Which planet in this solar system would be most appropriate to terraform?

[Gliese123]

I've been reading about terraforming and really stuck with it. Which planet /moon has the most convenient conditions, such as mass, magnetic field, gravity, intensity of sunlight for possible terraform. Venus, Moon or Mars or some else? Which one do you think? And would it be possible?

Basic gravity conditions (which decides the ability to remain a atmosphere also all bodies are without considerable magnetic field):
Venus: 8.87 m/s²
Moon: 1.622 m/s²
Mars: 3.711 m/s²

 

[qraal]

I've been reading about terraforming and really stuck with it. Which planet /moon has the most convenient conditions, such as mass, magnetic field, gravity, intensity of sunlight for possible terraform. Venus, Moon or Mars or some else? Which one do you think? And would it be possible?

Basic gravity conditions (which decides the ability to remain a atmosphere also all bodies are without considerable magnetic field):
Venus: 8.87 m/s²
Moon: 1.622 m/s²
Mars: 3.711 m/s²

They were arguing this in General Engineering, but from an astronomical point of view I would claim that Venus was easier. But it depends on which bit of a planet is the most important. Venus has the most similar gravity to Earth and more than enough air. It does lack water, but that might not be such a big impediment, if some water can be supplied - a desert planet is more stable against runaway greenhouse at high insolation levels than a wet one. The chief problem is what one does with all the excess atmosphere. In theory the atmosphere should undergo collapse if the insolation reaching the surface can be reduced. If the upper atmosphere can either absorb the light that gets through to the ground at present or reflect it, then gradual atmospheric collapse should occur. But gradual. It'll probably take centuries for it cool and react with the soil, eventually forming carbonates, which is what the current atmosphere is believed to have been decomposed from millions of years ago.

Both Mars and the Moon need too much air to be added, and Mars needs more energy input, to really be front-runners. I know that's not what's generally assumed, but the logistics of supplying extra volatiles to either, and energy to Mars, is quite extraordinary.

So that's my opinion, astronomically/planetologically speaking.

 

[meWyatt]

I would think that Earth would be the place to start. If we cannot maintain its stability as a place congenial to human and most other existing life, then why would we allow such experimentation elsewhere? On the other hand, we've already done one significant experiment. Given enough gasoline and people driving cars, coal burning, mining and cow farts, we know we can bootstrap a process of warming on Mars. Can we survive on Earth long enough to reap the benefits? Probably not if at the same time we we are building that highway to Mars.

 

[PSLock]

Yes Venus would be the best bet in the inner solar system although I'm not sure how to speed up its rotational speed as would be needed to hopefully create an electromagnetic field as well as protect it from atmospheric collapse.
In the outer solar system Titan around Saturn is by far the best bet chemically as it is almost identical to Earth 4.5 billion years ago. But if you were able to construct some type of barrier around IO to collect the charged particles stripped off of it by Jupiter to hopefully lower the ambient radiation levels around Jupiter system and to generate energy, Europe or Ganymede, or even possible Callisto could make great locations. At least that's my 2 cents. hope you like.

 

[Gliese123]

Titan is a really cool moon. It would probably be a candidate for such terraform. Still, it has no magnetic field and barely massive enough to hold an atmosphere for to long. I've read somewhere that it loses big amounts of its atmosphere every day. Why is it so? Does Jupiter tear it apart? Sadly, the moons in this solar system has to little mass I assume. Venus for sure. It would probably be mainly a desert planet then, right?

 

[Gliese123]

They were arguing this in General Engineering, but from an astronomical point of view I would claim that Venus was easier. But it depends on which bit of a planet is the most important. Venus has the most similar gravity to Earth and more than enough air. It does lack water, but that might not be such a big impediment, if some water can be supplied - a desert planet is more stable against runaway greenhouse at high insolation levels than a wet one. The chief problem is what one does with all the excess atmosphere. In theory the atmosphere should undergo collapse if the insolation reaching the surface can be reduced. If the upper atmosphere can either absorb the light that gets through to the ground at present or reflect it, then gradual atmospheric collapse should occur. But gradual. It'll probably take centuries for it cool and react with the soil, eventually forming carbonates, which is what the current atmosphere is believed to have been decomposed from millions of years ago.

Both Mars and the Moon need too much air to be added, and Mars needs more energy input, to really be front-runners. I know that's not what's generally assumed, but the logistics of supplying extra volatiles to either, and energy to Mars, is quite extraordinary.

So that's my opinion, astronomically/planetologically speaking.

I guess- lack of mass and magnetic field= hard to do something.

 

[Gliese123]

I would think that Earth would be the place to start. If we cannot maintain its stability as a place congenial to human and most other existing life, then why would we allow such experimentation elsewhere? On the other hand, we've already done one significant experiment. Given enough gasoline and people driving cars, coal burning, mining and cow farts, we know we can bootstrap a process of warming on Mars. Can we survive on Earth long enough to reap the benefits? Probably not if at the same time we we are building that highway to Mars.

Highway to Mars wouldn't be so bad? :D You're right, Earth need to be taken care of. And as soon as there are so much people living on this poor planet. I guess countries has to stop compete about the planet's resources and start to cooperate. But it's to much conflicts for that bright thought to come true I suppose...

 

[Gliese123]

They were arguing this in General Engineering, but from an astronomical point of view I would claim that Venus was easier. But it depends on which bit of a planet is the most important. Venus has the most similar gravity to Earth and more than enough air. It does lack water, but that might not be such a big impediment, if some water can be supplied - a desert planet is more stable against runaway greenhouse at high insolation levels than a wet one. The chief problem is what one does with all the excess atmosphere. In theory the atmosphere should undergo collapse if the insolation reaching the surface can be reduced. If the upper atmosphere can either absorb the light that gets through to the ground at present or reflect it, then gradual atmospheric collapse should occur. But gradual. It'll probably take centuries for it cool and react with the soil, eventually forming carbonates, which is what the current atmosphere is believed to have been decomposed from millions of years ago.

Both Mars and the Moon need too much air to be added, and Mars needs more energy input, to really be front-runners. I know that's not what's generally assumed, but the logistics of supplying extra volatiles to either, and energy to Mars, is quite extraordinary.

So that's my opinion, astronomically/planetologically speaking.

Also, thank you for your informative facts :)

 

[2milehi]

Titan is a really cool moon. It would probably be a candidate for such terraform. Still, it has no magnetic field and barely massive enough to hold an atmosphere for to long. I've read somewhere that it loses big amounts of its atmosphere every day. Why is it so? Does Jupiter tear it apart? Sadly, the moons in this solar system has to little mass I assume. Venus for sure. It would probably be mainly a desert planet then, right?

Titan orbits Saturn

 

[qraal]

Titan is a really cool moon. It would probably be a candidate for such terraform. Still, it has no magnetic field and barely massive enough to hold an atmosphere for to long. I've read somewhere that it loses big amounts of its atmosphere every day. Why is it so? Does Jupiter tear it apart? Sadly, the moons in this solar system has to little mass I assume. Venus for sure. It would probably be mainly a desert planet then, right?

Titan's gravity is pretty low and the top of the atmosphere needs to stay cool or else it will escape. Some hydrogen does escape even now, but heavier gases should be retained if the upper levels can stay cool. As for magnetic fields, the solar wind is 100 times weaker than at Earth's orbit, so there's no erosion issues.

 

[eachus]

There are low-lying areas on Mars which could be cheaply terraformed, for example the Hellas Basin is about 10 miles lower than the surrounding highlands. Rather than trying to contain the atmosphere, you could create "blankets" filled with hydrogen and made of thin polymer, that were say a square kilometer each. Some hydrogen would escape, but much less than without the covers. Make them reflective only at night, and you would soon have termperatures above freezing in the valley.

Repeat for other large valleys and eventually you have more habitable land than on Earth.

On Venus, there is another choice. Build large enclosed structures containing an atmosphere like that of Earth. It will have significant positive lift at altitudes which are at Earth normal pressure and temperature. The problem is the super-rotation of the atmosphere. It rotates around the planet in less than a week, while a day is close to or identical to a local year. This means your areostat is going to need to be big, and sturdy, and fabricated somewhere other than on Venus.

But if you want to think big, what you do is this. Go to Saturn, throw large lumps of ice from the rings at Venus. Aiming carefully, you can get the planet's rotation up to a day or so. While you are at it, do the polymer blanket trick, but black at night, reflective by day. Eventually you get a big rain, with sulfurous and carbonic acids filling the lowlands and making them seas. How do you get rid of all that acid? Some will react with the rocks, forming water, but you need to get rid of quite a bit more than that. There is enough nitrogen already for an atmosphere, but you need to use sunlight to split some of the acids into H2O (water) sulfur, carbon and oxygen. You could combine the sulfur and carbon to form CS2 which is nasty stuff, but better would be to make big piles of sulfur and carbon (coal).

You could also form caverns inside Earth's moon, and that will probably be done at some point. But living at less than about Mars gravity will result in adverse health effects, so Mars or Venus is better for long time habitation.

Oh, and don't forget about Mercury. There are areas near the poles that should be habitable (for humans).

 

[qraal]

There are low-lying areas on Mars which could be cheaply terraformed, for example the Hellas Basin is about 10 miles lower than the surrounding highlands. Rather than trying to contain the atmosphere, you could create "blankets" filled with hydrogen and made of thin polymer, that were say a square kilometer each. Some hydrogen would escape, but much less than without the covers. Make them reflective only at night, and you would soon have termperatures above freezing in the valley.

Repeat for other large valleys and eventually you have more habitable land than on Earth.

Nice. A Hellas dome/cover would be quite an amazing piece of architecture.

On Venus, there is another choice. Build large enclosed structures containing an atmosphere like that of Earth. It will have significant positive lift at altitudes which are at Earth normal pressure and temperature. The problem is the super-rotation of the atmosphere. It rotates around the planet in less than a week, while a day is close to or identical to a local year. This means your areostat is going to need to be big, and sturdy, and fabricated somewhere other than on Venus.

Aerostat colonies are a precondition of any Terraforming effort I would think, else one has to wait a long time for real estate.

But if you want to think big, what you do is this. Go to Saturn, throw large lumps of ice from the rings at Venus. Aiming carefully, you can get the planet's rotation up to a day or so.

Not physically feasible I'm afraid. The energy required would need very large masses of ice striking the planet, which I doubt would impress the people in the aerostats.

While you are at it, do the polymer blanket trick, but black at night, reflective by day. Eventually you get a big rain, with sulfurous and carbonic acids filling the lowlands and making them seas.

The amount of H2SO4 isn't very high, a few centimeters at most. And "carbonic acid" - carbon dioxide dissolved in water - needs a lot of water. Depending on the porosity of the regolith, most of the condensed water/carbon dioxide could end up soaked into the ground, rapidly combining with the salts there to make carbonate.

But condensing the atmosphere seems a good start to changing Venus. Importing water, though, might be unnecessary if we can import hydrogen instead and react it with the CO2 via the Bosch reaction. However the amount of carbon generated might have issues. If we could convert carbon dioxide directly into amorphous carbonia, then the job might be easier. I am unsure if the stuff is metastable enough at low pressures to be interesting, though if it could be confined inside buckyballs and nanotubes, then we're talking. The pressures inside such molecular cages can be thousands of bars, enough perhaps for stable carbonia at STP. Making buckyballs and nanotubes from carbon dioxide, of course, leaves free oxygen.

Any clever physical chemists on this board?

Oh, and don't forget about Mercury. There are areas near the poles that should be habitable (for humans).

Sort of. The ground is cool, but the Sun is still hot. And making Mercury retain an atmosphere so close to the Sun would be quite a trick. MESSENGER should hopefully tell us more about the volatiles available near the Hermean poles.

 

[eachus]

Nice. A Hellas dome/cover would be quite an amazing piece of architecture.

I was trying to describe a solution that doesn't require a one-piece dome. You make "blankets" of thin polymer with pockets full of hydrogen. If you use electrolysis to make oxygen, you release both H2 and O2. The blankets float on the H2/O2 interface in the atmosphere, and both reduce the mixing (which is a good thing ;-) and allows the hydrogen to escape. Technically some will escape completely from the atmosphere, but most will end up over some other part of Mars, and reacting with the CO2 or the iron oxide on the ground, eventually ending up as water in the (Martian) atmosphere. Recycle as above.

At some point you do have a complete dome over Hellas, with several thicknesses of blankets, but no significant pressure difference. Since Hellas is plenty deep, the pressure at ground level could reach Earth levels. Of course, the first goal would be around 6 pounds of pressure with 50% O2. From that point on you want to add mostly nitrogen or inert gasses.

Aerostat colonies are a precondition of any Terraforming effort I would think, else one has to wait a long time for real estate...

Not physically feasible I'm afraid. The energy required would need very large masses of ice striking the planet, which I doubt would impress the people in the aerostats.

Glad I had finished drinking my tea when I read this--I would have needed to clean my keyboard. ;-)

Obviously the two approaches are mutually exclusive or need to be correctly coordinated. Who knows, maybe you could sell living space in the areostats with bonus fireworks displays daily and special effects. ;-)

The use of tethers reduces the required energy input at the Saturn end. The ice will melt in transit, and if you first wrap the ice in plastic, the energy will be dissipated high in the atmosphere. Of course, the coupling between the atmosphere and the planet doesn't seem to be all that great today. So maybe you want to use sunshades or wrappers reflective on the sunward side to get supercooled ice bombs.

The necessary angular momentum is not an issue--assuming you can do the rest of it. If you are going to move 3% of the mass of Venus from Saturn's rings the rest is detail. (And probably tree-hugger lawsuits to prevent "destruction" of the rings.)

The amount of H2SO4 isn't very high, a few centimeters at most. And "carbonic acid" - carbon dioxide dissolved in water - needs a lot of water. Depending on the porosity of the regolith, most of the condensed water/carbon dioxide could end up soaked into the ground, rapidly combining with the salts there to make carbonate.

Actually latest reports show more SO2 than H2SO4. A detail unless the reaction with rocks sops up all that precious oxygen you are making. As for the excess carbon from using CO2 as an oxygen source--both for free oxygen and water--make it into diamonds or diamonoid for construction materials. Waste not, want not. ;-)

Sort of. The ground is cool, but the Sun is still hot. And making Mercury retain an atmosphere so close to the Sun would be quite a trick. MESSENGER should hopefully tell us more about the volatiles available near the Hermean poles.

I'm assuming a (partially) reflective dome. You want to let through about the same amount of sunlight as at the Earth's surface. If you want more than say, one hundred square kilometers for growing things, try some other planet, or the moon.

Note that once we build a space elevator at Earth, projects on this scale seem a lot more feasible. Any day now some company is going to start selling a (single multi-walled) cheese slicer.* Then building a space elevator will just be engineering.

* Of course, in today's litigious society, the cheese slicer may never make it to the stores. Yes, it will be much less dangerous than the kitchen knives on the next shelf,... Eventually you will need a weapons permit for those knives, and the cheese slicer too. That's why it is time to leave Earth.

 

[Chronos]

Introducing an atmosphere would be a huge engineering [and energy intensive] challenge. Venting some of the atmosphere from venus seems much more practical - and offers a potentially useful energy source for other teraforming activities.

 

[qraal]

Introducing an atmosphere would be a huge engineering [and energy intensive] challenge. Venting some of the atmosphere from venus seems much more practical - and offers a potentially useful energy source for other teraforming activities.

We're on a physics board and you're making that claim? It's the silliest truism that has floated around discussions like this for years. Quantify it and see if it is true. Escape energy from Venus is 54 MJ/kg. Adding enough hydrogen to convert the carbon dioxide into water and carbon needs four hydrogen atoms for every pair of oxygens in the CO2. Thus 1/11 the mass of CO2 in hydrogen needs to be imported from a gas giant. Uranus has the lowest escape energy per unit mass which, after correcting for its rotation, is 173 MJ/kg and not much extra for a minimum energy transfer to Venus. About 200 MJ/kg - but remember we only need 1/11 the mass of carbon dioxide in hydrogen - thus just 22 MJ/kg for sufficient hydrogen delivery to Venus to convert its atmosphere.

Thus throwing away 4.6E+20 kg of atmosphere is totally unnecessary by better than a factor of 2 - yet it gets trotted out every time this discussion comes up! And on a Physics board!

 

[Chronos]

We're on a physics board and you're making that claim? It's the silliest truism that has floated around discussions like this for years. Quantify it and see if it is true. Escape energy from Venus is 54 MJ/kg. Adding enough hydrogen to convert the carbon dioxide into water and carbon needs four hydrogen atoms for every pair of oxygens in the CO2. Thus 1/11 the mass of CO2 in hydrogen needs to be imported from a gas giant. Uranus has the lowest escape energy per unit mass which, after correcting for its rotation, is 173 MJ/kg and not much extra for a minimum energy transfer to Venus. About 200 MJ/kg - but remember we only need 1/11 the mass of carbon dioxide in hydrogen - thus just 22 MJ/kg for sufficient hydrogen delivery to Venus to convert its atmosphere.

Thus throwing away 4.6E+20 kg of atmosphere is totally unnecessary by better than a factor of 2 - yet it gets trotted out every time this discussion comes up! And on a Physics board!

Within the context of what WAS said, utilization of the excess atmospheric mass was clearly intended. My unfortunate use of the term 'venting' obviously derailed the point - it is more efficient to make use of what is already present while minimizing import of what is not. Liquid CO2 can be combined with Hydrogen in a pressurized reactor to produce Carbon, Oxygen, and Water: 2H+CO2 = C+O+H2O. This reaction also occurs when CO2 is sequestered underground on earth. Over tine, the CO2 combines naturally with hydrogen in the rocks. Of course, it is unknown if venusian rocks contain enough hydrogen for sequesterization to be effective on a planetary scale. A substantial quantity of hydrogen would probably need to be imported.

 

[qraal]

Within the context of what WAS said, utilization of the excess atmospheric mass was clearly intended. My unfortunate use of the term 'venting' obviously derailed the point - it is more efficient to make use of what is already present while minimizing import of what is not. Liquid CO2 can be combined with Hydrogen in a pressurized reactor to produce Carbon, Oxygen, and Water: 2H+CO2 = C+O+H2O. This reaction also occurs when CO2 is sequestered underground on earth. Over tine, the CO2 combines naturally with hydrogen in the rocks. Of course, it is unknown if venusian rocks contain enough hydrogen for sequesterization to be effective on a planetary scale. A substantial quantity of hydrogen would probably need to be imported.

Well I agree in that sense of what you said. What about reacting the CO2 with oxides to make carbonates?

 

[Chronos]

That is a very good option. Utilizing acidic compounds already present in the venusian atmosphere [in particular sulfuric acid] is a practical option as well. Local resources should be utilized to the maximum extent possible in any teraforming effort. Venus has an abundance of raw materials making it a promising teraforming candidate, IMO. Some of the gas giant moons are also promising candidates for teraforming due, in part, to their proximity to virtually unlimited additional material resources. The main disadvantage is their severe solar energy deficiency.

 

[Gliese123]

Titan orbits Saturn

Sorry. I was nagging about Jupiter's moons in another replay while writing something about Titan. Lol.. Ofc it orbits Saturn..

 

[Gliese123]

There are low-lying areas on Mars which could be cheaply terraformed, for example the Hellas Basin is about 10 miles lower than the surrounding highlands. Rather than trying to contain the atmosphere, you could create "blankets" filled with hydrogen and made of thin polymer, that were say a square kilometer each. Some hydrogen would escape, but much less than without the covers. Make them reflective only at night, and you would soon have termperatures above freezing in the valley.

Repeat for other large valleys and eventually you have more habitable land than on Earth.

On Venus, there is another choice. Build large enclosed structures containing an atmosphere like that of Earth. It will have significant positive lift at altitudes which are at Earth normal pressure and temperature. The problem is the super-rotation of the atmosphere. It rotates around the planet in less than a week, while a day is close to or identical to a local year. This means your areostat is going to need to be big, and sturdy, and fabricated somewhere other than on Venus.

But if you want to think big, what you do is this. Go to Saturn, throw large lumps of ice from the rings at Venus. Aiming carefully, you can get the planet's rotation up to a day or so. While you are at it, do the polymer blanket trick, but black at night, reflective by day. Eventually you get a big rain, with sulfurous and carbonic acids filling the lowlands and making them seas. How do you get rid of all that acid? Some will react with the rocks, forming water, but you need to get rid of quite a bit more than that. There is enough nitrogen already for an atmosphere, but you need to use sunlight to split some of the acids into H2O (water) sulfur, carbon and oxygen. You could combine the sulfur and carbon to form CS2 which is nasty stuff, but better would be to make big piles of sulfur and carbon (coal).

You could also form caverns inside Earth's moon, and that will probably be done at some point. But living at less than about Mars gravity will result in adverse health effects, so Mars or Venus is better for long time habitation.

Oh, and don't forget about Mercury. There are areas near the poles that should be habitable (for humans).

Thank you a lot for your informative knowledge. Isn't it easier to create an atmophere than remove it? Mars feels like the a good choice. If the surface eventually heat up, gases, (such as nitrogen and most of all CO₂) will heat it up an be released for a heating process.

 

[Chronos]

Converting excess atmosphere would be the more practical approach. In the case of venus, there are several ways to create fuel, water, oxygen and other usable byproducts from C02. Given the great abundance of raw materials and solar energy, the project could conceivably be self supporting. C02 sequestration is a relatively cheap way to get started and would provide some water and oxygen. Assuming you could economically import hydrogen [possibly from the gas giants], C02 reactors could be deployed. Once an adequate supply of water was accumulated, plant life could be introduced. The teraforming process would then be limited only by the availability of water. Perhaps there are sufficient ice reserves in the asteroid belt to suppment the water supply.

 

[siiix]

here is a radical idea.. one of Mars moons Phobos has large concentration of watter... why not just crash that thing into Mars creating so not just a huge supply of watter but i would assume such impact would temporary generate large amounts of heat, there for temporary evaporative part of the watter and create temporary an atmosphere that its easier to work with

with our current technology crashing such size moon's orbit should be possible

 

[qraal]

here is a radical idea.. one of Mars moons Phobos has large concentration of watter... why not just crash that thing into Mars creating so not just a huge supply of watter but i would assume such impact would temporary generate large amounts of heat, there for temporary evaporative part of the watter and create temporary an atmosphere that its easier to work with

with our current technology crashing such size moon's orbit should be possible

Hi siiix,
Phobos was long thought to be a carbonaceous chondrite, but current thought is that its density is low due to a high porosity and the actual water content is quite low.

 

[TMEubanks]

I would vote for Venus. Put a Sunshade at the Sun-Venus L1 Lagrange Point (about 100 kilotons of metal should do), and cool the surface down to something reasonable. Once that happens, turn the Sun partially back on and introduce biology (plants) to turn Carbon Dioxide into surface material. Once the surface pressure is lowered to order (1 bar), you no longer need the Sun shade at all. By that time, there should be a lot of Oxygen in the atmosphere, and you should be able to walk around without protection.

Venus has enough Hydrogen to form a layer of water about 50 meters thick if the surface were smooth, which wouldn't give you an Earth type global ocean, but is enough for quite a few "Great Lakes," and even a Mediterranean or two.

(It would be much tougher to spin the planet up - a km sized asteroid would hardly change either the spin rate or the total amount of surface water, and I don't see us moving much bigger ice chunks around anytime soon.)

I have run some numbers on this, and think it would take 100-500 years, a long time by our standards, but not long compared to the benefit of having a new planet to live on.

 

[Cosmo Novice]

I would vote for Venus. Put a Sunshade at the Sun-Venus L1 Lagrange Point (about 100 kilotons of metal should do), and cool the surface down to something reasonable. Once that happens, turn the Sun partially back on and introduce biology (plants) to turn Carbon Dioxide into surface material. Once the surface pressure is lowered to order (1 bar), you no longer need the Sun shade at all. By that time, there should be a lot of Oxygen in the atmosphere, and you should be able to walk around without protection.

Venus has enough Hydrogen to form a layer of water about 50 meters thick if the surface were smooth, which wouldn't give you an Earth type global ocean, but is enough for quite a few "Great Lakes," and even a Mediterranean or two.

(It would be much tougher to spin the planet up - a km sized asteroid would hardly change either the spin rate or the total amount of surface water, and I don't see us moving much bigger ice chunks around anytime soon.)

I have run some numbers on this, and think it would take 100-500 years, a long time by our standards, but not long compared to the benefit of having a new planet to live on.

I would love to see your numbers on this. Does this 100-500 years take into account development of all the necessary technology required for this endeavour? I find the timescales you are talking about a little absurd. We cannot just drop plants onto a Venusian atmosphere - we would need to develop an ecology to be able to survive in the Venusian environment. We do not understand Earth ecology fully and I doubt 100-500 years is anything like a reasonable timeframe.

 

[vemvare]

Titan is not at all similar to Earth 4.5 billion years ago.

Basically, Titan is a kupier-belt object captured by Saturn, at least a third of its mass is water, and its reducing nitrogen atmosphere is also comparatively massive. Earth is a terrestrial planet who happened be of just the right size and composition to end up on the fine line between a greenhouse runaway and a snowball, thanks to its magnetic field and being hit by just the right amount of cometary debris in the LHB.

Venus is so close to the sun it is probably impossible to maintain an Earth-like biosphere. Franky, though, I have no idea what effect would dominate at an insolation of roughly 2x that of the Earth, either clouds raising the albedo or water vapor acting as a greenhouse gas. As other have said, to maintain a reasonable temperature, it is probably necessary to block most of the sunlight.

Chemically, Venus has far too much carbon dioxide and far too little water. Importing hydrogen and chemically converting the CO₂ into carbon and water could work, but storing C as terra preta or under the oceans can only go so far, after all it is 230 tons per square meter. Forget storing it as hydrocarbons, that amount would be order of magnitude above what can be found on the Earth. The problem with carbon of course is that it is combustible, but if it is stored as SiC, it could be considered safe, though this would mean that twice the amount of hydrogen would be needed, or ~151 tons per square meter, to take care of the O₂ liberated from SiO2.

According to my chemistry book (doing a course atm), at a CO₂ partial pressure of almost 93 bar and a temperature of 735K, K for most reactions like CaO + CO₂ ---> CaCO₃ favors products, in other words carbonates would not decompose. Hence, one can conclude that the lithosphere of Venus isn't likely to be full of alkaline oxides longing to form carbonates, rather, it is full of carbonates. Correct me if I'm wrong, but if the atmosphere is cooled down, the sulfuric acid (which isn't at all as much as people tend to think) would be gone very rapidly.

Oh, BTW, 151 tons of H₂ per square meter equals 6.95*10¹⁹ kilograms.

The volatile content of the upper layers of Mars is not known, though it is likely to be quite high. One could liberate these volatiles by using a massive Fresnel-lens/mirror in conjunction to simply burn them out. This would of course be far simpler than moving petatons of matter across the solar system, but the big question is how much nitrogen such an atmosphere would contain (mainly from abiogenic nitrates). Estimates vary by orders of magnitude! To give Mars an Earth like atmosphere with an N₂ partial pressure of 0.78 bar, 20.6 tons per square meter would be needed, or 3*10¹⁸ kilograms. There have been speculation, though, that CO₂ instead of N₂ could serve as a similar "inert blanket gas" for a modified biosphere, IIRC the old Newmars forum had a lot of good posts on that.

--

Terraforming is of course extremely speculative. A "terraforming future" isn't a future with a couple of thousand NASA/ISA scientist-astronauts flying around the solar system, it is a future where millions of people live their lives in massive space stations, where thousands of people leave and return to Earth each day, and where asteroids are moved around, smashed to pieces and mined! As such, it is likely to be distant future, which of course means that huge advances will be made in science, so much of what we're speculating about here will be laughably wrong if read by the generation that actually start the terraforming process.

 

[Ryan_m_b]

I would vote for Venus. Put a Sunshade at the Sun-Venus L1 Lagrange Point (about 100 kilotons of metal should do), and cool the surface down to something reasonable. Once that happens, turn the Sun partially back on and introduce biology (plants) to turn Carbon Dioxide into surface material. Once the surface pressure is lowered to order (1 bar), you no longer need the Sun shade at all. By that time, there should be a lot of Oxygen in the atmosphere, and you should be able to walk around without protection.

Venus has enough Hydrogen to form a layer of water about 50 meters thick if the surface were smooth, which wouldn't give you an Earth type global ocean, but is enough for quite a few "Great Lakes," and even a Mediterranean or two.

(It would be much tougher to spin the planet up - a km sized asteroid would hardly change either the spin rate or the total amount of surface water, and I don't see us moving much bigger ice chunks around anytime soon.)

I have run some numbers on this, and think it would take 100-500 years, a long time by our standards, but not long compared to the benefit of having a new planet to live on.

I too am highly skeptical of your claims. What exactly do you propose to do with 160 kilotonnes of metal? I assume you mean create a huge disk to block out the sun but it isn't stated. Related to this the average surface temperature is nearly 500^oC and the atmosphere is almost entirely insulating carbon dioxide. How long do you think it would take to radiate all that heat? And how are you going to deal with being closer to the sun when the shade comes down?

Regarding the carbon dioxide, there is around 450 million billion tonnes in the atmosphere of Venus! That's around 1,000 tonnes per square metre. There's no way you can just drop plants and expect all that to be locked up in biomass. In addition where are you going to get all the nitrogen from? How are you going to get rid of all the sulfur, argon etc?

On the subject of the ecology as has been said you can't just drop a few seeds and expect the amazon. Organisms rely heavily on other organisms and the right environmental conditions. Without the appropriate soil biota (bacteria, worms etc), fungi, pollinators etc nothing is going to grow. On top of that there are the problems of pressure, day light length etc. It may be possible one day to map out self-sufficient and productive ecological webs but you would have to somehow breed them for Venusian conditions which would be a nightmare and an incredibly long process.

 

[siiix]

I too am highly skeptical of your claims. What exactly do you propose to do with 160 kilotonnes of metal? I assume you mean create a huge disk to block out the sun but it isn't stated. Related to this the average surface temperature is nearly 500^oC and the atmosphere is almost entirely insulating carbon dioxide. How long do you think it would take to radiate all that heat? And how are you going to deal with being closer to the sun when the shade comes down?

Regarding the carbon dioxide, there is around 450 million billion tonnes in the atmosphere of Venus! That's around 1,000 tonnes per square metre. There's no way you can just drop plants and expect all that to be locked up in biomass. In addition where are you going to get all the nitrogen from? How are you going to get rid of all the sulfur, argon etc?

On the subject of the ecology as has been said you can't just drop a few seeds and expect the amazon. Organisms rely heavily on other organisms and the right environmental conditions. Without the appropriate soil biota (bacteria, worms etc), fungi, pollinators etc nothing is going to grow. On top of that there are the problems of pressure, day light length etc. It may be possible one day to map out self-sufficient and productive ecological webs but you would have to somehow breed them for Venusian conditions which would be a nightmare and an incredibly long process.

the heat would radiate probably in days or weeks, that's not the problem, the problem is that the position of the sun and planet are not constant, the "disk" would be constantly have to be positioned , it would be pretty much a space ship

also I'm not convinced that a 160 mile disk would do the trick, this would need to be calculated, i assume the sun looks larger from there too ... with that said it is possible , but not a small task, also the "disk" don't have to be metal, it can me any material that can with stand those conditions, a sun light reflecting surface would probably be the best

 

[chill_factor]

heat transfer by radiation is incredibly slow and inefficient for something of planet size. what makes it so inefficient is because planets are not blackbodies; the heat they radiate from the surface will induce convection currents in the atmosphere which bring almost all of it straight back down. in addition, clouds will also reflect radiation back to the surface, and the amount of reflectivity towards incoming solar radiation is unimportant; Venus is already one of the brightest and most reflective objects in the solar system.

 

[JonDE]

the heat would radiate probably in days or weeks, that's not the problem, the problem is that the position of the sun and planet are not constant, the "disk" would be constantly have to be positioned , it would be pretty much a space ship

also I'm not convinced that a 160 mile disk would do the trick, this would need to be calculated, i assume the sun looks larger from there too ... with that said it is possible , but not a small task, also the "disk" don't have to be metal, it can me any material that can with stand those conditions, a sun light reflecting surface would probably be the best

I'm not sure where you got the 160 mile disk number, apparently you and Ryan are speed reading. The original poster said 100 kilotonnes, but I understand where you are coming from. Obviously if u wanted to completely shade the entire planet at once (to drop the temperature quickly) the object would have to have a greater diameter then the planet itself. It of course doesn't need to be that big if we are a little more patient. Unfortunetly the post was a little light on most details so it is hard to refute.