Yeah, I know. Of all the real estate in the solar system, Venus is the least hospitable of all the terrestrial planets. Still, I ask the question:[ul]“What are the obstacles to terraforming Venus, and how (theoretically, of course) might they be overcome?”[/ul]I suppose the biggest problem is how could we “deflate” Venus’ dense atmosphere? Even if it weren’t hot and toxic, that’s still a biggie.
~~Baloo
I remember sitting in a bar with a buddy of mine, with him telling me what a great time this was in which to be living, since we’ll start terraforming planets any time now. My response to him was: science can’t even accurately predict the weather for four days in advance on this planet, where we’ve lived since the beginning of time, because we don’t understand how all the different systems work together. To think that we could move to another, completely foreign planet and understand its systems well enough to terraform it is wishful thinking at best.
That’s the point at which he punched me and told me not to rain on his parade.
Venus fact sheet.
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
Earth fact sheet.
http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
Obstacles to terraforming? How about Venus’ really hot and dense atmosphere?
Earth: Average temperature: 288 K
Venus: Average temperature: 737 K
Earth: Surface Pressure: 1014 mb
Venus: Surface Pressure: 92 bars
Earth: Surface Density: 1.217 kg/m3
Venus: Surface Density: ~65. kg/m3
http://nssdc.gsfc.nasa.gov/planetary/factsheet/planet_table_ratio.html
Before you can start terraforming, you’re going to have to invent machinery that will operate under extreme conditions of heat and pressure.
Other than that, a non-tech solution, I have great faith in the power of Mother Nature. If you could design a delivery system for some kind of algae that wouldn’t be crushed by the tremendous heat and pressure (there are algae and bacteria that grow in geothermal hot pools and mud pots), then you could bomb the surface of Venus with algae and then sit back and wait a million years or so. Seriously. I don’t see why this wouldn’t work.
C’mon, pipeliner, where’s your can-do spirit? 
DDG, no machinery is required (at least in the beginning, IMHO - nobody’s going to want to live there at that point). Algae will help, but if you want the environment to support them you need to make it comfortable for them first. Extremophiles (like the Archaea that live in hot springs) are often anaerobic chemosynthetic critters, which means that they don’t photosynthesize and produce O2 as a by-product, which would be what we’d need.
IMHO, one of the biggest obstacles apart from the atmosphere is Venus’s proximity to the Sun. Even if you were to alter the atmosphere so that humans could breathe it, the incoming solar radiation would be too intense. Can you imagine the sunburn? 
Another major problem is lack of water on the surface.
My recipe for terraforming Venus (assuming that we had the ability and the patience to wait, both major assumptions):
[ul]
Build a sunscreen in front of the planet. A total block would be helpful initially to give a kick-start to cooling the Venusian surface, but eventually you’d want to adjust the screen to let in enough solar radiation to make things comfy.
Once the surface of has cooled sufficiently, bring in water (via comet). Lots of it. You’d like to create oceans on the surface, because oceans have great capacity for storing CO2. The oceans should suck out an appreciable quantity of CO2 from the atmosphere. Once the CO2 goes into solution, it forms carbonic acid and its dissociation products, bicarbonate and carbonate.
Dump a lot of calcium in the water. The bicarbonate will combine with the calcium and precipitate as limestone. Recognizing that importing enough calcium from earth would be tough, you can hope that there are enough Ca-silicate rocks present on Venus that can weather, releasing Ca into the oceans (else you’ll need to truck in a load of basalt from the moon). Precipitating limestone will draw CO2 out of the ocean, and subsequently the atmosphere.
The time has come to set up an ecosystem. You’d need to provide enough nutrients in the ocean for various types of plankton, especially those that secrete calcite (or aragonite) shells. Get the ecosystem up and running, and the critters could start generating oxygen for you as well as help keep CO2 in check (in essence, creating a carbon cycle for Venus).
[/ul]
From start to finish… probably an awfully long time, especially for steps three and four. Once it is habitable (or close to it), you’d also need to find a way to deal with the fact that a Venusian day is nearly as long as a year. So, do folks slowly migrate around the world to keep up with the Sun? Agriculturalists might. Or do you set up stations wherever convenient and let people deal with living in the dark for half a year? Hey, some Scandinavians do that already. 
Very long-term possible problems with this scenario… if Venus isn’t sufficiently tectonically active, then eventually the carbon cycle will break down. CO2 needs to be injected into the atmosphere somehow, and Ca-silicates have to be made available for weathering and CO2 drawdown; the two processes are needed for counterbalance. (On Earth, volcanic eruptions and mountain-building events take care of this issue.) Our very-distant descendants might think it a little too expensive to keep up, and eventually abandon it.
Simple. Tow it out to one of the lagrange points on earth’s orbit so it can be at the proper distance to cool off; at the same time, tow one of the really big moons from the outer gas giants in to be the moon for Venus. This’d suck off all the excess atmosphere.
While you’re at it, bring Mars in to the other lagrange point on earth’s orbit, then call down some big blocks of ice from the rings of Saturn so there’d be water to work with. Maybe you’d want to do that before moving it away from Saturn, though…
Anyway. Simple. From here on in it’s just scribbling.
Actually, Fillet, IIRC, the reason Venus is so hot is not because of proximity to the sun, but because of the greenhouse effect. The atmosphere is so thick that radiation which enters cannot escape, instead being reflected back towards the surface. So, instead of building a giant heat shield, you really need to convert the chemical makeup of the atmosphere to allow escape of trapped radiation. Whether Venus would then be too hot because of solar proximity, I dunno.
Also, AFAIK, Venus does not have sufficient tectonic activity. In fact, although I could be wrong, I believe it has no tectonic activity at all, owing to a lack of surface plates.
The problem isn’t Venus’ hot, dense atmosphere per se, it’s the difficulties involved in:
[list=1]
[li]what makes it hot[/li][li]what makes it dense[/li][li]Hi, Opal![/li][/list=1]
However, let’s look at these, with a bit of handwaving thrown in as necessary.
One of reasons for Venus’ being hot is, of course, the fact that it gets about twice as much energy from the Sun as does the Earth. Therefore, we need a mirror. A really big mirror. A thin, mylarized silicone sheet orbiting Venus in the ecliptic is probably the best that we can do. Putting the mirror in a cytherocentric orbit, or even at the Sun-Venus L1 point, would have it just too far from the planet to cast much of a shadow unless it were really, really big, and, whilst I am willing to wave my hands, I’m not willing to wave them so vigorously that they fly off of my wrists. Therefore, a (fairly) closely orbiting mirror. We may wish to put several of these in orbit, to reflect the maximum amount of light (although in that case we can have problems with radiation from Venus) and arrange them so as get a decent day-night cycle (ISTR that the sideral period of Venus (essentially, the time between the sun being overhead at the equator, and the sun being overhead again at the equator, is 117 days). Manufacturing the mirrors is an exercise left to the student.
The atmosphere of Venus is mostly CO[sub]2[/sub]; contrary to popular belief, however, that’s an effect of the temperature, not a cause of it. The Urey reaction is:
CO[sub]2[/sub] + *X*SiO[sub]3[/sub] <-> *X*CO[sub]3[/sub] + SiO[sub]2[/sub]
or, in layman’s terms, carbon dioxide and silicates will be in equilibrium with carbonates and silica (essentially, sand). The Urey reaction runs to the right at lower temperatures, to the left at higher temperatures, and faster (but not fast enough to do our terraforming project any good, alas) in the presence of liquid water. Earth has about the same amount of CO[sub]2[/sub] that Venus has; however, the Urey reaction on Earth has gone almost completely to the right, Venus, almost completely to the left. Sulfuric acid is one of the real culprits in the Cytherean “runaway greenhouse”.
Now, Venus has very little water at present; it probably outgassed the same amount as the Earth, but the water has long since been photolysized by solar UV, the hydrogen escaping and the oxygen combining with the regolith. We will want to bring in both water and an alkali (to neutraliz the sulfuric acid); fortunately, we can get both in the outer system in the form of impure water ice laced with ammonia ice and/or ammonium hydroxide. The task of delivering it is again left as an exercise for the student.
Even cooled down, Venus’ atmosphere will remain a problem. Assuming that we convert the carbon dioxide to oxygen by handwaving, we still have about 30 atmospheres of oxygen – a wee bit too much for Terrestrial life.
More should be said on this, but I have to devote my attention to other, more mundane things (like earning a living) just now.
Just making a large square or circle of aluminized mylar as big as the planet would probably not work. It’d be unstable and would fold and bend. Instead, I suggest that the screen be composed of a very large number of long thin strips that would overlap slightly. You’d have to connect them together with monofilament lines to keep them in place.
Now to make it adjustable, you have to make the monofilament lines connected in such a way that by pulling on the ends of the lines, the strips would all tilt in the same direction, letting the sunlight through in between the strips. And what we then have is
(wait for it)
the Venusian Blind!
Necros, it is too hot now because of the greenhouse effect of CO2. The present atmospheric composition is thought, though, to have been the result of water loss related to the fact that the surface was too warm to keep water in liquid form (water stayed in vapor form and was broken down at the top of the atmosphere by solar radiation; H2 escaped into space, O bound to minerals on the surface). So if we’re going to change the atmospheric composition to something more earth-like, excessive solar radiation is a big problem to address. I went through some of those numbers in this recent thread about the chances of Earth becoming Venus-like. Plus I see now on preview that Akatsukami has run through some numbers as well.
For my model (admittedly spur-of-the-moment), before you change the atmosphere it needs to be cool enough to permit liquid water. If you block all incoming solar radiation, Venus will begin to lose heat - it has too, because the energy balance is no longer maintained. There are other ways to alter the atmosphere, I’m sure, but you’ll still have to do an end run around the Sun to make Venus livable.
I’ve admittedly not kept up with the latest on Venusian tectonism or lack thereof; last I heard there was still some possibility for it, although nowhere near as much as on earth (or perhaps a different style). Anyone have a recent cite?
Ha! I love it!
Impressive, but a mite too slow for my liking. Rather than use the old cytherocentric mirror technique, why not just divert a 100-mile asteroid through Venus’ upper atmosphere at, say, 75,000 kph?
Presto! Change-o! No more atmosphere. Now, you can rebuild from a clean slate.
Next, soft-land Jupiter’s moon, Europa, on Venus and allow the sun’s naturally “warming” rays to liberate the trapped water and oxygen to create an instant atmosphere.
As a last step, the winning government contractor is responsible for removing the dehydrated moon from Venus and disposing of it properly.
Lesson: You’ll never get anywhere if you don’t think big.
Chronology of all Venus flybys and missions.
http://nssdc.gsfc.nasa.gov/planetary/chronology_venus.html
Sputnik 7 - 4 Feb 1961 - Attempted Venus Impact
Venera 1 - 12 Feb 1961 - Venus Flyby (Contact Lost)
Mariner 1 - 22 Jul 1962 - Attempted Venus Flyby (Launch Failure)
Sputnik 23 - 25 Aug 1962 - Attempted Venus Flyby
Mariner 2 - 27 Aug 1962 - Venus Flyby
Sputnik 24 - 1 Sep 1962 - Attempted Venus Flyby
Sputnik 25 - 12 Sep 1962 - Attempted Venus Flyby
Cosmos 21 - 11 Nov 1963 - Attempted Venera Test Flight?
Venera 1964A - 19 Feb 1964 - Attempted Venus Flyby (Launch Failure)
Venera 1964B - 1 Mar 1964 - Attempted Venus Flyby (Launch Failure)
Cosmos 27 - 27 Mar 1964 - Attempted Venus Flyby
Zond 1 - 2 Apr 1964 - Venus Flyby (Contact Lost)
Venera 2 - 12 Nov 1965 - Venus Flyby (Contact Lost)
Venera 3 - 16 Nov 1965 - Venus Lander (Contact Lost)
Cosmos 96 - 23 Nov 1965 - Attempted Venus Lander?
Venera 1965A - 23 Nov 1965 - Attempted Venus Flyby (Launch Failure)
Venera 4 - 12 Jun 1967 - Venus Probe
Mariner 5 - 14 Jun 1967 - Venus Flyby
Cosmos 167 - 17 Jun 1967 - Attempted Venus Probe
Venera 5 - 5 Jan 1969 - Venus Probe
Venera 6 - 10 Jan 1969 - Venus Probe
Venera 7 - 17 Aug 1970 - Venus Lander
Cosmos 359 - 22 Aug 1970 - Attempted Venus Probe
Venera 8 - 27 Mar 1972 - Venus Probe
Cosmos 482 - 31 Mar 1972 - Attempted Venus Probe
Mariner 10 - 4 Nov 1973 - Venus/Mercury Flybys
Venera 9 - 8 Jun 1975 - Venus Orbiter and Lander
Venera 10 - 14 Jun 1975 - Venus Orbiter and Lander
Pioneer Venus 1 - 20 May 1978 - Venus Orbiter
Pioneer Venus 2 - 8 Aug 1978 - Venus Probes
Venera 11 - 9 Sep 1978 - Venus Orbiter and Lander
Venera 12 - 14 Sep 1978 - Venus Orbiter and Lander
Venera 13 - 30 Oct 1981 - Venus Orbiter and Lander
Venera 14 - 4 Nov 1981 - Venus Orbiter and Lander
Venera 15 - 2 Jun 1983 - Venus Orbiter
Venera 16 - 7 Jun 1983 - Venus Orbiter
Vega 1 - 15 Dec 1984 - Venus Lander and Balloon/Comet Halley Flyby
Vega 2 - 21 Dec 1984 - Venus Lander and Balloon/Comet Halley Flyby
Magellan - 4 May 1989 - Venus Orbiter
Galileo - 18 Oct 1989 - Jupiter Orbiter/Probe (Venus Flyby)
Cassini - 15 Oct 1997 - Saturn Orbiter (Venus Flyby)
From Magellan, 1989–
http://nssdc.gsfc.nasa.gov/planetary/magellan.html
http://www.star.ucl.ac.uk/~idh/geology/venus.htm
And spend some time with Dr. Bindschadler.
http://www.agu.org/revgeophys/bindsc01/bindsc01.html
Dude.
And thank you, Fillet, so much for making me go look up Venus missions. I got to be reminded of the ghastly dangers we of Planet Earth incurred during the Cassini fly-by. Remember that? Its plutonium fuel cell was going to explode just as it was going past the Earth and cook us all.
http://www.astro.psu.edu/users/nahks/sts_page/sts_flyby.html
So, did we all die in 1999? I can’t remember.
Anyway, I can’t find anything involving any Cassini data that might pertain to Venusian tectonics. Evidently the Big Brains ain’t done chewing it over.
Maybe somebody else can go look for “Galileo data Venus tectonics”. Gotta run.
I think everyone did die, DDG. Did you miss the ride on Hale-Bopp previous? Sucks to be you. We’re all posting from Alpha Centauri.
IIRC, Venus had more of elastic crust than one based on plates. I’ll have to check the real words of my cites, though, tonight.
Thanks, Fillet, for correcting me on the sequence of events there on ol’ Venus.
Ah, so desuka, terraforming Venus, part deux.
We have a problem, in that there doesn’t seem to be any way to genuinely terraform it in less than geological time. As I previously noted, although Earth and Venus seem to have about the same amount of CO[sub]2[/sub], Earth’s is now in the form of carbonate rocks, whilst Venus’ is the form of gas. We can envision a tailored alga that would float at the correct (i.e., tolerably warm) altitude in the atmosphere, converting carbon dioxide and water to oxygen and carbohydrates (although we will have introduce more water; of course, we’d have to do that anyway). However, we need some way to sequester the reduced carbon, which would otherwise sink to the surface and be reoxidized there.
Having converted the CO[sub]2[/sub] to O[sub]2[/sub], we still have far too much of the latter. “Gardening” (turning over) the crust to expose fresh, un- or inadequately-oxidized might well work (although it may have all been oxidized by oxygen from photolyzed water), but naturally it takes megayears to do so. If we can get just the right sequence of reduction of radiation, CO[sub]2[/sub] breakdown, carbon sequestration, and crustal oxidation, we might succeed that way. but I don’t want to try and put together the project plan.
Oh, and tsunamiurfer writes:
If I have to write an EIS for this project, fahgeddiboutit. If Moses had had to fill out the forms wanted when he parted the Red Sea, the Torah would be written in Egyptian. 
Er… One thing I don’t understand; why would Venus need to have tectonic activity in order to be terraformed. Are you saying that we would need to introduce tectonic activity for some reason? Why would we want to?
Land sakes, DDG! I hope you cut and pasted that list. Thanks for all the cites.
Necros, you’re welcome. It’s not all that often I get to use some of the guff floating around in my head in a creative fashion, so please forgive me if I seem excitable. Actually, if you have refs about Venus with an elastic crust, I would love to take a look - I’ve had a soft spot (so to speak) for Venus since I took an undergrad planetary geology class, but just haven’t had time to keep up with it since.
Akatsukami - why not just stuff the EIS with every synonym for “massive” and leave it at that?
wevets - Plate tectonic activity here on Earth helps to keep long-term biogeochemical cycles functioning in ways that make Earth life happy. Volcanoes (found along plate boundaries) inject CO2 into the atmosphere that’s needed for photosynthesis, while the formation of mountain belts (also along plate boundaries) exposes silicate rocks that draw CO2 out of the atmosphere as they weather (it’s a check that prevents too much CO2 buildup). While biological activity has a significant impact on relatively short geological timescales, you need crustal-oriented processes to keep things balanced for the long haul. So if Venus has no significant plate tectonic activity to speak off, it becomes difficult to support the terraform changes on the scale of millions of years. (Of course, that would be a moot point for humans, but who cares? )
Good thinking, Fillet, the really long term cycling never occurred to me. Anything over a couple thousand years just woooshes right over my head anyway.
OK…instead of a mirror, could we “cloud” the planet with a specially made type of dust? The specks of dust would have to be somehow polarized to block UV light (coming from the sun) while allowing IR light (radiated from the planet) to pass through.
This would take away much of the energy that the planet receives, while still allowing it to bleed off some of its stored heat.
Does such a substance exist?
As for a moon…what’s wrong with using Mercury?
-David
Ha! You kill me!
~~Baloo
Venus has hardly any surface cratering which is surprising even though it has 90x the atmosphere as Earth. One very interesting theory that I read was that because Venus has no volcanos or plate tectonics, heat & pressure build up beneath the crust over a long period of time. That is until a critical point is reached and the entire crust melts from the inside out, completely resurfacing the planet and erasing the craters on a semi-regular basis.
Sounds lovely…can’t get rid of that problem with a mirror or algae.