Cold New Dawn

The scenario outlined above (Figure 7.10) for terraforming Venus is just one of the many that have been proposed. It is difficult to estimate exactly how long the precipitation process might take to transform

External agent

External agent

Surface

Figure 7.10. A schematic timeline (time increasing to the right) for the Oberg--Fogg terraforming scheme for Venus. The process begins by adding hydrogen and cyanobacteria to the present atmosphere and ends by evoking a ''Big Rain'' stage to produce a new Venusian ocean and a breathable atmosphere.

Surface

Figure 7.10. A schematic timeline (time increasing to the right) for the Oberg--Fogg terraforming scheme for Venus. The process begins by adding hydrogen and cyanobacteria to the present atmosphere and ends by evoking a ''Big Rain'' stage to produce a new Venusian ocean and a breathable atmosphere.

Venus, but somewhere between 104 and 106 years is the usual estimate of time required. Some researchers feel, however, that this sort of time scale is far too long, and accordingly they advocate the implementation of more rapidly acting terraforming schemes. British engineer Paul Birch, for example, has suggested one highly technical approach to terraforming Venus that begins with a massive atmospheric freeze out. For Birch, the terraforming process begins with the construction of a massive sunshade, located at the Venusian L1 point, with the sole purpose of blocking out all of the incident sunlight.

Cloaked in the freezing darkness of permanent night, the Venusian atmosphere will begin to cool, according to Birch's calculations, at rate of about 5°C per year. Within 100 years, therefore, the temperature will have fallen to near 273 K (or 0°C). Birch further estimates that within 200 years of the beginning of the Venusian darkness the temperature will have dropped to a level at which the atmospheric CO2 will begin to freeze out. in short order, a solid glacial blanket of carbon dioxide ice will coat the entire surface of Venus.

Birch further suggests that it would be wise to selectively illuminate the highland areas of Venus so that these could be colonized relatively rapidly. The driving idea here is that by allowing for some regions to be quickly inhabited and ''worked'' there would be some early return on investments process. However, this kind of activity commercializes the terraforming process. If humanity cannot move beyond its current focus on short-term investment and rapid-return economics, then it (and terraforming) has no future.

To continue with Birch's scenario, after the freeze out has been completed, and before sunlight can once again be allowed to illuminate the planet, the CO2 ice layer must be covered and insulated against subsequent sublimation. Birch suggests that this might be achieved by laying down a layer of linked, artificially produced hollow rocks. One might also initiate the large-scale exportation of CO2 ice from the planet. Clearly, this latter process will consume a considerable amount of time, certainly longer than the initial few hundred years of the freeze-out phase. Birch's argument, however, is that it can be achieved in an ongoing, expansive manner, with economics driving the process. Indeed, while Venus might be rich in CO2 ice and mineral deposits after its freeze out, it will require the importation of massive quantities of water to support the Venusian colonies.

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