Fixing Carbon in Venus's Atmosphere

Question

I often wonder about fixing the carbon the atmosphere of Venus.

Whilst there is no water meaning this is unlikely to be possible using biological means, is it possible that some kind of machine could do this?.

The answer to this question doesn't rule out carbon fixing without water, but does suggest it is beyond our current capability.

Suppose that fixing is possible by some kind of floating machine in the upper atmosphere, energy should not be a problem, sunlight and wind should be plentiful.

Further suppose that the machine fixes the carbon into hollow shapes, essentially carbon balloons. With enough machines operating over a long enough time period, probably a geological era even with self replicating machines, what would be the effect on the Venusian atmosphere?.

I like to imagine Venus being blanketed with these carbon balloons, they could even be made in shapes that naturally interlock to create a kind of surface high above the real surface.

What would be the effect of such a blanket 20cm thick?, I often speculate that the temperature underneath the blanket would plummet, perhaps causing the CO2 to liquify, further reducing the atmospheric pressure at the (real) surface.

With the atmospheric pressure and temperatures reduced, would we see renewed volcanic activity?, would Venus expand noticeably?.

How would such a scenario be likely to end?, would the carbon blanket be weathered away or turned back into CO2 some other way?.

Putting aside the scale of such a venture, how feasible is any of this?.

Answer 1

1. take a fairly big metallic asteroid in the 25+ kilometer range from the inner NEA asteroid belt and by means of slow acceleration and slingshotting haul it in to a venus orbit.

2. keep adding solar sells and create an automated industrial infrastructure on that asteroid

3. produce reflective material and start engineering a microfilm think layer around the orbital plane of venus. Reflect sunlight away from the equatorial zone around venus.

4. Reduce incoming sunlight reaching the venusian clouds gradually to under 10% over a few decades. Given sufficient means of production this can easily be achieved with a several 10km asteroid. More than enough raw materials.

5. Wait. Temperature will drop on venus. Venus is baked hot through and through, and the cooling down, i.e. radiating away heat, will take an absurd long time. There simply isn't a sensible way to cool Venus down. The only way that will do anything is adding the solar shielding (in a polar orbit probably) to well over 95% reflectivity. At that rate it makes even more sense to saturate the upper atmosphere with a reflective fillament "floating" on top of the atmosphere.

This will take a few centuries. I think we'll colonize and industrialize the Kuyper belt and Mercury before we tackle Venus.

Edit: Early stages of this project may resemble the world depicted in Larry Niven's "plateau", where the planet proper is toxic and uninhabitable, but "a few mountain plateau's stick high above the atmosphere. As the terraforming advances you may see high tower structures erected on the surface, in some cases 50 kilometers or more high, where there's cities and industrial activity. Compare the norwegian troll platform - it's pillars are hollow down to the ocean floor - a full hundreds of meters. With active, assertive cooling (?) and hyper-advanced heat resistant materials it may eventually become feasible to start erecting meaningful real estate. Right now such towers would have to resist extreme pressures, corrosive winds, blast furnace heat and that would require various types of uhm, unobtaneous constructs.

Answer 2

As carbon balloons block more sunlight, the temperature would slowly drop, if you could block the sun all at once it is estimated the CO2 would totally freeze out in just 200 years. Though the 3 atm of N2 would still be in the atmosphere.

With a CO2 ocean, which would cause very intense weathering of the Venetian surface during the 'big rain', plate tectonics would possibly be restarted due to the surface liquid ocean and with it volcanism. The planet would not expand as the same amount of mass is being applied to the surface whether in liquid or gaseous form.

Working over such big time scales maintaining the balloons/planet shield will be necessary, dealing with the acid in atmosphere wearing down the shield, the solar wind directly pummeling the shield, occasional meteor impacts, adjusting the altitude and shape as the pressure drops underneath the shield, etc.