One way to terraform Venus would be to create a massive sun shade enveloping the planet. How much actual material would be required for this? And where would you get it from?

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    $\begingroup$ Do you mean a sphere completely surrounding the planet or a disk in between the planet and the sun? (How would you keep either in place?) $\endgroup$
    – Tim B
    Sep 5 '18 at 22:26
  • $\begingroup$ The construction method really rather matters here, but I think that some of the calculations around blocking out the light to Earth may be of use. $\endgroup$
    – Joe Bloggs
    Sep 5 '18 at 22:33
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    $\begingroup$ VTC as POB because in the current state answers to this question can vary wildly and still be valid. Previous comments mention nature of the problem. $\endgroup$
    – dot_Sp0T
    Sep 5 '18 at 22:49
  • $\begingroup$ Venus is not habitable not only because of the heat, but because of many other things, including the CO2 (which then affects heat). A better way to cool down the planet would be to get rid of the CO2 first. $\endgroup$
    – Gimelist
    Sep 5 '18 at 22:51
  • $\begingroup$ You said this is one mentioned way - where was it mentioned? If you provide some context, it might be more clear what kind of shade we're looking it. $\endgroup$
    – Cadence
    Sep 5 '18 at 22:52

About 53-ish cubic kilometers of material, assuming that it is only 0.1mm in thickness.

Of course, how you would keep it on station or keep the solar wind from blowing that uber thin 13,000km disk into the planet would be a different problem.

  • $\begingroup$ How many CubeSats worth of sails is that? $\endgroup$ Sep 6 '18 at 0:47
  • $\begingroup$ @MichaelKutz Yeah... that looks to be about 7x10^14 cubesats, assuming a 10 square meter Nanosail 7.5 micrometers thick which is a lot less thick than the 100 micrometer I assumed for the sunshade. [;) $\endgroup$
    – Ian Moote
    Sep 6 '18 at 0:56
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    $\begingroup$ @IanMoote Don't forget all the micro meteors that will likely turn it into swiss cheese $\endgroup$
    – Shadowzee
    Sep 6 '18 at 2:14
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    $\begingroup$ @tbrookside I don't believe so. The Sun is much larger than both the shade and Venus, so the light would skirt around it quite a bit, like the penumbra of an eclipse. This illustrates it pretty well, from the Wikipedia article about penumbras and antumbras: upload.wikimedia.org/wikipedia/commons/2/2e/… So, if anything, it would have to be larger. The closer you get to Venus the smaller you can get away with -- roughly 13,000km diameter. $\endgroup$
    – Ian Moote
    Sep 6 '18 at 3:12
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    $\begingroup$ Looking at the revision history of the question I cannot find any evidence to your claim on top of your answer? Where do you take that info from? $\endgroup$
    – dot_Sp0T
    Sep 6 '18 at 6:42

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