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In my setting, Venus is still very much still hostile to a normal human without equipment, but isn't hot enough to melt lead and has a relatively low pressure compared to now.

How could this potentially be achieved? The more grounded in science and modern technology, the better.

Rough numbers; pH of the air is roughly 5.7, surface temperature is around 120 degrees Fahrenheit (50 degrees Celsius). Pressure is around 2.3 bars.

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  • $\begingroup$ When you want something man could explore in an EVA or deep-sea diving suit, why would you stop there, please? Surely the difference between those suits and Earth-normal conditions is immense in itself, but doesn't it shrink beneath worrying about when compared to part-terraforming Venus in the first place? Assuming conditions for EVA and deep-sea diving suits are similar, how sure are you that once started, the 'partial' forming could be stopped at their level? $\endgroup$ Apr 8 at 19:27
  • $\begingroup$ the simplest way is just to strip off most of venus's atmosphere. that solves most of the problems with putting people on venus. you can find lots of stuff on terraforming venus what prior research have you done? $\endgroup$
    – John
    Apr 8 at 21:16
  • $\begingroup$ @SerbanTanasa since the OP is asking "low enough ph and cold enough to NOT kill a person instantly" something that kills in 30 seconds is already more than enough. Maybe it's the OP who needs to rethink their question. $\endgroup$
    – L.Dutch
    Apr 9 at 3:01
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    $\begingroup$ @Escapeddentalpatient. And what is pH of air? pH of airborne water droplets? $\endgroup$
    – Mithoron
    Apr 9 at 12:31
  • $\begingroup$ You're right, it's the wrong word, but I'm not enough of a chemist to know the right one. Corrosiveness/inertness perhaps. @Mithoron $\endgroup$ Apr 9 at 16:30

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Big parasol near L1.

Put a big (roughly Venus-sized) solar sail slightly sunward of the Venus-Sun L1 Lagrange point. By varying the size or reflectivity of the solar sail, we can slightly increase or decrease the radially outward thrust from solar wind. Gravity will tend us towards the Sun, away from the L1 point, for points radially inward towards the sun from the L1 point, so by balancing this with variable thrust from solar wind, we can stay balanced on the equilibrium.

Think about making a thin book stand up straight. If you try to keep it balanced exactly vertically, you need to push on it from both directions, or it will fall over. But if you let it tip slightly in one direction, and use your hand to apply a slight force in the opposite direction of the tip, it's easy to keep it standing up almost straight with just one direction of force. We have solar wind force that would be pushing our parasol out of equilibrium anyway, so putting our parasol sunward of L1 solves one problem with the other problem!

Gravity will tend us towards the L1 point in the polar and azimuthal directions if we move away from the L1 point in those directions. We can help this by trimming the direction of the reflection, and hence the direction of the thrust from the solar wind (conserving momentum with the reflected light).

No sunlight reaching Venus = much colder Venus pretty soon. The atmosphere will precipitate out after a while, too.

This could be accomplished using modern technology, but not by modern humanity. The other barriers - required industrial capacity and resource availability - make this unachievable by any society which doesn't have an industrial base that compares to ours the way that our globally integrated 21st century industrial base compares to the industrial base of a single tribe of paleolithic hunter-gatherers.

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    $\begingroup$ I agree with this. The ~98% of the atmos that's CO2 being now snow would make the pressure drop dramatically. $\endgroup$ Apr 8 at 13:15
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    $\begingroup$ Kurzgesagt actually did a video on this a while ago $\endgroup$
    – Seggan
    Apr 8 at 15:11
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    $\begingroup$ Would it really precipitate? For CO2 ice you need way lower temperature than what OP proposes... and what suits humans. $\endgroup$
    – Mithoron
    Apr 9 at 12:34
  • $\begingroup$ @Mithoron rain is also called precipitation , so we'd only need to achieve liquidity temperatures. $\endgroup$
    – Hobbamok
    Apr 9 at 14:13
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    $\begingroup$ @Mithoron i think they mean CO2 rain, not water rain. According to this phase diagram I found, CO2 starts precipitating (at Venusian pressures) around 300 K, so a drop of ~430 K is needed. The greenhouse effect contributes ~470 K to Venus, so if you block the Sun it will eventually drop to the point where CO2 starts precipitating. $\endgroup$
    – Seggan
    Apr 9 at 16:03
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Vacuum tank technology has really been a godsend for Venusians. While hardened robotic excavation and mining operations are proceeding smoothly on the surface and provide plenty of raw materials for habitat construction, settling on the surface would require removing about an atmospheric mass equivalent to about 30% of Earth's Oceans, which is kind of a hassle to say the least.

Thankfully, thanks to the invention of floating vacuum tanks, we can create stable multimegaton floating structures about 50-55km up. At that height, the (mostly CO2) atmospheric pressure is about 1 (Earth) atmosphere (100k Pa) and the temperature a balmy 300K (80F). You obviously would die instantly if you breathed the local air, but you won't die of cold, heat, compression or decompression. The hardened transparent aerogel domes provide protection from the CO2 and acidic elements in the atmosphere for the habitations.

One thing to note is that the structure will necessarily be partaking in the upper atmospheric phenomenon known as super-rotation (i.e. moves around the planet at speeds upward of 350km/hr, which the weaklings back on Earth would find exceeds any category V hurricane). In order to conduct interplanetary exchanges, we rely on landing platforms above 70km, where the apparent wind force decreases to (an earth equivalent of) a light breeze. On the plus side, thanks to the sails carrying us around the planet, habitat apparent days are about 4 Earth-days long.

Even at that height, the upper atmospheric cloud cover would make the main habitats unable to see the sun or power reflectors, so we would tend to rely on nuclear (and wind) power for most of our needs.

One fun sport folks here engage in is to put on pressure suits and engage in low-atmospheric (40km high) barely-powered flight. You can basically flap mechanical wings and fly. It's a bit hot and the pressure is kinda high, and it's a bit, uh, acidic, so your mileage might vary. Locals love it tho.

temperature and pressuregas composition perceived wind speeds

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What technology levels are to be used to terraform it?

Without that information, we can pick some farily simple ideas, that do not require super-tech:

  • Using a solar umbrella to partially shield Venus from the Sun. This would cause the temperature to drop, chemical vapors to turn liquid and fall to the ground, and pressure would drop as well. The Umbrella would have to remain in place for eternity though, or Venus would heat right back up. Bonus: the umbrella could convert the solar energy into electromagnetic field, and use that to partially shield Venus from radiation as well.

  • use chemical reactions to bind Venusian atmosphere. There are plenty of cheap, but bulky chemicals that can be used here. Since Venusian atmosphere is acidic and rich in CO2, the easiest way to bind it is to use billions of tons of calcium oxide, basic lime (sodium hydroxide), and most importantly potash: potassium hydroxide. CaOH2, NaOH and KOH react strongly with CO2, forming chalky dust and water. All also react with acids, though this might release some of the captured CO2. So pretty much what you need is produce a lot of CaOH2, NaOH and KOH in space (out of K- type asteroids, somehow?), crush it to small bits, and "snow" it all over Venus. Bonus point: the alkaline "snow" will be chalky-white, and thus increase Venusian albedo, making it slightly cooler.

  • use rust to bind the acids in Venusian atmosphere. Same as the above, but this time we use the significantly much more common iron asteroids, ground to dust, and rained over Venus. Iron rust reacts with acid, creating largely harmless salts and water or hydrogen. The unfortunately small amount of hydrogen will either burn to water, if there is excess oxygen available, or float away to the topmost layer of the Venus atmosphere and become non-factor, so then we need the next step;.

  • finally, hydrogen bombardment. Bombarding Venus with HUGE amounts of hydrogen would convert its atmosphere into harmless water and bind CO2 into coal, in Bosch reaction. The problem is, you need to first do the previous steps (umbrella, chalk, rust,) to prepare Venus, otherwise the insane heat, pressure and radiation on Venus will just cause your hydrogen to get blasted back into space. Hydrogen extremely abundant, but hard to store, transport and use, and thus would be the slowest part of the whole process.

The final, by far the longest step would be to use the iron dropped on Venus, plus its abundant atmospheric energy to criss-cross the planet with electromagnetic rails, to give it some semblance of magnetosphere. Either that, or keep on producing bigger, and more redundant solar umbrellas so that Venus is always properly shielded from being baked with solar radiation.

As you wanted only to partially terraform Venus, the steps above should be enough. Once the pressure and heat on Venus is no longer utterly hellish, just extremely bad, it becomes a self-solving problem: all the chemical reactants, heat and pressure energy on Venus can be converted into useful energy for manufacturing, which you can use to build giant Venusian dirigibles to float in the safer parts of the atmosphere, dig underground bunkers, and build arcologies with 50 meter-thick reinforced walls to protect the humans there. On Earth, creating energy is costly. On Venus, energy is free and abundant, it is getting rid of it that is the problem.

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  1. You need a solar umbrella. Most ideal point for that is the Sun-Venus L1. A 10000km big foil would be enough. Note, its mass, for example in the case of a 0.1mm width, is still years of the whole steel production of the today Earth. You also have a problem with the stability, but that you can solve by utilizing light pressure and the non-pointlikeness of the foil.

  2. You need water. Or, considering that there is oxygen in the planet enough, already in the atmosphere but also in the soil, only hydrogen. There is simply no way to transfer the required amount of hydrogen there. Note, we don't need oceans on the Venus, it is enough if a planetery water pipeline network can irrigate its soil, but we still need millions of cubic kilometers. Contrary the common belief, simple ice meteors and similars would not work: simple there is not enough in the whole solar system. What possibly might work: maybe billions of artificial satellites in the external solar atmosphere could accelerate protons there with focused and well-controlled magnetic fields.

These are the most crucial problems to solve. None of them is solvable in the foreseeable future, not even with Musk technologies. What probably would be needed:

  • VASIMR, i.e. well designed and long lasting ion drives, to move in the solar system anywhere.
  • Time. Very, very long time. For example, getting into close solar orbit requires ten years due to the tricks of the orbital mechanics, even with partial ion thrust.
  • Robots. Nothing will produce and control, for example, a billion of interplanetar transfer devices. We, humanity, are simply too less for it. The work to be done, would require billions of years of work of the Humanity of the today. We simply can not do that. So, we need to build factories, the factories need to build robots and the robots will do the work.

I believe, we need at least centuries for these, even in the best case scenario, however we practically can not see the future of the humanity more as some decades.

However, if these two is done, only "nuances" remain. Namely:

  1. We need a magnetic field. Venus has no magnetic field, generating secondary radiation in the atmosphere which is incompatible with the long-term life. Beside that, it is also taking away the atmosphere, particularly the lightest atoms (hardly acquired hydrogen).

The Venusian magnetic field could be done by a simple circular conductor around the equator. It would be hard, and it would also require tremendous amount of power. Or, if it is superconductor, then its cooling would need. Except if we already have developed room-temperature superconductivity, which looks achievable in centuries timescale, extrapolating the past successes. But it is not guaranteed. But that is achievable. Once I calculated for that, we would need maybe a square meter section copper cable around the equator - it is hard but not unimaginable. It helps a lot that the magnetic field does not need to be very strong. Our own one can only rotate a needle if we build it for that.

  1. We need to react the Hydrogen and the Carbon Dioxide of the atmosphere, to get... water, carbon and oxygen. Obviously that is not the "natural" process, so we need to prevent the carbon to again re-oxidize, best if we dig it deeply into the Venusian soil.

Possibly there would not be enough oxygen - note, that Martian atmosphere, converted with hydrogen to water, would only lead to some tens of meter of average water height. The average depth of water would be 2.5km if it would be distributed equally on the Earth.

In this case, additional oxygen could be extracted also from the soil. Oxygen is actually the most abundant element in the planetary crusts, it is only bound too strongly, mostly to various metals - aluminium, iron, magnesium and so on. Needless to say, extracting oxygen from the soil requires a tremendous amount of energy. Imagine that the whole Venusian surface is filled with solar panels (or nuclear power plants), and with robotic factories. Again, we, Humanity, are simply not enough for that. So we would need to build factories to build robots, which build thousand times more factories to build atmospheric reprocessor plants.

And, again, we also need time. Once I calculated the energy need of such a transformation, and compared to the energy what the Venus gets as solar radiation. It would be more like a millenia long project.

  1. Surprisingly, using living beings, like unicellular things or plants, would be likely not effective. There is no water, there is no oxygen, there is nothing there, only some percent of salt would kill most life. Maybe genetical engineering would help, but honestly why? Robotic systems are much more effective, particularly in the beginning.

  2. As I explained above, actually the atmosphere can be processed to water and coal mines, that is not problem. Beside the carbon dioxide, there is also about 3-4 bar of nitrogen in the Venusian atmosphere, that is already tolerable in my opinion.

  3. Problem of the sulphuric acid in the atmosphere would quickly solve itself as a side effect. As the water content grows and the plant cools, the sulfuric acid would react to sulphates with the soil and it would become insert. Also the Earth soil has more or less sulfate nearly everywhere, it does not a problem anywhere.

  4. Also the Venus does not rotate. More clearly it rotates, but very slowly. We need weather control. That could be done making the umbrella initially shading the whole planet, then making it partially transparent (for example, by opening "windows" on it) we could say, where do we want Sun. Note, it would not solve the problem of the rear side, there would be still month long nights with very small temperatures. So, the weather control would not only need to create an ambient temperature on the light side, but it should also somehow create such at atmospheric movement where the dense nitrogen atmosphere helps to transfer so many heat to the dark side as possible.

I think the total timescale of the whole project is at least a millenia long. Doing some similar on the Moon would only need some centuries.

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You cannot fix carbon dioxide into carbonates until the surface cools. We would probably need seas and we are way above the triple point of water. We would want to seed the atmosphere with some self-replicating lifeforms that would extract carbon from the atmosphere, and excrete some of it as graphite, which would fall as black snow on the surface. This would increase the oxygen content of the upper atmosphere, which may give you convective cells where heat splits 2 C02 -> 2 CO + O2, which rises, and then gives the reverse reaction (burning carbon monoxide) at the surface. This will probably be confined to the upper atmosphere as the extra pressure at the surface would favour CO2 even at the higher temperatures.

Even if we could fix the atmosphere, the surface is going to remain hot for a long time. Newton used his law of cooling to estimate the time it took for the surface of the Earth to cool from red heat, assuming everything was the same temperature as what comes out of volcanoes. He came up with some figure of hundreds of thousands of years.

No matter what you do to Terraform Venus, it is going to be a long term job. And the surface is going to be unbearably hot for a long time. Plenty of time to set your story.

The bit you might have trouble explaining is why people are terraforming Venus at all if the return on investment is so slow. You might want to explain it as a by-product of extracting carbon from the atmosphere to make dirigibles to live in, or measures to calm the terrific winds so people can inhabit the lower levels.

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Catalytic conversions. Need high pressure. Check. Heat Check. Catalytic converters. Flow in and check.

All that is needed is a heat pump, to concentrate the already present heat. Turn that canyon into a terraforming tool, by coating it with a fractal surfaced catalytic. Heat resistant solartarp over head and your electrically charged and good to go - all you need is a pressure differential- as provided by a eternal storm for example.

Chemistry that is hard on earth, does not have to be hard elsewhere if you start to see the "hostile" circumstances as part of the reaction. Ideal would be a catalyzing stage, that does not need additional workstages, like this: https://www.nature.com/articles/s41467-022-28456-9

Or needs ocassional cleanup by burning out the accumulating byproducts. (carbon needs a clean, carbon monoxide not). Even more preferable if its almost impervious to the elements - if they are accidic. https://pubs.acs.org/doi/10.1021/jacs.9b10061

So.. what is still needed, is a janitor. Somebody has to go out there and clean up that catalyst, every cycle. And that lead rain - and those accidic rivers. Its a shit job, but someone has to do it. Someone has to swing that broom for that venus-surface boom.

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