Mass colonization of Mars will require advanced space capabilities. There will need to be hundreds or even thousands of fully reusable SpaceX BFR. A study that shows that Terraforming Mars needs to go beyond blowing up the Mars Ice caps shows that more advanced capabilities like placing a magnetic shield at Mars L1 or placing large orbital mirrors will be needed to Terraform Mars. Fortunately if we have thousands of SpaceX BFR then placing large structures in Mars orbit or at Mars L1 will also be possible.
They looked at recent space mission analyses of the abundance of carbon-bearing minerals and the occurrence of CO2 in polar ice from the Mars Reconnaissance Orbiter and the Mars Odyssey spacecraft. They did not look at technology beyond what is currently available. This was an invalid restriction because you will only terraform Mars if you already have thousands living on Mars and plan to put millions on Mars.
Mars has enough CO2 for 15 millibars of pressure which is 65 times less than the pressure of 1,000 millibars at Earth’s sea level. Strip mining and processing the Nili Fossae mineral deposits would add 15 to 150 millibars.
Mars needs at about 65 millibars to reach the Armstrong limit. The Armstrong limit is where water does not boil at body temperature. Processing half of the Nili Fossae mineral deposits gets to that amount. The Mars atmosphere currently weighs 25 trillion tons. Getting to about 230 trillion tons is the Armstrong limit. Five times more is about the equivalent of the summit of Everest. Three times more than Everest pressure is Earth Sea level. Getting past the Armstrong limit would mean people could walk around with just an oxygen mask.
Martian atmosphere has a mass of 25 teratons, need to add at least another 200 teratons (200 trillion tons).
Getting to Everest pressure would take about 1300 trillion tons of Mars atmosphere. It will take about 4000 trillion tons to get to one earth sea level pressure.
Elon Musk has talked about giant nuclear or giant solar heating of the soil. Others have talked about massive orbital solar mirrors.
A magnetic shield at the L1 of Mars and Sun could be used to protect the Mars atmosphere. This could allow any volcanic activity on Mars to accumulate atmosphere.
Reservoirs and sinks for CO2 that they looked at are polar CO2 ice or water-ice clathrate and CO2 adsorbed onto mineral grains in the regolith and carbon-bearing minerals (in carbon-ate-bearing rocks. Mars currently has an average pressure of about 6 mbar — equivalent to about 15 g CO2 cm–2 at the surface.
The most accessible CO2 reservoir is in the polar caps. The CO2 ice there could be readily mobilized by heating of the deposits. This could be done by, for example, using explosives to raise dust into the atmosphere so that it would deposit on the polar caps, effectively decreasing their surface albedo and increasing the amount of absorbed solar energy. This could also be done by utilizing explosives to heat the polar ice directly, thus triggering sublimation. If the entire Mars polar-cap CO2 were emplaced into the atmosphere, it would increase the pressure to less than 15 mbar total and, while about twice the current Martian atmospheric pressure, this is well below the needed ~1 bar.
Carbonate-bearing mineral deposits could be heated to release their CO2. The typical decrepitation temperature for carbonates is around ~300 °C. This is high enough that it could not be achieved by solar heating from greenhouse warming, and would thus require some form of deposit processing. They limited such processing to the Nili Fossae soil deposits, large-scale strip-mining would put probably less than 15 mbar and certainly no more than 150 mbar of CO2 into the atmosphere, assuming a complete mobilization process. Although other deposits that hold more CO2 exist or could possibly be identified, processing those would be more difficult due to either their diffuse distribution or their currently unknown location and, therefore, their deep burial beneath the surface.
Lower air pressure means there would be less warming. An atmosphere of 20 mbar would cause Mars warming of less than 10 K. Mars needs to be warmed ~60 K to allow liquid water to be stable. It would take a CO2 pressure of about 1 bar to produce greenhouse warming that would bring temperatures close to the melting point of ice.
Elon has talked about using nuclear energy technology to power the processing of Mars Soil. The researchers looked at the Nili Fossae soil deposits. It would take at least six times the soil processing of the Nili Fossae soildeposits to achieve Mars terraforming.
— Discover Magazine (@DiscoverMag) July 31, 2018
There’s a massive amount of CO2 on Mars adsorbed into soil that’d be released upon heating. With enough energy via artificial or natural (sun) fusion, you can terraform almost any large, rocky body.
— Elon Musk (@elonmusk) July 31, 2018