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Extracts (5)

Take raw Venus. CO₂ atmosphere of ninety-five bar, temperature at surface would melt lead, hotter even than Mercury’s brightside. A hellish place. On the other hand, .9 g, and just a tad smaller than Earth. Two continental rises on the surface, Ishtar and Aphrodite. Earth’s sister planet. There’s real potential here for a great new creation.

Take one Saturnian ice moon—Dione will do fine. Dismantle with Von Neumann self-replicating excavators, cutting it into chunks about ten kilometers on a side. Attach mass drivers to the chunks and send them down to Venus.

While doing this, 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.

Now take the chunks of Dione you have been saving and crack them against each other in the oxygen-and-buffer atmosphere at the correct height to create steam and rain. This will add back to the planet some heat, which at this point has been taken below the human-friendly range. Possibly some light can be let through the sunshield if needed to help heating. It will only take two years for the greater part of the impact water to rain and snow onto the surface, so be ready to work fast.

The water on the surface after this Dione infusion will be equal to about 10 percent of Earth’s water. It will be freshwater; salt to taste. The water will cover 80 percent of Venus, which is much flatter than Earth, to an average depth of 120 meters. If deeper seas are preferred, but also a maximum amount of land, consider digging an oceanic trench with some of the Dione impactors. Remember this will complicate the CO₂ sequestration if you choose to do it, so make adjustments accordingly. If it is done carefully, however, Venus could ultimately end up with about twice the land surface that Earth has.

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.

Which option you choose is your preference. Think about what you want in the end, or, if you don’t believe in endings, which process you prefer.