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neilzero
2013-Aug-09, 01:44 AM
Bump: From the old "How bright would a terraformed Venus be Thread?"

Van Rijn

2012-Mar-24, 08:03 PM

And to terraform Venus, especially if it is given a lot of water, a lot of that sunlight will have to be reflected away, either with something in the Sun-Venus L1 point, or in low orbit, or in the atmosphere (some type of world girdling structure, lots of reflective balloons, etc.). There probably would be additional reflectors to give a reasonable day-night cycle too (far more feasible than trying to change the Venusian rotation rate). It's possible you could have a partially terraformed, very dry Venus without doing this, but for something that is supposed to be very Earth-like, it's pretty much a given that there would have to be so much modification that these would swamp other issues affecting Venus's brightness in the sky.
~ I agree: Sunshades are needed to cool Venus even if it has zero greenhouse gas which would not be Earth like, so Venus would appear darker, especially when farthest from Earth. The huge sunshades would often be 5th to 10th magnitude and would look like tiny moons of Venus, unless they were in the upper atmosphere which is likely more costly than statite shades. Please hijack this thread with any Venus terraforming details.~ Neil

neilzero
2014-Jun-13, 09:24 PM
This thread would have gotten a dozen comments and rebuttals three years, plus ago. What has happened to Cosmoquest? I've forgotten why I thought sun shades in the upper atmosphere of Venus would be more costly than statites = seems unlikely now, for the same amount of cooling and life expectancy of the sunshades. I still think extremely costly at Venus-Sun L1 because the sun is not a point source.

eburacum45
2014-Jun-18, 06:01 PM
This thread would have gotten a dozen comments and rebuttals three years, plus ago. What has happened to Cosmoquest? I've forgotten why I thought sun shades in the upper atmosphere of Venus would be more costly than statites = seems unlikely now, for the same amount of cooling and life expectancy of the sunshades. I still think extremely costly at Venus-Sun L1 because the sun is not a point source.
I'm just a little confused as to why you started a new thread instead of adding to one of the old threads. Unlike other forums, there isn't really a taboo against adding to old threads here, as far as I am aware.
Here's one thread about this subject
http://cosmoquest.org/forum/showthread.php?99462-Terraforming-Venus-project

You may be right. A layer of Storrs Hall's Weather Machines could reduce the temperature of Venus somewhat; these are gas-filled diamondoid spheres, each equipped with an actively controlled mirror. The sort of technology that might be commonplace a hundred years or so from now when we start looking as Venus in earnest. The spheres could be made from Venusian carbon, and filled with Venusian nitrogen, which is a lifting gas. Here's an image of Storrs Hall's idea (image made by me).
http://www.orionsarm.com/eg-article/4f9fb6b195cda


On the other hand Venus already has a very high albedo, and raising it by a few percent would only cause a very slow cooling. If you are prepared to wait then this option is likely to be considerably cheaper than the L1 sunshade,

Barabino
2014-Jun-24, 08:08 PM
but if the tiny mirror-carrying spheres are inside the greenhoused atmosphere, how are they supposed to subtract heat?

Noclevername
2014-Jun-24, 08:13 PM
but if the tiny mirror-carrying spheres are inside the greenhoused atmosphere, how are they supposed to subtract heat?

They remain in the upper atmosphere where greenhouse gasses are thinner and heat does not absorb easily. Venus' atmosphere is deep.

Van Rijn
2014-Jun-26, 12:11 AM
You may be right. A layer of Storrs Hall's Weather Machines could reduce the temperature of Venus somewhat; these are gas-filled diamondoid spheres, each equipped with an actively controlled mirror. The sort of technology that might be commonplace a hundred years or so from now when we start looking as Venus in earnest. The spheres could be made from Venusian carbon, and filled with Venusian nitrogen, which is a lifting gas. Here's an image of Storrs Hall's idea (image made by me).
http://www.orionsarm.com/eg-article/4f9fb6b195cda


That's a very similar idea to one I had years ago that I called "smartdust." I later saw somebody else use the same name for a similar idea. Essentially, the idea was to have small active machines/balloons that could change their reflectivity.

For Mars, they would mostly become dark while on sunside and reflective on the nightside, but some could be reflective on the sunside. The percentage would vary to maintain surface temperature within the preferred range. For Venus it would be the reverse - mostly reflective on the sunside, etc.. For Earth, they might go either way, depending on current surface temperature (so no more ice ages or extremely warm periods). I wasn't looking at them so much for the terraforming process itself, but to maintain temperature long term. Perhaps really long term, like a billion years.

Conceptually, they might be self replicating, have machines that themselves are self replicating that produce them, or perhaps a bioengineered plant to produce them. If a plant, it would probably be a good idea to give them exceptionally good DNA self repair capability like radiodurans - you don't really want these things evolving into something that might not produce the dust, or different dust. That holds true however they replicate, of course.

For a story idea, I was going to refer to this type of technology as "Gaiatech" - technology that can maintain a planet in a preferred state. Unfortunately, there's a company with that name, so I scratched that.

cjameshuff
2014-Jun-26, 01:15 AM
Maybe something as simple as balloons with a silvered or blackened bottom half and transparent upper half. In the sun they act as greenhouses, heating up and becoming more buoyant, rising to higher altitudes and shielding the lower altitudes from the sun. At night, they cool and sink, reflecting heat radiated downward back up toward the sky. The overall effect being to increase daytime albedo and nighttime emissivity.

Barabino
2014-Aug-10, 04:45 AM
But... does a place on Venus get chillier by night? Really sure about that?

Noclevername
2014-Aug-10, 05:54 AM
But... does a place on Venus get chillier by night? Really sure about that?

Thermal scans of Venus say the temperature is pretty even over the surface.

cjameshuff
2014-Aug-10, 05:29 PM
Firstly, it's the surface/lower atmosphere temperature that is nearly constant, the atmosphere at high altitudes is less so. Second, my idea doesn't need or even benefit from day-night temperature changes in the atmosphere, it relies on the balloons having a larger temperature swing than the surrounding atmosphere.