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B Could we shade the Earth from the Sun to save Earth?

  1. Sep 6, 2017 #1
    Saving Earth - for a while: Could we shade the Earth from the Sun at a rate that keeps up with the Sun’s increase in Luminosity?

    There is a theoretical Dyson’s Ring that could be built around the Sun that would be used to tap the energy of the Sun. Could we construct something like that to shade enough of the Sun to extend the life of Earth as the Sun’s luminosity increases 10% every billion years. In effect, we would need to construct a permanent partial solar eclipse. Once built we just need to add on as the Sun’s luminosity increases. As I understand it we have about ½ billion years to get this up and running - initially blocking only 5% of the Sun.
     
  2. jcsd
  3. Sep 6, 2017 #2
    It would be simpler to give the Earth rings. In fact, as our satellites collide with each other, it's starting to happen already - and it's a problem.
    A Dyson sphere would be a major project to say the least.
     
  4. Sep 6, 2017 #3
    Now that I think about it, it may be easier to move the Earth than to build a Dyson sphere.
    The Earth is already expected to head outwards as the sun grows - from solar tidal effects. If we can accelerate that effect, perhaps we could dodge the sun as it turns into a red giant.

    But we are probably better off leaving the planets as they are - or perhaps bumping Earth up very slightly to clear the sun as it becomes a red giant.
    For one thing, we may not want to start cooling the Earth quite yet. According to Berger and Loutre, in another 50,000 years, we may be in for some chilly times.
    http://science.sciencemag.org/content/297/5585/1287

    Also, as the Earth become uninhabitable, Mars and Jupiter will be warming up. And it would certainly be easier to move the human race than to move a planet or build a Dyson sphere.
     
  5. Sep 6, 2017 #4
    Sadly, that report is pay-walled...
     
  6. Sep 6, 2017 #5
    Last edited by a moderator: Sep 7, 2017
  7. Sep 7, 2017 #6

    jim mcnamara

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    @stoomart I get permissions issues on the link.
     
  8. Sep 7, 2017 #7
    Is it fttp? Typo? In the forum it's not even posted as a link (i.e. it's not highlighted blue ...).
     
  9. Sep 7, 2017 #8

    DrClaude

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    Now fixed.
    No. FTP stands for File Transfer Protocol, only 1 t (HTTP is HyperText Transfer Protocol).
     
  10. Sep 7, 2017 #9
    Looks like PF does't allow linking to FTP files, since the corrected link omits the protocol prefix "ftp://". I tried reposting by adding an explicit link, and it comes back as "ftp//" which won't work, so my only suggestion is to copy/paste the URL sting into a new browser tab. Any ideas @Greg Bernhardt?
     
  11. Sep 7, 2017 #10
    ftp appears to not be recognized and appends "http://" to the ftp url.
     
  12. Sep 7, 2017 #11

    Drakkith

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    It's probably far easier to build reflective or high-albedo surfaces on Earth than to try to shade it from the Sun, though I'm sure the latter is possible, even if not exactly feasible.
     
  13. Sep 7, 2017 #12
    Thanks for checking, this link should work for those without C or V keys:

    https://tinyurl.com/akerkwg
     
  14. Sep 8, 2017 #13

    DrClaude

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    Doesn't work for me. Anyway, the link in post #5 has been fixed and should work.
     
  15. Sep 9, 2017 #14

    stefan r

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    No, I have to argue. Moving earth is not easy. You would need a plausible scheme to get the energy necessary and momentum necessary. If you are solar collecting the energy then you already have a Dyson Sphere. If you are assuming fusion power (or insert or energy source) then you still need to radiate the heat away. The radiators would either still be a Dyson swarm or the fusion reactors would do the heat damage that you wanted to avoid.

    You could collect energy from light in the ecliptic plane. Then you would not need to waste the energy trying to move earth.

    A cheaper and easier way to do this is parking a structure near the Earth-Sun Lagrange point 1. You could block 5% of the sun's light using a little more than 2.5% of the earth's surface area. You need a little extra so that you can reflect sunlight at angles and keep station. The structure is not really at the L1 point because light pressure would accelerate it. So it needs to be parked sunward from L1.

    A better version is to use a film that blocks infra-red and/or UV light but allows most of the visible spectrum through. Leaving the frequencies used by plants could have benefits for agriculture and maybe wildlife. So a shade with around 5% of the earths surface area made out of a thin film.
     
  16. Sep 9, 2017 #15
    I would not want be a project leader for that scale of engineering.
    I expect a lot of people would get upset about it to the point of trying to assassinate me.
     
  17. Sep 9, 2017 #16

    stefan r

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    Each statite could be the size of a typical football field. 5% of earth's surface area is 2.5 million units if each averages 100 km2. I am not aware of any NASA employees getting assassinated. I think you could build one without worry.

    Unlike most suggestions for climate engineering the statite swarm would be very easy to remove and control. Compare to drakkith's suggestion:

    In order to get a 5% reduction in solar energy adsorbed you have to modify much more than 5% of Earth's surface. Relatively dark surfaces reflect some sunlight. Covering water with aluminum foil or styrofoam might increase surface albedo 90%. A lot of radiation is adsorbed by the atmosphere before or after it reflects off the aluminum. The surfaces would be difficult to maintain because of Earths weather and atmosphere. Earth rotates so reflectors only work part of the day. So even larger swathes of earth need to be subjected to bleaching. Floating/dumping 250 million square kilometers of styrofoam into the oceans would cause "a lot of people would get upset".
     
  18. Sep 9, 2017 #17

    phinds

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    I'll bet the fish would be pissed off too.
     
  19. Sep 9, 2017 #18
    yeah, I think I'll try collecting photons from pulsars.
    Something to do.
     
  20. Sep 9, 2017 #19

    Drakkith

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    I think it's the opposite. If, say, 20% of the surface absorbs 70% of the incoming light, then altering 1/4 of that part of the surface (5% of the total surface area) would drop the total absorption by up to 17.5%.

    But that 5% represents more than 5% of the illuminated portion of the Earth when it is in daylight (up to 10%). I'd expect the numbers to even out to a 5% drop, but I admit I haven't done any math on this.

    Absolutely.
     
  21. Sep 11, 2017 #20

    olivermsun

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    The ocean surface is mostly a pretty big absorber. On the other hand, white sand deserts and new snow/ice are pretty good reflectors and also tend to exist in places with a good long wave window.
     
  22. Sep 12, 2017 #21
    No need for the first ftp:// just sayin
     
  23. Sep 13, 2017 #22
    Earth could be shaded one day as a byproduct of other things- https://en.wikipedia.org/wiki/Space-based_solar_power
    So if your wondering.....if everyone has the same standard of living as Canadians, they would consume 20kw energy pp and at 10B future population that is 200TW global energy. This would require 142 000km 2 collecting area (at 100% efficiency) and block out .1% of all sunlight earth receives(less on a practical level).
    * It would be self defeating in some way, as you are emitting energy in infrared, that goes to Earth, as well as beaming the energy down to earth.....unless you beam that energy somewhere else......
    Regards
    Smartalek
     
  24. Sep 15, 2017 #23

    sophiecentaur

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    Hear hear. I have often advocated painting the Sahara Desert and other open spaces with white paint or covering it with reflective foil. You could miss the difficult bits like mountain sides and big rocks. Still, a 10% portion of the Earth's surface would need a lot of paint. It makes me laugh to read stuff that people write about "terraforming Mars" when you realise that the idea of terraforming Earth is constantly being rejected. It would be cheaper than doing Mars AND we would all benefit from it!
    Manufacturers could pay a tax which would correspond to a certain area (10m2, say, of the Earth being rendered reflective for every kg of carbon produced in the manufacture of every item.
     
  25. Sep 18, 2017 #24
    I appreciate all the posts. It turns out that this is in part an old idea. There is a Wikipedia site named Space sunshade but these solutions are all in response to Global Warming not extending the life of the planet when the "habitable zone" no longer includes Earth. So from that perspective, it seems to be a new idea. I think that in the near future we could develop the technology to do this and maybe every 5 or 10 years send up a L1 station that would block or reflect enough solar energy to keep pace with this natural increase. The result would be an Earth with basically the same climate we have today a billion years in the future.
     
  26. Sep 18, 2017 #25
    Since Sun's evolutionary luminosity increase is very slow, it might make sense to move Earth farther from the Sun.

    One way which seems possible is to place an asteriod very slightly closer to Earth than L4 Lagrange point, so that it slowly "falls towards Earth" - which in turn, exerts a force on Earth which, over many years, slowly widens its orbit. Install high-Isp engines (such as ion engines) on that asteroid to keep it from drifting relative to Earth.
     
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