How well could this work?<p>On the plus side (for plants), the Martian atmosphere is about 95% CO2. Even though the total pressure of the atmosphere is much less than our own, the partial pressure of CO2 is still about 20 times higher (erring a bit on the generous side).<p>On the other hand, Mars is about 1.5 times as far from the sun, so the intensity of sunlight is less than half, and temperatures are correspondingly colder. Then again, if we're going to support human colonists, we probably need a nuclear power source anyway. So let's assume we rig up bright lighting to grow our plants.<p>There's some uncertainty about the soil, but at least some studies suggest that it could support life. There's probably frozen water there, so we'll use the spare heat from our nuclear reactor to melt some.<p>Humans need approximately 30g of Oxygen per hour, which is roughly 1 mole. A fast-photosynthesising plant can produce 30 umol/m2/s. Running the numbers, you'd need 9 square metres of leaf area photosynthesising at that rate per person - assuming it could carry on 24 hours a day. To supply food, you'd need rather more, because not all of the carbon fixed goes into edible parts.<p>This is actually a lot more feasible than I initially thought. You'd probably want to send robots ahead to construct the base and plant the plants, though. And you still have the problem of life support for the journey, which would be several months.