What is the feasibility of survival on another planet and being self-sustaining? This question is of particular importance for the future of the space conquest and perhaps also for the future of humanity in general [1,2]. The use of in situ resources and different social organizations have been proposed [3–6,12–19] but there is still a poor understanding of the problem’s variables. I show here that a mathematical model can be used to determine the minimum number of settlers and the way of life for survival on another planet, using Mars as the example [6,15]. It is based on the comparison between the time requirements to implement all kinds of human activities for long term survival and the available time of the settlers. An important parameter of the model is called the sharing factor, which allows some reduction of time requirements per individual if, for example, the activity concerns the construction of an object that can be shared by several individuals. For survival on Mars, some assumptions are made for the organization of the settlers and engineering issues [13–15]. The minimum number of settlers has been calculated and the result is 110 individuals. Other assumptions can be made. The proposed method allows assessments and comparisons, opening the debate for the best strategy for survival. If this relatively low number is confirmed, survival on another planet might be easier than expected, provided that the organization of the settlers is appropriate.