This is a subject that interests me, so I hope you'll take all of this with a grain of salt. ;)
Could it be made habitable, and how?
1). Add volatiles, mainly water, carbon dioxide ( for biomass and oxygen ) and amonia ( for Nitrogen ) in the form of comets. This will thicken the atmosphere and warm the planetary surface.
2). Increase the amount of sunlight that the planet receives - build thin film reflectors in orbit around mars.
3). Add the appropriate micro-organisms to convert the atmosphere into something human breathable.
Over all, it's pretty simple ( in theory ). In practice, it would be a lot of hard work and that's what most of the terraforming arguments boil down to.
The more conservative members of the scientific community are of the opinion that the whole process would take about 100,000 years from start to finish.
I tend to be regarded by such people as a "hopeless optimist", because I'm of the opinion that with large scale collection of comets from the Kupier belt ( ~ 10,000+ comets ) and enough reflectors ( with a surface area equal to ~10% of the martian surface area ) that we could probably trim that to under 2,000 years and maybe as little as 1,200.
The reason why I mention this is that currently , KS Robinson's Red/Green/Blue Mars series is very popular and unfortunatly, it tends to gloss over a number of important issues. As a point in case, the RGB series assumes that almost all of the necessary volatiles ( except nitrogen ) are already available in the martian regolith.
This is something that we aren't sure about and if it turns out to not be the case, then it's all too likely that the publics current enthusiasm for the concept will turn into an excess of pessimism.
This is an unfortunate aspect of human nature. If people develop unrealistic expectations for something, their disapointment also tends to be excessive.
This was one of the problems with the space race of the 60's. The excess of enthusiasm became an excess of resentment when the bubble finally broke and in many ways, space advocates are still picking up the pieces in terms of the publics negative attitude to the whole subject ( for an alternative 'what might have been', you might want to have a read of Arthur C Clark's 'Prelude to Space'. It's pretty dated by todays standards, but it gives a clear idea of how a lot of people thought that we would go to the moon in the 1950's, and how we would stay there ).
So while I approve in many ways of Zubrin's Mars direct strategy, I remain sceptical of the whole matter simply because I feel that it is better to wait until we know for sure that we can not only do the job, but that next time it will be done right. In other words, I don't think that humans should go to Mars until they are ready to go there with the intention of staying there.
You might be strangling my chicken, but you don't want to know what I'm doing to your hampster.
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