November 26, 2013
Imagine Orbiting Light Shields To Cool Venus

Some climate scientists believe that when the sun was less bright Venus had an atmosphere more like Earth. Then Sol's light output went up 30%.

Deflecting 30% of the Sun's light from Venus would require massive orbiting sheets of metal (aluminum?). Could transhumans 100 years from now pull off such a feat?

Cooling Venus seems more appealing than trying to make Mars hospitable. Mars lacks an atmosphere and is too distant from the Sun.

Share |      Randall Parker, 2013 November 26 08:22 PM 

Kudzu Bob said at November 26, 2013 9:39 PM:

Would the sheets really have to be all that massive? Might it be possible to make them out of some sort of material that is, say, only a molecule thick?

Ambacti said at November 27, 2013 1:08 AM:

Hot rock always outgasses CO2. Earth avoided the fate of Venus largely through CO2 consuming organisms. This article suggests that a cloud of water vapor set the greenhouse effect off early on Venus, preventing life from taking hold. At this point the problem is not so much the sun, as the dense outgassed CO2 blanket that envelops Venus. Genetically engineered photosynthetic organisms seeded into the atmosphere might do the trick.

Vektor said at November 27, 2013 5:23 AM:

These massive sheets would also have to act as a protective magnetic field. The Venusian magnetosphere is much weaker than Earth.

philw1776 said at November 27, 2013 9:13 AM:

Cooling is the easy task. The problem is sequestering 100 Earth atmospheres of CO2. If we could move asteroids around we could try blasting much of it into space. The EPA would have a cow.

Tim said at November 27, 2013 3:54 PM:

Your kidding I asssume about Venus being easier to work with than Mars? I mean all I would have to do is build factories on Mars producing Nitrogen Trifloride 17,000 time more potent than CO2. Just enough to start the CO2 frozen in Martian regolith out-gassing, in a few decades you would have earth-like atmospheric pressures and temperatures

A gas used in manufacture of flat panel televisions, computer displays, microcircuits, and thin-film solar panels is 17,000 times more potent a greenhouse gas than carbon dioxide, and it is far more prevalent in the atmosphere than previously estimated. The powerful greenhouse gas nitrogen trifluoride, NF3, is at least four times more widespread than scientists had believed, according to new research by a team at Scripps Institution of Oceanography at the University of California, San Diego.

Brett Bellmore said at November 27, 2013 4:46 PM:

Why bother? At 50-60 km altitude, both the pressure and temperature of Venus' atmosphere are quite Earthlike. Granted, the actual atmosphere there is mostly CO2, with sulfuric acid clouds, but humanly breathable air is about half as bouyant in CO2 as Helium is in air; People could live inside aerostats, whole ecosystems could be floated in the clouds.

Randall Parker said at November 27, 2013 8:10 PM:


What's your source for the Earth-like atmospheric pressure on Mars if the frozen CO2 warms up?


Both Mars and Venus need a stronger magnetic field.


We need sufficient hydrogen to bind to the oxygen to make water. Given low enough temperatures we'd then get oceans. Then just turn the carbon into pure solid carbon. We need hydrogen on both Mars and Venus. Where to get it?

Tim said at November 27, 2013 8:54 PM:

Computer calculations performed by myself, Owen B. Toon and James F. Kasting suggest that if Mars's atmosphere contained just a few parts per million of the super-greenhouse gases, the average temperature at the planet's surface would rise from -60 to -40 degrees Celsius (-76 to -40 degrees Fahrenheit). This warming could be enough to trigger the release of carbon dioxide from the polar caps and soil into the atmosphere. Carbon dioxide would then augment the greenhouse effect even further, driving the release of more carbon dioxide and water vapor into the atmosphere. Such positive feedback would be sufficient to create a thick, warm atmosphere--the carbon dioxide Mars. - Dr. Christopher McKay

McKay suggests that the entire PFC process will take a mere 100 years before average global temperatures reach an Earthly level. This number is such good news that scientists who were once skeptical of the concept of terraforming now look forward to the day when they can take part in it. And that day may be closer than anyone might imagine

Carbon dioxide sublimation[edit]

There is presently enough carbon dioxide (CO2) as ice in the Martian south pole and absorbed by regolith (soil) on Mars that, if sublimated to gas by a climate warming of only a few degrees, would increase the atmospheric pressure to 30 kilopascals (0.30 atm),[16] comparable to the altitude of the peak of Mount Everest, where the atmospheric pressure is 33.7 kilopascals (0.333 atm). Although this would not be breathable by humans, it is above the Armstrong limit and would eliminate the present need for pressure suits.

Ronald Brak said at November 28, 2013 5:51 AM:

Venus's atmosphere is plenty thick enough to stop radiation without a magnetic field, as is earth's. But if the earth suddenly lost its magnetic field solar wind would start to strip away the atmosphere, which is what happened to mars, but it would be a very slow process. Much slower than for mars because although the solar wind is more intense in earth orbit the earth's higher gravity makes it considerably harder for our air to be lost.

As for cooling venus, I can't remember the exact figure, but if all sunlight was blocked it would apparently take thousands of years to cool down to an earth like temperature, so one wouldn't want to be in a hurry.

As for which would be easier to terraform, mars or venus, I'd have to say mars. All it really needs is a roof. Now roofing a planet may sound hard, but compared to cooling venus and dealing with its excess atmosphere it should be a doddle.

Tim said at November 28, 2013 9:40 AM:

Well also remember, from my link above: "There is presently enough carbon dioxide (CO2) as ice in the Martian south pole and absorbed by regolith (soil) on Mars that, if sublimated to gas by a climate warming of only a few degrees, would increase the atmospheric pressure to 30 kilopascals (0.30 atm),[16] comparable to the altitude of the peak of Mount Everest, where the atmospheric pressure is 33.7 kilopascals (0.333 atm)."

Atmospheric pressure is the weight of the air pressing down on the planet. Mars's gravity is only .38 of Earth's. So the actual mass of Mars's atmosphere after the CO2 is outgassed must be, .333atm/.38 = .876 atmosphere. So in terms of actual mass, the amount of air would be pretty comparable to earth's.

Ronald Brak said at November 29, 2013 9:36 AM:

When I said mars just needs a roof before I should perhaps have mentioned that it doesn't need to be shingles nailed to two by four planks. A very thin membrane surrounding the planet might do. It might be so thin that air could still diffuse through it but by using solar power it could actively uptake desired gases and pass them back into the membrane and undesired gases could be kept out. While obviously beyond our ability at the moment it might be the cheapest way to terraform mars in terms of energy actively spent. It also has the advantage that there is no need to start with covering the whole planet. Just a crater or a valley might do at first.

Tim said at November 29, 2013 12:39 PM:

The colonies on Mars would probably be in the lowlands, where liquid water would tend to pool after the CO2 had been out-gassed (and the air pressure is higher). From my link: "Significant amounts of water are stored in the south pole of Mars, which, if melted, would correspond to a planetwide ocean 11 meters deep". Domed over craters and/or maybe that very long deep canyon on Mars. The high canyon walls would give protection from Solar flares and Cosmic rays. You could even run super-conducting cables across the top of the canyon, run a charge through them to deflect away the charged partices of both flares and cosmic rays.

Ronald Brak said at November 29, 2013 8:25 PM:

Looking at radiation levels on mars I see a bubble habitat would have to be huge to hold enough atmosphere to keep cosmic rays to under 20 mSv a year. So maybe they should just roof the whole planet from the get go.

Of course if making earth type environments is the goal then building space habitats is probably the way to go as they can just about be made as earthlike as you like, but thinking about terraforming is still interesting.

Brett Bellmore said at December 1, 2013 5:03 AM:

Is there any fundamental reason why Mars couldn't be provided with a sufficient magnetic field, by just building a large superconducting loop around its equator?

Engineer-Poet said at December 1, 2013 5:30 AM:

Perhaps by reversing that magnetic field at a sufficient frequency, the interior of Mars could be re-melted by induction and plate tectonics resumed.  This would recycle the planetary crust and free the CO2 and water that's currently bound in it by weathering.

Brett Bellmore said at December 1, 2013 5:01 PM:

That would require an amount of energy high enough we'd need to become a K-2 civilization to do it. The magnetic field I think we could manage before even K-1.

Now, if you could put a large asteroid into a highly elliptical orbit around Mars, you might be able to do that heating by tidal effects. But alternating magnetic fields have a way of radiating away.

Engineer-Poet said at December 1, 2013 8:30 PM:

Earth's internal heat seepage is milliwatts per square meter, far less than the radiative forcing from anthropogenic GHG's.  Generating a few tens of TW to re-heat Mars' core and mantle would be nothing for a civilization which can lay a superconducting cable around it in the first place.  Powersats would do it, and that only takes 1970's technology.

Brett Bellmore said at December 2, 2013 3:19 AM:

The internal heat seepage may be small, but the heat *capacity* is rather large. The specific heat of lava, per a quick search, is about 1600 J/Kg/C. Multiply that by 6e23 Kg, and a modest 500 degrees. 5e29 Joules. I estimate that, if you had a solar collector the size of Mars, you could do it in about 4e14 seconds, (Assuming a generous 25% efficiency from sunlight to hot rock.) Huh, better than I thought, only ten million years or so. I think you could use comets to supply the gas a *little* faster than that.

Engineer-Poet said at December 2, 2013 4:48 AM:

You could probably do spot-heating of volatile-rich zones a lot quicker.

Since the goal of terraforming Mars is to have it terraformed for the long term, a ten-million-year project timeline isn't too bad.  Setting it up so that it's viable for half a billion years (given solar brightening) without further maintenance would be good; I'd have to crunch numbers to see if that's practical.

My understanding is that Mars has been stripped of much of its hydrogen by UV dissociation and the solar wind.  Adding volatiles is probably a good idea.  Maybe half a bar of CO2 and a bar of nitrogen from Venus?  Water from comets; why should we waste the ISON's on light shows?

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