Inventory of CO2 available for terraforming Mars
Short form: a study of just how much CO2 Mars actually has… in the atmosphere as gas, in the polar ice caps, bound up in rocks. Conclusion: if it was all released into the atmosphere, the atmospheric pressure would rise to about 20 millibar, though 15 millibar is more achievable. And not only is this a very low pressure, meaning you’d still need a pressure suit outside, it would also lead to a trivially small temperature increase due to the greenhouse effect.
In shorter form: ain’t enough CO2 for terraforming.
So… bomb the place. Redirect comets to dump water and CO2 onto Mars to build up atmospheric gases. Easy? Nope. Cheap? Hell no. Fast? Ha.
To first order, on Earth the atmosphere at sea level produces the same pressure as being under ten meters of water. So if a ten-meter-deep ocean of water suddenly covered all of Mars and evaporated into water vapor, would that give an Earth-like atmospheric pressure? Not quite… Mars surface *gravity* is less than Earth: 3.711 m/sec squared compared to 9.807 m/sec squared. So that magical ocean of water vapor would produce 0.3784 of an atmosphere. Which is probably good enough. So how much *mass* of an atmosphere is that?
NOTE: Corrected math and conclusions below…
The surface area of Mars is 144,798,500,000,000 m2. A ten-meter-thick layer of water at 1 kg/cubic meter would be 1,447,985,000,000,000 kilograms. Call it a quadrillion and a half kilos, or a trillion and a half tons. Halley’s comet has a mass of about 220,000,000,000,000 kilos… 0.22 trillion tons. Granted: the bulk of the nucleus would be non-volatile materials… dust, rock, meh. But it would *seem* that plowing ten good-sized comets into Mars would provide enough atmospheric gas to jumpstart an atmosphere. One decent comet would provide more of an atmosphere than all of the gases already in situ. Place all the dark flowers you like on the surface of Mars. Place all the solar mirrors into orbit around Mars you like. Nothing will help as much as cometary bombardment.