So now that the Phoenix Land has all but confirmed to us that there's plenty of water on Mars, this will then spark increased interest in colonizing it. So the main obstacles to Mars being habitable are: 1) Low atmospheric pressure 2) Low temperature 3) poisonous atmosphere 4) absence/scarcity of liquid water 5) absence of magnetosphere due to non-molten core Other than those things, Mars doesn't seem like such a bad place. So here are some proposed solutions: Evaporate the icecaps, to liberate CO2 and H2O, which would raise the atmospheric pressure and temperature. Then we could seed the place with photosynthetic bacteria and vegetation that could transform the CO2 into a breathable oxygen atmosphere. To evaporate the icecaps, we could perhaps use a well-placed nuclear explosion to propel some large chunk of rock or ice towards Mars, and drop it on the icecap(s). A suitably large mass could impact with enough kinetic energy to evaporate enough frozen material to warm the planet and build up its atmosphere to suitable pressure levels. The question is, what kind of impact would be optimal for our purposes? What kind of impact would enable us to obtain returns on our efforts the quickest? How much would we want to raise the atmospheric pressure? I presume we would like to make surface conditions as close to Earth-like as possible (STP, and abundant water supply), and in the quickest timeframe possible. What would happen if we attempted to use a nuke to knock one or both of the moons, Phobos and Deimos, out of orbit to collide with the Martian icecaps? Could this be done? Would it contaminate the orbital space with debris and create a severe hazard to spacecraft? Would we be better off using nukes on some chunk(s) of ice from the asteroid belt or from Jupiter's rings, or Saturn's rings, to send this(these) towards Mars? Or would we be better off using nukes directly on the icecaps to melt them? Or should we use microwave lasers to zap and heat the ice chunks to propel them towards Mars? Or should we use microwave lasers to zap the Moons and drop them on Mars? Or should we use microwave lasers to directly heat the icecaps from orbit? Can we engineer extremely hardy and extremely active extremophile bacteria capable of converting a CO2 atmosphere into oxygen in an accelerated amount of time? Could we place a large solar-powered satellite close to the sun, that could generate a magnetic field to deflect a significant portion of the solar wind much before it reached Mars, rather than trying to stop the solar wind near Mars itself? Etc, etc. What would be the best approach to take, to make the planet's surface most Earth-like, in the shortest amount of time?