Scientists who study Mars have laid down the program that they can follow. To begin with, they will have to find out whether life has ever existed on the planet Mars in the past. Secondly they will have to make a reliable map of its surface. And finally, they will have to make a list of the gases. Above all, they will have to discover how much nitrogen it possesses, since nitrogen is 4/5 of the air we breathe. They are surprisingly optimistic about raising the temperature on Mars and believe it could be done in 200 years. It would take a bit longer, though, to transform the atmosphere so that human beings could live there. Scientists estimate that this will take 100,000 years.