The ultrathin atmosphere, cold climate (average - 67°F), and consequential lack of the liquid water that is required for life make Mars an inhospitable planet. But by 2100, scientists predict, Mars colonists will say goodbye to their spacesuits, thanks to a geoengineering scheme that puts greenhouse gases to good use. The process, called terraforming, employs robots to mine 130 million tons of fluoride and sulfur deposits from Martian quarries each year and transport them to factories.