True terra!

[Dover]

....To terraform Mars, engineers would have to find a way of thickening its atmosphere, whose pressure is a hundredth of that on Earth. In addition, ways will have to be found to heat up the planet. At present its surface temperature can plunge to minus 60C and below.

However, both goals - heating and thickening - could be achieved together, say researchers. One idea is to build a large mirror, many miles in diameter, and place it orbit above Mars. This would then be used to focus the Sun's rays onto a polar icecap, melting it and releasing its frozen carbon dioxide contents. The carbon dioxide would then trigger greenhouse heating.

The alternative would be to construct plants for generating super-greenhouse gases - made of complex combinations of carbon, chlorine and fluorine, and which are thousands of times more effective than carbon dioxide at trapping heat. These would be built at strategic sites across the planet and should also trigger global temperature rises. Thickening the Martian atmosphere would also protect its surface from the ultra-violet radiation that bombards its surface and which would otherwise kill off most Earth-like lifeforms on the planet.

http://www.guardian.co.uk/science/2004/mar/28/spaceexploration.sciencenews



Sounds a lot like what's happening on Earth.
I recall a story several years ago about Russia's giant space mirror created to purportedly reflect the sun down on parts of it's Siberian regions to create "illumination". Anyone remember that? It seemed so strange and science fiction-like at the time, but apparently it's a technology that has been tested. It was reported to have failed, but it certainly is something to ponder...
http://www.encyclopedia.com/doc/1P2-931192.html

http://news.bbc.co.uk/2/hi/science/nature/272103.stm

On edit: Corrected to say the mirror was created to 'illuminate', not to warm the planet, though I don't see how it wouldn't have the affect of warming along with illuminating. It would be like a second sun.

[Richard D]

1. The Mars series . . .

by Kim Stanley Robinson, Red Mars, Green Mars, and Blue Mars go into the potential steps of terraforming of mars in great detail. The science fiction of today is often the reality of tomorrow. Plus they are a great read.

[Statistical]

3. I second this.

Really great books.

Arthur C Clarke said "these books should be required reading for any future colonists".

Still back to the OP to terraform Mars will also require adding energy & mass. Likely by areobreaking icy asteroids in the atmosphere. The process adds heat and gasses to the system.

[NNadir]

2. One needs to consider why Mars has a thin atmosphere in the first place.

It has to do with its mass.

http://mathworld.wolfram.com/MaxwellDistribution.html