You deserve a 10 for originality! Keep it up.

IMO, it is a matter of a lack of significant atmosphere and a magnetic field to support life (namly retain heat and to keep out space radiation). With a similar atmosphere, the "tropics" of Mars would be more akin to the more temparate zones on Earth.

Well, what the hell. As long as we're into engineering far beyond the current human capacity, we may go the way of Larry Niven and smear jupiter into a ring with more habitable area than we would need for centuries.

Ahem, I am no physicist but I'd guess that a nuclear explosion of that power may slightly harm whatever habitability the planet originally possesed ...

Well, I don't think this is a reasonable idea, but it is possible to alter the orbit of a planet. I have read a scientific paper on the subject. Basically, the point of the paper is that the sun is gradually getter hotter and expanding. Over time (and this is hundreds of millions to billions of years from now), this will threaten the viability of life on Earth. This very long term phenomenon is much more extreme than what we call 'global warming'. Basically, everything on the surface will fry.

Therefore, the habitable zone, the orbital region where water can be liquid will expand outward with the sun beyond the current orbit of the Earth. What the Earth needs to expand its orbit is orbital energy. The greatest possesor of this in the solar system by far is the massive planet Jupiter. Basically, the theory in the paper was that a small body (asteroid or comet, not THAT small) cycling between Earth and Jupiter could transfer the necessary energy through repeated circuits over the next 6 billion years. Of course this is a very long-term prospect. I wonder if anyone will still care about Earth then, if humanity does survive at all.

Anyway, altering an orbit is possible, though not really practicable on timescales shorter than a large fraction of the age of the universe. For Mars, I suggest terraforming instead.

Since humanity has existed a bare million years and is still evolving it is a pretty sure thing that our descendents a million years or so in the future (assuming we have any) will not be anything we would classify as human. If nothing else, genetic engineering will be a big factor.

Well, I for one have seen this idea advocated far too many times. There was a deranged guy who posted on usenet who called himself Archimedes Plutonium that advocated things like this all the time. He wanted to use either nuclear bombs or the "billiard" method to move Mars, Venus and the moon for terraforming purposes. I'm not going to go into it, but it would take trillions of hydrogen bombs to move a planet. It's out of the question.

To move a planet we're not talking about a miniscule bomb like Tsar bomba.

You'll need bombs the size of skyscrapers. It would take hundreds of thousand of space shuttle like lifts to move that much materials to Mars and a million times more uranium enrichment capacity and mining than today.

Any society that could accomplish such would probably be able to improve life prospects down here at far lower cost.

In addition, I see no point in screwing up another planet with humans until we have evolved for a few million years more and eliminated some of the bugs in the current version of homo sapiens.