A solar stirling engine based on a horizontal selective flat-plate converter is analyzed in this work. A detailed model for the heat losses towards the atmosphere is presented. The engine's output power is maximised numerically. The analysis is based on meteorological data measured at Viking Landers sites during clear sky and dust storm conditions. All the computations were performed for a solar collection area similar in size with that of Mars Pathfinder's Sojourner The efficiency of converting solar energy into mechanical work at noon is as high as 18%. The power provided by the engine is as high as 16 W during autumn and winter. These results suggest that under the Martian environment the performance of properly designed solar Stirling engines is comparable with that of PV cell power systems.