Talk:Terraforming

How much must be added to the atmosphere for terraforming?

We can figure out the mass of the atmosphere on Earth and from that estimate what is lacking on Mars. Atmospheric pressure results from the weight of the atmosphere between the planetary surface and outer space. Over every square inch of Earth's surface at sea level there is a one square inch column of air reaching to outer space that weighs 14.7 pounds. 99.9% of the atmosphere is below the altitude of 34 miles. At that height there are only about 0.9% more square inches than there are at the surface. So we can estimate the mass of Earth's atmosphere as 14.7 pounds times the number of square inches of Earth's surface. That overestimates the mass by neglecting the fact that there is no air in the space taken up by mountains. That overestimation is the figure we want for estimating the mass of gas needed to be added to Mars' atmosphere. The radius of Earth is 3.96 E 3 (3960) miles. So the area equals 1.969 E 8 (19690000) square miles or 7.906 E 17 square inches. So the atmosphere of Earth weighs 1.16 E 19 pounds or 5.28 E 18 kilograms. To get the amount of gas needed to have an atmospheric pressure on Mars equal to Earth sea-level pressure we multiply by the ratio of Mars' area to Earth's area by the ratio of Mars' gravity to Earth's gravity. This underestimates the mass because Mars' atmosphere extends to heights at which the gravity is less than the surface gravity and overestimates the mass because it neglects the lessening of the scale height on Mars by the higher average molecular weight of the gas we will use (carbon dioxide, sulfur hexafluoride and 1,1,1-trichloroethane). We assume that the combined effect of these factors is insignificant. So the mass of atmosphere needed on Mars is 3.89 E 15 metric tons. If we raise the pressure to only one tenth of Earth's sea-level pressure and only one tenth of the atmosphere is to be added manufactured gasses, then these gasses would mass 3.89 E 13 metric tons. Spreading the manufacture of the gas over 1000 years we get 3.80 E 10 metric tons per year or 4.44 E 6 tons per hour. The Edmund Fitzgerald carried 26,000 tons. So, what would be needed would be 170 Edmund Fitzgerald cargo mass equivalents per hour for a thousand years. --Farred 05:57, 8 September 2010 (UTC)

Doctor Robert Zubrin and Doctor Christopher McKay came up with a somewhat different figure for the amount of artificial greenhouse gases needed to be manufactured to raise the atmospheric pressure of Mars. They published Technological Requirements for Terraforming Mars For a 10 degree centigrade rise in temperature they suggest that 878 tons per hour of greenhouse gasses over a period of 20 years would be sufficient. This in turn should trigger a run-away greenhouse effect until all carbon dioxide available to be released into Mars' atmosphere is released. They suggest that for a 500 millibar reservoir of carbon dioxide in the polar caps and the soil of Mars and a characteristic energy of releasing carbon dioxide from the soil of 20 K, the atmospheric pressure should stabilize at 400 millibar and the temperature at 1 C. There are problems with that. First, there is the unknown characteristic energy of releasing carbon dioxide from the soil and the unknown amount of carbon dioxide in the planetary reservoir waiting to be released. Zubrin & McKay suggest that manned exploration will provide the answers. Second, the equilibrium temperature they indicate allows some lakes to form in the equatorial region. Water and a thick carbon dioxide atmosphere on Mars means carbonate rocks will form, which will take the carbon dioxide out of the atmosphere again until the greenhouse effect is no longer sufficient to sustain the liquid water. Then Mars will freeze over again, like it did the last time this happened, billions of years ago.

Why do Zubrin and McKay get their futile terraforming for so much less manufactured greenhouse gasses than I indicated? I picked 10 millibars out of a hat as the partial pressure of greenhouse gasses that would be sustained and they used 4 hundred-thousandths of a millibar as the needed partial pressure of greenhouse gas to raise the temperature on Mars 10 K. Zubrin & McKay's figure may be more reasonable, but there is still plenty worth discussing on this topic. --Farred 22:53, 21 September 2010 (UTC)