Robert Zubrin (RZ): Yes.<br /><br />AM: Does Mars contain all of the elements needed to make the planet habitable, or will we have to import gases, chemicals, etc., from elsewhere? If so, then will Mars always need constant inputs to achieve habitability, or do you think that given enough inputs Mars would reach a tipping point and planetary processes would create a self-sustaining feed-back loop?<br /><br />RZ: It appears that Mars does have all the elements needed for terraforming. The one outstanding question is nitrogen, whose inventory remains unknown. However theory suggests that Mars should have had an initial supply of nitrogen comparable to the Earth, and it seems likely that much of this is still there.<br /><br />AM: How long will terraforming take? When you envision a terraformed Mars, what do you see?<br /><br />RZ: If one considers the problem of terraforming Mars from the point of view of current technology, the scenario looks like this:<br /><br />1. A century to settle Mars and create a substantial local industrial capability and population.<br />2. A half century producing fluorocarbon gases (like CF4) to warm the planet by ~10 C.<br />3. A half century for CO2 to outgas from the soil under the impetus of the fluorocarbon gases, thickening the atmosphere to 0.2 to 0.3 bar, and raising the planetary temperature a further 40 C. This will cause water to melt out of the permafrost, and rivers to flow and rain to fall. Radiation doses on the surface will also be greatly reduced. Under these conditions, with active human help, first photosynthetic microbes and then ever more complex plants could be spread over the planet, as they would be able to grow in the open. Humans on Mars in this stage would no longer need pressure suits, just oxygen masks, and very large domed cities could be built, as the domes would no longer need to contain pressure greater than the outside environment.<br />4. Over a period of about a thousand years, human-disseminated and harvested plant