Terraforming Venus

...build a round sunshield of lunatic aluminum, very thin material, only 50 grams per square meter and yet still totaling 3 x 1013 kilograms, the largest thing ever built by humans. Concentric strips give the sunshield flexibility and allow it to tack up into the solar wind to hold its position at the L1 point, where it will shadow Venus entirely. Deprived of insolation, the planet will cool at a rate of five K a year.

After 140 years, the CO2 atmosphere will have rained and snowed to the surface and frozen as a layer of dry ice. Scrape all the dry ice that landed on Ishtar and Aphrodite down to the lowlands, being careful to keep a smooth surface. While clearing off the continents, release another suite of Von Neumann self-replicating chemical factories designed to break oxygen out of the frozen CO2; these will create 150 millibars of oxygen for the atmosphere, in about the same time it takes for all the CO2 atmosphere to freeze. A purely oxygen atmosphere would be too flammable, so add a buffer gas, preferably nitrogen, to make a more stable mix. Titan may be oversubscribed for its excess nitrogen, so be prepared to seek substitutions. Argon mined on Luna would also serve in a pinch.

When you have the oxygen you want, and the dry ice all flat on the lowlands, cover the dry ice with foamed rock, so that the CO2 is a completely sequestered feature of the lithosphere.

[...]

At this point (140 years freezing and preparation, 50 years scraping and poaching, so be patient!) you might think that the planet is ready for biological occupation. But remember, combining the Venusian year of 224 days with its daily rotation period of 243 days, you get a screwball curve (retrograde motion, sun rising in the west) in which the solar day for any particular point on the planet is 116.75 days. Tests have long since determined that that’s too long for most Terran life-forms to survive, tweaked or not. So at this point, two main options have been identified. First is to program the sunshield so that it lets through sunlight to the surface and then blocks it off again, flexing like a circular venetian blind to make a more Terran rhythm of night and day. This would make it easy on the new biosphere, but would require that the sunshield work without fail.

The second option would call for another round of impactor bombardments, this time striking the surface of the planet such that their angular momentum spins the planet up to something like a fifty-hour day, which is considered within the tolerance limit for most Terran life-forms. The problem with this option is the way it would delay occupation of the planet’s surface, by its release of a considerable amount of the sequestered dry ice under the foamed rock layer. Biosphere establishment would have to be put off for another two hundred years, effectively doubling the time of terraformation. But there would be no further reliance on a sunshield. And a properly constituted and maintained Venusian atmosphere could handle full sunlight without greenhousing or other spoilage.

A fictional account of incredible engineering.