lavas and have much higher aspect ratios.
http://www.geology.sdsu.edu/how_volcanoes_work/Lavaflows.html
Is the silicon percentage of Venus known?
NileQueen
May6-04, 03:54 PM
http://www.cotf.edu/ete/modules/volcanoes/vtypeslava1.html
Here is a good illustration.
Good points, your Majesty
Obviously, we have to compare the same type of lava in the different eras. I doubt if we have enough information about that already. So, it may be a real, open prediction. Those are the best.
Let's have a closer look at the cracks at Venus (http://spaceflightnow.com/news/n0103/13venus/).
A mathematical model of the surface of Venus could show how the hot, dry surface has reacted to changes in temperature throughout the planet's history
And sure enough, here (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?2002JGRE.107k....8S) is an abstract of the result:
The climate change-induced scenario is consistent with many characteristics of the polygons, including the small and large size ranges, the compressional ridges, and their occurrence with and without evidence of local heating. Although polygons may have diverse origins, including formation by multiple deformation events, overall polygon characteristics support the climate change hypothesis.
I wonder if we can find more details. I do have my doubts. From the first link:
This kind of cracking pattern shows that the surface has heated and cooled by almost 200 degrees Celsius (392 degrees Fahrenheit) over long periods of time.(...)
(...)Slow heating and cooling globally could have formed large areas of cracks on Venus' surface.
I don't think so. Why?
This pattern of cracking can be seen in drying mud on a dry lake bed, on old paintings, cooled lava flows and on mishandled pottery. There is actually a special technique ("Raku") to get those cracks on pottery glacing. Whilst after baking, normal pottery needs to cool off very slowly to avoid the cracks, raku implies cooling the ceramics with water quickly immediately after the baking.
What is the common denominator here? the surface of the object shrinks whilst the underground does not, at least not with the same rate. Paint and mud evaporate solubles and water and are shrinking consequently. Lava and glazing of pottery cools much more quickly than the layers underneath and hence shrink. In al case the underground maintains it dimension, forcing the surface to crack up.
Are we seeing the same here on Venus? This implies that the Planet has been heating itself from underneath after that the cooling was fast enough in these areas to cause those cracks. This would support the big brake hypothesis.
Slow heating or cooling is not typically for causing these cracks. Moreover identifying a temperature range for these cracks as 200 degrees seems not logical. It's not absolute temperature but rate of temperature change that causes these cracks, or the quick cooling after the big brake heated the planet.
NileQueen
May10-04, 10:46 AM
Yes, how can we replicate such large cracks?
I think on the pottery it is stress fractures from extremes of temperature (water on hot glass) and the material cannot adapt quickly enough throughout
NileQueen
May10-04, 10:49 AM
If the expansion were due to gases (thinking about possibilties in the hot surface, as the surface cooled we might see a pumice type effect.
Is there moisture involved that dissipates? Liquid or gas? Perhaps the high pressure (of Venus' atmosphere) has something to do with the larger scale cracks versus the smaller scale cracks (Giant's causeway has those very uniform polygons)
NileQueen
May10-04, 10:51 AM
A hot body in a high energy state (thinking of a planet in a near melt-down state) would expand, and as it cooled it would contract...
NileQueen
May10-04, 11:10 AM
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1934.pdf
Mantle plume events and grabens...
NileQueen
May10-04, 11:13 AM
low water/low silica would give a non-explosive, runny lava
low water high silica would give a non-explosive but thicker lava
But that is under earth-like conditions....
NileQueen
May10-04, 11:22 AM
Do we see similar cracks anywhere else in the solar system, or on earth?
Working on the paper now. 8 pages for 50%.
An important modification is the application of the chaotic motions in the solar system, (http://www.imcce.fr/Equipes/ASD/preprints/prep.2003/th2002_laskar.pdf) and the resonance between obliquity and precession cycles in the chaotic zone. This may have changed the obliquity of Venus substantially and at accellerated rates. This would facilitate the deviation of spin axes between mantle and the "stubborn" inner core.
I have a feeling that the idea has a firm basis now.
woodysooner
Aug4-04, 01:36 AM
is the paper finished, and where do you goto school you sound super smart not to give you a monster head lol. are you astrophysist??? or what would they call someone like you, or are you done with school, and teach???
Well the paper is about finished, say 95%. About 30 pages now. But I need an expert opinion first.
No I'm not an astrophysisist, actually I'm a retired fighter pilot and just a guy toying with ideas a lot.
Ok, here's the real skinny on Venus. The planets are evolving due to gradual loss of heat. Mars was furtherest from the sun; it cooled to it's life giving time first. Earth was then like Venus is now. As the planets cooled, mars became too cold; earth cooled into the life giving time. As earth cools to be like mars, Venus will cool to it's life giving time :smile:
Works for me.
Keep on chuggin !!
Vern
Just another update, since I get the impression that others also believe that we might onto something.
The manuscript keeps growing. The current draft is about 95% ready and comprises 20.130 words on 43 pages (pitch 12). I expect it to grow another 2000 words in the next few weeks. The lastest addition on ideas is the problem of the missing oxygen. Anybody like me to elaborate on that?
Anyway this is the outline:
Prologue
ABSTRACT (to be finalized)
PREFACE (ready)
A quick introduction
A Little Philosophy
Methodology
EVOLUTION OF THE SPIN OF VENUS (ready)
Initial Spinning Conditions
Evolution of Planetary Spin
Orbital Variations
Precession of the Equinoxes
Precession of the Perihelion
Obliquity cycle
Orbital Eccentricity
Chaotic Zone
Venus and the Chaotic Zone
THE BIG BRAKE HYPOTHESIS (ready)
ATMOSPHERE AND CLIMATE (ready)
Runaway greenhouse model
Wet greenhouse model
The missing oxygen problem
Retrodicting the big brake
VENUS SURFACE (ready)
Surface composition and features
The age of Venus’ surface.
THE HEATING AND COOLING OF VENUS.
Lacking magnetism (ready)
Tectonics (working)
Venus gravity. (ready)
Resurfacing or solidifying? (working)
DISCUSSIONS AND CONSIDERATIONS (ready)
Preservation of Momentum
Why (not) on Earth?
REFERENCES (but actually coauthors) (working)
Perhaps one more key point of discussion is the problem of conservation of angular momentum. It seems rather counter-intuitive that the angular momentum of the planet stored in it's spinning is totally gone, while the law of conservation of angular momentum (http://theory.uwinnipeg.ca/physics/rot/node7.html) goes like:
In the absence of external torque, the angular momentum of a rotating rigid body is conserved or
For systems that consist of many rigid bodies and/or particles, the total angular momentum about any axis is the sum of the individual angular momenta. The conservation of angular moment also applies to such systems. In the absence of external forces acting on the system, the total angular momentum of the system remains constant.
Note:
Angular momentum and torque are really vector quantities. Their direction is always along the axis of rotation.
emphasis mine and these are the two key players in the case of Venus.
I said earlier:
Another issue is conservation of momentum. Any hypothesis dealing with the loss spin of Venus should deal with that. With gravitational interaction, transfer of momentum may take place with the sun, equivalent to the Earth-moon interaction and The vector sum of the individual momentums decreases during the process of diverging of the spin axes again caused by gravity interaction with the sun.
Let us look at Earth's precession. the Earth spin axis follows a cone to be completed in only about a mere 26,000 years. This is caused by an external torque force imposed on Earth due to the equatorial bulge (http://www.geol.binghamton.edu/faculty/barker/demos/demo10.html). What does this do to the constantness of the Earth angular momentum/ Nothing? forget it. Angular momentum and torque are really vector quantities. Their direction is always along the axis of rotation..
So the torque force of Sun and Moon on Earth is big enough to change the direction of the spin axis (and consequently the vector direction of the angular momentum) to over about 47 degrees in only 13,000 years (opposite sides of the precession cone (http://www-istp.gsfc.nasa.gov/stargaze/Sprecess.htm)). When doing a three directional vector analysis we see that the vector components of Earth angular momentum have changed considerably, although the absolute value of the vector sum remained constant.
Now image that only the Earth mantle spin axis was doing this precession movement, whilst the core remained fixed, then the individual angular momentum vectors would start to diverge unter the influence of the precession of the mantle caused by the gravitational torque.
When the mantle spin axis arrives at the opposide side, the absolute value sum of both components would be still the same. However the absolute value of the vector sum would be less, since both vectors diverge. So if at this point, for some reason the internal friction would force a realigment of both spin axes the total vector sum of both components would apply and consequently the absolute value of the resulting momentum (lenght of the vector) would be less than the sum of the original two components.
Contradiction to the law of conservation of angular momentum?
No, definitely not, since
In the absence of external torque, the angular momentum of a rotating rigid body is conserved
But there is external torque and a lot, enough to rotate the spin axis of the Earth effectively 47 degrees in as little as 13,000 years.
Another element is that the transfer of Angular Momentum -due to that torque- is a continuing process, not restricted to those periods of those hypothetically chaotic realigments of spin axes that apparantly reduce the angular momentum on that moment. The vector sum was reduced already during the precession process, although the sum of the absolute values of the seperate elements remained the same.
So how about Venus? lacking a robust moon, the only effective torque provider for the required precession seems to be the gravity of the sun. Question is if this torque force could approach that on Earth. It must be quite some math to work this out exactly but I still have that old envellope.
Using good old Newtons universal law of gravity, we can quickly calculate the gravity difference (proportional to the torque) on the near side and the far side of the planet, filling in for R(radius): the distance between the solar bodies plus and minus the radius of the planet. Then if we calculate this in case of Earth - Sun and take this as a unit, we see that Earth - Moon is about 3,5 torque units and Venus - Sun is by the same method still slighly over 2 units. Not nearly as low as we may have estimated.
Concluding, the gravity interaction between Venus and Sun approaches the order of magnitude of gravity interaction between sun/ moon and Earth and hence a hypothetically oblique spinning Venus with an equatorial bulge would have been subjected to precession due to solar gravity torque forces, albeit less than, but still comparable to Earth.
And torque forces interchange angular momentum between bodies. Angular momentum remains constant but this goes for the sum of all angular momentums and not an isolated planet. So, it seems to be possible to halt the planets spinning by repeating those steps of diverging spin axes over and over and over (there have been a lot of 26,000 year cycles in 4,6 billion years). Eventually, all angular momentum could have been converted to other solar bodies.
Convincing?
Bystander
Nov12-04, 03:18 AM
(snip)This is caused by an external torque force imposed on Earth due to the equatorial bulge[/url].(snip)
Someone's invoking an unnecessary condition for precession of spinning bodies in gravitational fields of other bodies --- bottom line? If it spins and is in a field with a non-zero gradient, it precesses --- that's "mantle" and "core." With or without tidal/equatorial bulges.
I don't know Bystander
I had some sources (http://aa.springer.de/papers/7318003/2300975/sc2.htm) for this assumption.
The equations of precession of the Earth are derived from a Hamiltonian function H which is the sum of the kinetic energy and of the potential energy of the torque exerted by the Sun and the Moon on the equatorial bulge of the Earth.
..... cont
Well today I had my first refusal for publication. "Sorry, we decided not to be interested after consulting some editors". Or between the lines: "we don't deal with crackpots". What else could you expect I guess. So perhaps continue to exchange thoughts. How about the lacking magnetism perhaps.
Long time ago (page 1) Jonathan posted a real gem:
Maybe the liquid outer core of Venus has become solid, leading to a callapse of the magnetic field and all sorts of directly related enviromental cataclysims. Though I don't think that would explain why it rotates so slowly. Would a solidification of the liquid outer core affect volcanism? It seems like it would, and though I'm not sure I think Venus' volcanism is dead or dormant, maybe thereby proving it's inner/outer cores have solidified into one. ....
Thanks Jonathan. I guess you may very well be right on those counts. I'm certainly using it extensively in the hypothesis - if you don't mind. I'd be happy to take it as ref.
Any further thoughts about that?
Suppose that the interior of the planet would have cooled because it lost it's heating device like on Earth perhaps core - mantle friction, generated by precession. Can we find out more about that?
For instance what do we know about the thermal gradient of the planet, or the rate of temperature increase with depth?
In this paper (http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1996LPI....27..169B&data_type=PDF_H IGH&type=PRINTER&filetype=.pdf), Grimm et al content that the thermal gradient of the oldest terrains (Tessera) had a thermal gradient that exceeded 25 degrees Kelvin per kilometer while the youngest feature, the Artemis Chasma, has a thermal gradient of below 4 degrees Kelvin per kilometer.
very puzzling, if you don't know about the big brake.
Now here is somebody who would likely tend to agree with me:
http://arxiv.org/ftp/physics/papers/0502/0502135.pdf
The source of the Earth's activity lies in the difference of the angular velocities of the mantle and of the solid inner core. The friction between both spheres infers heat, which is the
cause of the melted iron which constitutes most of the liquid outer core, as well as the source of the global heat flow. The solid inner core angular velocity is supposed to remain steady, while
the mantle angular velocity depends on gyroscopic forces.....
....The rotational axes of the inner core and of the mantle may be different. Particularly the one of the mantle may be variable ; this mantle, indeed, is more sensitive than the solid inner core to the various external attractions coming from the Solar system, because it "floats" above a liquid.
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