Floating Venusian cities or Venus vs Mars vs Titan revisited

StarDreamer · 2007-06-05 18:28:50

Don't stop there. I didn't mean an alternative Earth. Just use Earth in place of Venus, to use what we know applied to "terraforming Venus." Would it even be feasible to sustain life with such a rotational configuration. (What could have caused it, by the way, and what a damn shame it turned out the way it did.)

My guess: It is not actually spinning retrograde. It is spinning prograde, but with its north pole pointing the wrong way (upside down). Uranus got knocked over on its side by a colossal impact. Venus got upended. Tidal drag vis-a-vis the Sun has not helped either.

nickname · 2007-06-05 18:47:15

dicktice,

Ahh an Earth in the location of Venus.

At one Bar of pressure with Earth and moon together as a pair

Earth in the location of Venus wouldn't be as bad off as the original Venus.
I believe it is life that just made it in time on Earth to avoid the same runaway greenhouse Venus had.

Earth in the location of Venus would endure very high hot spot temperatures in the 80 - 90c range on the equator, with at least twice the sunlight clouds would be more than twice what we have on earth due to extreme evaporation cycle.
This also means extreme rain activity, maybe all the time or most of it on most of the globe.

A hot wet place with little direct sunlight making it to the ground.
Less sunlight also means less ability for life to recover from volcanic activities and less ability to store carbon away.

This might be what got Venus into trouble, with a few bars of pressure on Venus the Earthlike place, it held more h20 vapor in its atmosphere and hot spot temperatures near 100c, with a boil point of water at 102 or 103c.

One long volcanic epoch and Venus was on the no return to runaway greenhouse with boiling water on hot spots and escaped co2 and h20 as steam increasing the greenhouse.
Lost Hydrogen to space made it even easier for c02 to form in the atmosphere.

My guess for Venus and the backward spin....
A similar size object impacted Venus early on, unlike Earth getting a moon with a glancing blow with it's huge impactor, Venus just got a thump almost directly on.
This is also a good explanation for such a similar sized world to have near 0 magnetic field, no rotation of the core either when the 2 cores became 1 on a direct impact.
Earth was lucky and retained its core spin when the Big impactor that formed the moon hit Earth without destroying Earths core or it's movement.

Spatula · 2007-06-07 16:31:25

Don't stop there. I didn't mean an alternative Earth. Just use Earth in place of Venus, to use what we know applied to "terraforming Venus." Would it even be feasible to sustain life with such a rotational configuration. (What could have caused it, by the way, and what a damn shame it turned out the way it did.)

It's difficult to say what the temperature of Earth would be in Venus's orbit. The most optimistic estimate I heard was 36 degrees Celsius. Uncomfortably hot but possible to live in. We might be able to artificially bring it down.

I would recommend looking at this site, as it does a good job explaining how all this temperature stuff works.

Note that the surface temperature of Venus without an atmosphere is not known. If the surface is 30% reflective, like Earth's, it would be around 25 degrees Celsius already, compared to Earth's -17. Earth's atmosphere adds 32 degrees to its temperature, bringing it to 15 degrees. Earth's atmosphere around Venus would then supposedly bring it up to 57 degrees.

I'm pretty sure 57 is the average temperature Nickname is using, when he talks about a boiling equator.

Make no mistake, a 57 degree planet would not be fun, though unlike Venus now it would actually be a plausible world to live on. Just build surface structures that create shade, and the area under them would instantly fall back to earth temperatures. An ecosystem could be engineered to survive this hot world. If this were the end-product of terraforming Venus, it would still be worth it.

This is probably not a correct estimate of Earth's temperature in Venus's orbit though, because it simply assumes that the amount of water in the atmosphere will be the same. Obviously, if you're hot enough to boil the oceans off, that's not going to happen. The extra heat would spread more atmospheric water into the upper atmosphere, forming a larger amount of cloud-cover, and reducing surface temperatures.

On top of that, an atmosphere with the same composition would be more reflective at higher temperatures, due to its changing specific heat.

These should bring the average surface temperatures down to around 36 degrees celsius, which is still quite hot, but good enough. This is what we're aiming for. This would be Earth in Venus's orbit.

The slower spin, lack of axial tilt, and thicker atmosphere (3 bars of Nitrogen) will all change Venus's temperature with respect to Earth's, probably lowering it some extent. Especially the slow rotation. All the clouds forming on the sun-facing side of the planet would not last long enough to insulate temperatures on the night side of the planet, making it significantly colder on that side than normal.

nickname · 2007-06-08 06:29:52

Spatula,

You have hit on the same catch 22 that has always puzzled me on how Venus got the way it is.
I've read quite a few papers on the topic, but they always leave gaping holes in the explanation of how we get to what we see.

More sunlight and higher pressure means higher temperatures, but it also means more cloud and lower temperatures and a slow c02 scrubbing from rainfall.

A global offset and cooling should have occurred on Venus as it got hot enough to form thick layers of clouds from the water vapor.

Even with a very think atmosphere i can't quite get the water to boil away on Venus to form what we see today.
I can get small areas to boil at 2 to 5 bars with huge oceans, but it just contributes to the cloud cover.

Maybe the chemistry of Venus has more to do with the lack of magnetic field than anything else.
Or Venus just didn't have that much water to begin with.
Or when the two impactor worlds collided its pretty much was the way we see it now.

I also think about 57c as the temperature on the equator.
The cloud cover produced from the wetter thicker cloud covered atmosphere would point to your lower temperature of about 36c almost everywhere on the globe.

If we have good sunlight in spots and additional 25c or so just in local spots, on perfect hot sunny days getting near 90c in small locations.

Not much hope of having good sunlight on even the teraform Venus surface though

StarDreamer · 2007-06-08 07:03:51

Are the cloud layers at different altitudes on Venus chemically different? I understand that the upper cloud deck has the water vapour (such as it is) and sulphuric acid (H2SO4). What is in the lower layer? What constitutes the obscuring component of the clouds at each level?

Spatula · 2007-06-08 11:51:23

Water exists only in trace amounts in Venus's atmosphere. However, there's an awful lot of atmosphere, so the amount of water there could prove to be the proper amount a planet that close to the sun should have.

I'm banking on Venus never having enough water in the first place.

If it had Earthly amounts of water on it, where did it all go? Photodisassociation leaking hydrogen into space? If that were so, we'd see a lot more oxygen in the atmosphere, yet there is none. Plus, you would still see more water. Venus has 93% of Earth's escape velocity, so it does a pretty good job keeping water vapor from breaking up.

This explanation also seems to be a concession that there was always a thick atmosphere on Venus. If it were ever able to form standing oceans, it would become very difficult to destabilize the climate as it has been. Oceans act as a CO2 sink. Dissolved CO2 would be recycled into the mantle in areas where crust was subducted. Our most widely accepted model of Venus's geology shows tectonic plates completely renewing the surface in intervals every 500 million years.

RobertDyck · 2007-06-08 12:31:53

Spatula, Venus has more water than you think. The planet is enclosed in a solid cloud layer; it is clouds like on Earth but there are no breaks. However, since the surface temperature is +850°F at the coolest point, there isn't any liquid water near the surface; all the planet's water is in its clouds. That said, if it were to all rain down Venus would still be a desert.

And those rain clouds do rain. The clouds form where pressure is about 1 bar; Earth at sea level is 1.01325 bar and the clouds form at altitudes where pressure varies more than 0.1 bar, so that's about the same as Earth. Temperature is about 0°C (freezing), but again the bottom of the clouds have higher pressure and temperature while cloud tops have lower. Rain does fall but while those rain drops are still tens of kilometres above the surface it encounters air +100°C, so the rain drops literally boil away in mid-air. Rain never reaches the surface.

Pioneer Venus was a NASA orbiter sent to Venus. It measured hydrogen flowing off the night side of Venus still today. The magnetic field of Venus is so weak it's practically non-existent. Solar wind impacts the upper atmosphere directly. That breaks water molecules into hydrogen and hydroxyl (OH) groups. Some of those free hydrogen atoms are struck so hard by solar radiation that they achieve escape velocity. I could get into other chemical reactions and intermediate steps, but the result is breaking water into hydrogen and oxygen. The temperature and pressure at the surface is enough for CO2 to combine with sulphur to form carbonyl sulphide (COS). That's a stronger corrosive than sulphuric acid. It only exists in the lower 30km of the atmosphere, above that it breaks down. COS will combine with oxygen to form carbon dioxide and sulphur dioxide. As you know when sulphur dioxide combines with water in the tops of clouds together with ultraviolet light from sunlight, it forms sulphuric acid. What you may not know is there isn't any sulphuric acid near the surface, acid rain can't get down that far. However, the COS is worse.

The point is we know where the water went; solar wind broke it into hydrogen and oxygen. The oxygen stayed but hydrogen was blown into space. Hydrogen is still flowing off Venus into space to this day.

Spatula · 2007-06-08 14:57:32

Put very eloquently, and if I didn't already know that the deuterium to hydrogen escape ratios didn't support your claim, I would probably agree with it. There are two models for outgassing that the Pioneer data supports, and neither is conclusive. It'll have to wait until the next barrage of probes to be resolved.

And no, Venus does not have more water than I think. Water is only .002% of the atmosphere, 18.6 kPa. A pitifully small amount compared to Earth's total hydrosphere.

I'm willing to bet it never had much water. That the current atmospheric level has been stable over long time periods, renewed through geological processes and comet deposits. The complete lack of any atmospheric oxygen would seem to support this. Stellar evolution predicts a lack of water. And the abundance of CO2 is better explained through other processes.

RobertDyck · 2007-06-08 16:53:46

Also eloquently put. Do you have a reference for "deuterium to hydrogen escape ratios"? The data I read from Pioneer Venus indicated hydrogen loss continuing as Pioneer Venus orbited.

nickname · 2007-06-08 17:45:58

Spatula,

That would be my first guess is that Venus never had that much water.
If it did we would probably still see the wet hot rainy world.

The only other way i can see getting entire oceans to boil away is if the entire surface of Venus was molten, that might do the trick to turn ocean into 92 bars of C02.

Yet the length of time required to turn that much water vapor into escaped hydrogen and free oxygen that bonds with free Carbon would be longer than the sun has existed.

I think we are left with It never had water quantities like Earth, or early on a massive impactor/collision created pretty much what we see.
That would explain a few oddities on Venus spin and magnetic field also.

I can understand what Robert is trying to say, it works well for explaining the c02 content of Venus, just not well to explain how we get to extreme temperatures in the first place before that chemistry begins.
Creating those boiling oceans to start that process is the problem.

RobertDyck · 2007-06-08 19:58:11

The theory is that all terrestrial planets, including Venus and Earth, started with thick CO2 atmospheres. Mars didn't get as much because it's a smaller planet, but it had more than now. The sun was very hot when it was young, then cooled. As it cooled, Mars was furthest so it had liquid oceans first. As the sun cooled further Mars froze, the winter pole is colder than the freezing temperature of CO2. Mars atmospheric pressure is the equilibrium between dry ice and CO2 gas at the winter pole. During half the Martian year it's the south pole, during the other half it's the north pole. Then Earth cooled to permit liquid oceans. Earth had a CO2 atmosphere, but it's CO2 dissolved in the ocean where it interacted with dissolved calcium to become calcium carbonate (limestone). Eventually life formed, and it developed to precipitate calcium carbonate as it's shell or skeleton. Probably life first used inorganic precipitating calcium carbonate, then controlled its formation, then actively created calcium carbonate. In later eons life drove the creation of calcium carbonate. This resulted in dramatically reducing Earth's atmospheric pressure by turning its CO2 into solid rock.

Venus started with atmosphere almost identical to Earth. However, while Earth had a strong magnetic field, Venus had a very weak one. The theory is solar wind impacted the upper atmospher breaking water molecules and accelerating light gasses to escape velocity. Hydrogen is lightest, it escaped into space. CO2 is a greenhouse gas, it trapped heat in. Actually, the surface of Venus today is hotter than Mercury. But the theory is all 3 planets started too hot for liquid surface water. The freeze/thaw cycle regulates temperature on Earth today, but ocean currents also help transport heat between poles and equator. Venus doesn't have any of that, and doesn't have life interracting with environment. Venus has a runaway greenhouse effect. The crushing pressure and baking heat keep the crust thin and hot. Volcanoes cannot form high mountains because rock is too soft, it flows into low forms.

You see it doesn't require a molten surface, and all 3 planets started with a lot of CO2, Earth had as much CO2 as Venus has today. Venus never lost it's thick CO2 because significant gravity, lack of an ocean, and proximity to the sun. It never got an ocean because of proximit to the sun, and lack of a strong magnetic field.

Spatula · 2007-06-08 23:41:24

http://adsabs.harvard.edu/abs/1999Icar..141..226D

Venus is losing water, but it's losing water too quickly. The current water in the atmosphere is probably recent, because if most of it had been eliminated, there would be much more deuterium in it. Some more evidence for the intermittent periods of plate tectonics. The possibility is also brought up that it simply doesn't lose water this quickly most of the time.

Possibly a magnetic field that is simply undergoing a pole reversal right now? Or a field that has much longer dormant periods? I'd like to think that, but the prevailing attitude is that it had a strong earth-like field for the first billion years or so, and a gradually weaker field until 800 million years ago. http://www-ssc.igpp.ucla.edu/personnel/ … venus_mag/ this talks about that. Seems a field over much of its geological history would preclude your explanation for out-gassing. Though a dynamo is not going to stop the process of hydrogen loss. It happens on Earth.

That would be interesting news to find out, but we won't know that until we've studied the planet's internal structure more. Right now we only have fuzzy gravity data and inferences based on what a planet 'sort of like Earth' should act like.

RobertDyck · 2007-06-09 01:45:08

Venus is losing water, but it's losing water too quickly.

Ah hah! Now we're getting somewhere. Our difference is not the data, it's the conclusion. Venus is loosing water so fast that starting with similar water to Earth would have resulted in no water long ago, hundreds of millions of years ago. The reason there's water at all is attributed to new water released by volcanic outgassing.

You're concluding (or reading conclusions) that make a guess the magnetic field wasn't always this weak. But there's no evidence to support that. Mars, Venus, and Mercury all have very weak magnetic fields. Only Earth and the gas giants have strong magnetic fields. That has been attributed to our moon. I could give you my theory why our moon causes a strong magnetic field, but it's my idea. What has been accepted by scientists is simply that it does. The orther rocky planets in our solar system don't have a large moon, hence no strong magnetic field.

nickname · 2007-06-09 04:06:48

RobertDyck,

I have no problem with the rate of water loss on Venus.
Earth gets water added to it all the time, so Venus should also receive about the same.
If we boil away all the water earth receives each day it would nearly account for the losses we see at Venus.

The chemistry is pretty straight forward on what happens to boiled water on Venus with little magnetic field.

The chemistry to get the ocean water boiling isn't.
If we think of Venus as a similar place as earth with maybe 5 - 10 bars of pressure and similar water totals on Earth as oceans.
The current C02 atmosphere data would state that 59 bars of 02 was originally water, making a total of around 80 - 90 bars of h20.
Similar to earths total or maybe even more water.

I can't get the initial ocean boil to start on Venus even with a sun 25% hotter.
All you get is very thick reflective clouds and heavy rain.

Your idea of a crust that never cools is an interesting one.
If Venus was always to hot for liquid water at the surface, then arriving at the Venus we see today is quite possible.
Difficult to explain how we got to 89 bars of C02 and 3 nitrogen without oceans but not impossible.

Oceans with a long volcanic epoch might be another method to get past the boil point of an ocean, or just a collision with another large body.
Those are both easy ways to convert h20 quickly into thick atmosphere and move past the ocean boil/cloud problem.

Venus is an interesting place however it turns out.

I also agree that our moon is more important to our magnetic field than credit is given.
Just is.. just wont do

Spatula · 2007-06-09 10:48:02

Venus is losing water, but it's losing water too quickly.
Ah hah! Now we're getting somewhere. Our difference is not the data, it's the conclusion. Venus is loosing water so fast that starting with similar water to Earth would have resulted in no water long ago, hundreds of millions of years ago. The reason there's water at all is attributed to new water released by volcanic outgassing.
You're concluding (or reading conclusions) that make a guess the magnetic field wasn't always this weak. But there's no evidence to support that. Mars, Venus, and Mercury all have very weak magnetic fields. Only Earth and the gas giants have strong magnetic fields. That has been attributed to our moon. I could give you my theory why our moon causes a strong magnetic field, but it's my idea. What has been accepted by scientists is simply that it does. The orther rocky planets in our solar system don't have a large moon, hence no strong magnetic field.

We can't really conclude anything about the past water based on current water.

It's very likely Venus had a magnetic field for most of its past. There are many competing explanations for why it doesn't have one now. Some guess there's no solid inner core, some guess everything's there but there are no currents due to the harder, colder nature of Venus's crust. That's probably the most compelling explanation, but if it were true, it would lead to a planet that was magnetized for most of its history, and still develops occasional pole moments with long periods in between.

Sure the moon helps, but is not essential. It wasn't a deal breaker for Venus. Mercury's 1% field flies straight in the face of that claim.

RobertDyck · 2007-06-09 14:51:37

My hypothesis is that gravitational tides do it. Gravity causes not only tides in the ocean, it also causes the crust to flex. It isn't as much as ocean water, but it does happen. That has slowed the rotation of the Earth, I read one estimate that when the Moon was first formed from the collision of another planet the Earth had an 8 hour day. The Moon was also much closer, causing much more pronounced tides. As the Moon receded the strength of tides lessened, but the period also increased. The Moon is still receding, but very slowly. Tides on the crust cause the crust to slow, but the Moon's gravity doesn't cause the core to close its rotation. The core only slows by friction with the crust. I believe Earth's core is still rotating faster than the crust, and that friction induces an electric current. That differential also organizes mantle convection cells. Normally convection cells counter rotate; the side of two adjacent cells either rises or falls together. However, if the core rotates faster than the crust and the top of convection cells is in contact with the underside of the crust while the bottom of cells contacts the core; that will tend to organize convection cells to rotate together. Coordinated convection cells will add more energy to the dynamo than direct friction.

Then there's Mercury. It's so close to the Sun that it experiences tides. It's tidally coupled; it rotates one and a half times each orbit. To say it another way, its rotation has a 3:2 resonance with its orbit. This demonstrates strong tidal forces on Mercury, although the period of rotation is no longer lengthening. The stability of its resonance will permit the core to "catch up" to its crust, weakening the dynamo. So you see this hypothesis is consistent with Mercury.

Mars and Venus are too far from the sun for tidal effects. But they don't have a large moon, so no tides. I expect the core to rotate in sync with their crust. I also read that planetary accretion models predict some planets won't rotate the same direction as their orbit, some will rotate backward. Also the accretion model predicts relatively slow rotation for rocky planets. Venus perfectly matches these predictions, and Mercury's slow rotation is also consistent. Earth is explained by a Mars size planet that impacted tangentially, most getting absorbed into the Earth making our planet larger and the rest becoming the Moon. The impact left us with a fast rotation, short day. However, this doesn't account for Mars having a fast rotation; I have yet to read a theory why Mars length of day is almost exactly the same as Earth.

Spatula · 2007-06-09 16:30:32

The default rotation would be tidally locked with the Sun. Collisions speed it up or slow it down.

Mars and Venus show evidence of large collisions in their past. Venus probably had a moon early in its formation, from something similar to Earth's moon-forming collision. Another collision of a similar magnitude resulted in its retrograde rotation, and this caused any moons formed before or after it to spiral into the surface.

I read an interesting theory that the slow rotation could actually be caused by friction with the atmosphere. It's significant enough to remove a substantial amount rotational energy from the planet. Along the same lines, the slow rotation could be caused by a resonance with Earth. One Earth occultation occurs every 5 Venusian days.

'Catching up' doesn't happen until the core solidifies, which may or may not have happened on Mercury. The real dynamo killer is a lack of convection. The interior is all the same temperature. Probably the case on Mars, and possibly on Venus. All fun things we'll get to find out about in a few years.

StarDreamer · 2007-06-09 22:15:29

And no, Venus does not have more water than I think. Water is only .002% of the atmosphere, 18.6 kPa. A pitifully small amount compared to Earth's total hydrosphere.

Is this including the water trapped in H2SO4 molecules? Sulphuric acid is basically sulphur oxide dissolved in water (H2O + SO2). Actually, it is 2 molecules of water to produce one H2SO4 plus H2, which then escapes. Curiously, according to wikipedia, two molecules of H2SO4 break down into two SO2 plus two H2O plus an O2 at 830*C. Does that temperature sound familiar? That's the surface of Venus.

Maybe incoming ice blocks striking the Venusian atmosphere (as at Earth) are reacting exothermically with airborne sulphur at depth to make the H2SO4 plus free hydrogen ....

StarDreamer · 2007-06-09 22:19:30

Only Earth and the gas giants have strong magnetic fields. That has been attributed to our moon. I could give you my theory why our moon causes a strong magnetic field, but it's my idea. What has been accepted by scientists is simply that it does.

I would like to hear your theory -- please go ahead!

Spatula · 2007-06-09 22:31:54

Is this including the water trapped in H2SO4 molecules? ....

Yes it is including that.

I would like to hear your theory -- please go ahead!

The moon contorts Earth slightly, churning it up. Pretty reasonable. It's based on very well known tidal heating effects of other things. It's been touted that the formation of the moon prevented Earth's crust from having the same thickness as Venus's crust, which could be what is hindering Venus's interior cooling from forming a dynamo.

I would say that's probably right. Personally, I don't think a moon is really necessary for that. The geodynamo just requires a certain size and planetary composition. Getting the moon was just one way for Earth to arrive at that chemistry. But then again, I'm the crackpot who thinks Venus is easier to terraform than Mars. Well, maybe not easier, but the end product would be better.

Maybe he was talking about something else though. I don't know.

StarDreamer · 2007-06-09 22:54:20

The default rotation would be tidally locked with the Sun. Collisions speed it up or slow it down.

Hmmmm ... not entirely. Mercury is tidally locked to the Sun for the same reason that Luna is locked to the Earth -- too close for too long; not enough inertia of its own. Venus had a "handicap" in this regard, but it was not foregone that it would fail this way. As RobertDyck says -- how do we explain Mars? The answer is that distant planets hold their inertia and angular momentum (torque) longer.

Planet formation begins with static electricity in the disk causing local accretions and clumping. Eventually individual clumps get "a leg up" on their neighbours and then the game of cosmic billiards begins. The big get bigger after that. Spin builds through a sort of coriolis effect -- each clump's inner edge and out edge have a speed differential.

Mars and Venus show evidence of large collisions in their past. Venus probably had a moon early in its formation, from something similar to Earth's moon-forming collision. Another collision of a similar magnitude resulted in its retrograde rotation, and this caused any moons formed before or after it to spiral into the surface.

I doubt this. Terrestrial rocky planets tend not to grow coeval moons, while the gas giants do with some uniformity. Mars has only 2 tiny captured asteroids. Mercury and Venus have nothing. Then Earth has this whopping big moon -- clearly an extraordinary situation demanding an extraordinary explanation.

Jovian worlds formed coeval moons because their planetary disks were not disrupted by our evolving star. If they had been close enough to our star for the star to either steal or blow away their gas, then they would also have been close enough for the outer margins of their disks to be disrupted, collapsed (compressed prematurely) or whatever. My instinct says that L1 to the star so compresses the safety zone around the young planet that the gap from L1 to its Roche Limit is too poor in materials for a moon to evolve. Distant planets have more generous L1 points.

So terrestrial planets only get moons by capture or collision. The collision must be of a particular nature for that to work. A direct hit is ultimately engulfed as the planet bursts asunder uniformly or symmetrically and thus reassembles itself, with the orbiting debris infalling. Only a glancing blow shears off enough material with enough force to get it past the Roche Limit. Luna is not the object which hit us -- Luna is our own crust flung into orbit.

StarDreamer · 2007-06-09 23:10:04

Mars and Venus are too far from the sun for tidal effects. But they don't have a large moon, so no tides. I expect the core to rotate in sync with their crust. I also read that planetary accretion models predict some planets won't rotate the same direction as their orbit, some will rotate backward. Also the accretion model predicts relatively slow rotation for rocky planets. Venus perfectly matches these predictions, and Mercury's slow rotation is also consistent. Earth is explained by a Mars size planet that impacted tangentially, most getting absorbed into the Earth making our planet larger and the rest becoming the Moon. The impact left us with a fast rotation, short day. However, this doesn't account for Mars having a fast rotation; I have yet to read a theory why Mars length of day is almost exactly the same as Earth.

Venus actually has a thick crust. It is Earth with the thinnest crust in the solar system! The object which collided with protoEarth did not become the Moon. That was engulfed by Earth itself. Luna is our crust flung into orbit. The composition of Luna is basaltic lava rock -- 100% of Luna matches the "sea floor" rock of Earth, but not inner Earth. In other words, when Earth got hit, it was already a hot molten ball and it had already stratified into layers, with the iron and nickel and radioactive elements sinking into the core while the lighter elements floated in the crust. When the mother of the Moon hit Earth, it vapourised the crust and sent it all aloft. The continental shield lands (like the Canadian Shield -- the cratons I mean) are the survivors who stayed put. The Atlantic has opened and closed many times while the Pacific has existed always. Think about a world with all the high table lands (cratons) huddled together in a global ocean and you will know where that other proto-planet hit us. Also -- the only way many of the cratons fit together properly is if the curvature of the Earth is increased (ie: the planet is assumed to be smaller), which means the cratons pre-date the collision. But Venus kept all its crust, hence it is too thick and the heat cannot get out.

StarDreamer · 2007-06-09 23:15:48

Jovian worlds formed coeval moons because their planetary disks were not disrupted by our evolving star. If they had been close enough to our star for the star to either steal or blow away their gas, then they would also have been close enough for the outer margins of their disks to be disrupted, collapsed (compressed prematurely) or whatever. My instinct says that L1 to the star so compresses the safety zone around the young planet that the gap from L1 to its Roche Limit is too poor in materials for a moon to evolve. Distant planets have more generous L1 points.

Also -- consider the element-balance of the Jovian system from moon to moon -- Io with all the sulphur is innermost (Venus), then Europa with all the water (Earth), then Callisto and Ganymede where independent magnetic fields begin to assert themselves.

nickname · 2007-06-10 06:54:30

Difficult to make any assumptions about 1 example of a solar system on how things end up how they do.

If we try to create patterns from what we see other than very general ones, we are sure to see whatever we want.

Everything we see in our solar system might be no more than just chance impacts location etc.

Spin rates can come down to just having more material hit one side of a planet, or huge impacts that alter tilt and change rotation completely.

If we look around our solar system at all the objects they seem to follow no real pattern of spin or position.

The early solar system must have been a very violent place for such variety to be made.

A thicker Venus hot crust would explain a lot about the Venus we see today.
Water could never form on the surface, it started with as much or more water than Earth but the surface mechanics of Venus never allowed the carbon to be locked away.

The water vapor cloud bank just slowly departed further and further from the surface as it got hotter, this also got the clouds closer to the powerful UV to accelerate the process, free 02 and carbon became C02 and hydrogen leaked to space.

If we start with Earthly amounts of Water and Carbon we get pretty much what Venus is today.

Spatula · 2007-06-10 15:08:06

I doubt this. Terrestrial rocky planets tend not to grow coeval moons, while the gas giants do with some uniformity. Mars has only 2 tiny captured asteroids. Mercury and Venus have nothing. Then Earth has this whopping big moon -- clearly an extraordinary situation demanding an extraordinary explanation.

Earth's hill sphere extends 1500 thousand km from the planet's center. That's a lot of room for a moon. Ours is only in the first 25% of it. Mars and Venus only have moderately smaller regions to form moons. There's no reason Venus couldn't hold an impact-formed moon, so your argument that it never had one would have to rely on finding a simpler, more likely explanation for its current rotational velocity.

The water vapor cloud bank just slowly departed further and further from the surface as it got hotter, this also got the clouds closer to the powerful UV to accelerate the process, free 02 and carbon became C02 and hydrogen leaked to space.
If we start with Earthly amounts of Water and Carbon we get pretty much what Venus is today.

I'm still going to disagree with this. If there were ever a significant amount of water on Venus, there should be a significant amount of molecular oxygen, yet there is none. The current CO2 is exactly the amount it should have. SO2 is a similar case. The complete lack of any oxygen on the planet does not lend itself to a large deposits of water that were lost to hydrogen photodisassociation. The Jovian moons have oxygen to show for this process. Earth has oxygen to show for this. Where is it on Venus?

It was never there. And that fits. The sun's early heat cleared it from that part of the solar system. For the same reason that Mercury is rich in high-density materials, and only received water from cometary impacts over billions of years, Venus should be much poorer in water than Earth.

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Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

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Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

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Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

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Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

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Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#81 2007-06-08 11:51:23

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#82 2007-06-08 12:31:53

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#83 2007-06-08 14:57:32

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#84 2007-06-08 16:53:46

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#85 2007-06-08 17:45:58

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#86 2007-06-08 19:58:11

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#87 2007-06-08 23:41:24

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#88 2007-06-09 01:45:08

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#89 2007-06-09 04:06:48

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#90 2007-06-09 10:48:02

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#91 2007-06-09 14:51:37

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#92 2007-06-09 16:30:32

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#93 2007-06-09 22:15:29

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#94 2007-06-09 22:19:30

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#95 2007-06-09 22:31:54

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#96 2007-06-09 22:54:20

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#97 2007-06-09 23:10:04

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#98 2007-06-09 23:15:48

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#99 2007-06-10 06:54:30

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

#100 2007-06-10 15:08:06

Re: Floating Venusian cities or Venus vs Mars vs Titan revisited

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