What we know is that Mars has an abundant source of carbon
dioxide. This premier greenhouse gas is trapped in the poles or in the planets
regolith. In order to terraform Mars, both sources will be used, however, the carbon
dioxide in the poles will initiate the process.
The natural process of terraformation can be initiated by melting the poles. Although this seems an immense task, studies have shown that a small but sustained change in temperature at the south pole can initiate a runaway greenhouse affect which would result in evaporation of the polar cap. As the ice evaporates, global temperature and pressure will increase and as a result, the carbon dioxide held in the regolith will begin to be liberated. In short, a four degree increase at the pole could result in a ten to twenty degree increase globally. Although it seems that a four degree increase is miniscule, the global climate that is Mars is so complex that changing one element can have a profound effect. The carbon dioxide in the pole can be characterized by a measure known as vapor pressure. This characteristic is a measure of the tendency of carbon dioxide to turn to a vapor state. With the ambient temperature of the South pole being 147 degrees Kelvin (273 degrees kelvin is equal to 0 degrees celsius), the vapor pressure of carbon dioxide is 6 millibars. At this equilibrium position, it is nearly impossible to have large amounts of carbon dioxide in the atmosphere.
However, if we can increase the temperature, the vapor
pressure of carbon dioxide would increase, releasing more of the greenhouse gas into the
atmosphere, and increasing the atmospheric pressure. Although vapor pressure and
atmospheric pressure are two different concepts, they are related in that the higher the
vapor pressure of a certain gas, more of the gas is released into the atmosphere,
resulting in more gas in the atmosphere which translates to higher pressure. Since
both the vapor pressure properties of carbon dioxide and the greenhouse effect of the gas
are known, we can predict what the conditions on Mars will be like after the carbon
dioxide is liberated, which is the first step to terraforming Mars. It is believed
that there is enough frozen carbon dioxide to increase Martian pressure to 100
millibars. As atmospheric pressure increases, polar temperature increases almost
exponentially. Similarly, as polar temperature increases, vapor pressure would
increase, and as a result, atmospheric pressure increases, creating a runaway greenhouse
effect.
Then, considering a 4 degree Kelvin increase, a runaway greenhouse effect would result and evaporate the etire pole in less than a decade. Also, when the temperature and pressure rise enough, the runaway greenhouse effect would continue without further heating. Therefore, if the heating were stopped, the atmosphere would remain intact. As the polar cap evaporates, the greenhouse effect's dynamics caused by the carbon dioxide become an issue. By themselves, they could provide Mars with a 400 millibar atmosphere. However, all of the reserves are impossible to release because as the heating change releases the reserves, the vacated area becomes like a dry and provides huge amounts of resistence in the effort to let the carbon dioxide go. Unfortunately, we enocunter a huge unknown quantity. This is the energy value required to release the reserves from Martian regolith (or the temperature of desorption). Through calculations, the amounts of carbon dioxide in the pole and Martian regolith would be able to be released and cause a 500 millibar atmosphere (as opposed to the 6 millibar atmosphere which currently exists there). There has also been questimates as far as where equilibrium would exist as far as the atmosphere when both sources of carbon dioxide are being released. This point is calculated at approximately 300 millibars when both sources of gas have been exhausted. Also, through the greenhouse effect, the possible temperature for the Tropical region in the summer (when the atmosphere would thicken) approaches and maybe even reaches 273 degrees Kelvin. This is important in respect to the idea of terraforming because it's the melting point of ice and would result in the melting of water ice and permafrost.
On the other hand, these figures are based on a
temperature of desorption of 20 degrees K. If this unknow quantity is much higher
than is expected, then the resulting atmosphere would be a very small millibar
quantity. However, it is possible to use substitute methods of inducing a greenhouse
effect. These such ideas reside in things like releasing factory made CFC's into the
already existing atmosphere and producing similar effects as the conventional method with
a desorption temperature of 20 degrees. These procedures would result in an
atmosphere of nearly a couple hundred millibars and at any temperature of
desorption.
Finally, there is one more unknown that may play a large factor in the terraforming of
Mars. This unknown is the available sources of carbon dioxide. After all, the
larger the amount of carbon dioxide that can be released, the thicker the atmosphere that
can be created. In each possible scenario, the raising of the desorption temp
lower's the possible high temperature and the millibar total for the Martian atmosphere.
These factors especially don't help a carbon dioxide poor Mars which would already
create lower top temperatures and lower millibar atmospheric conditions. However, it
has been shown that if the mean temperature of 20 degrees over the native carbon dioxide
reserves' produced temperature is maintained, then a believable atmosphere and acceptable
pressures can be even if the temperature of desorption is a rediculously high value of 40
degrees Kelvin. The main thing to be concluded from all of these facts, figures, and
scenarios is that the resulting atmospheric conditions from the regolith/ atmosphere
system are very dependent on the unknown values which are being encountered but can also
be counteracted by careful planning, instituting of effective methods of change, and ideas
that can make this change in atmospheric condition more predictable or more easy to
handle.