It is cold on Mars. The temperature of the rocks below ground will be close to the average above ground temperature of -80F. If Martians are to live below ground, they will need to heat their homes. Lots of insulation will be needed. Heating systems that use solar energy would make the most sense. The Martian day is nearly the same as on earth. Although the sun on Mars is only one half as bright as on earth (50 watts per square foot), there are no clouds to interrupt the daytime sunlight. Therefore, there should be plenty of heat energy available by collecting sunlight. Long cylinder type solar collectors would be ideal, since they would not need to track the sun's movement across the sky. These systems would use thin channel shaped mirrors which would concentrate the sunlight onto a center glass heat pipe. A fluid, perhaps a water and antifreeze mixture, would be pumped through the pipe to collect the heat and transfer it into a large thermally insulated tank. The tank would act as a large heat energy storage device that would stay warm during the Martian night. The liquid from the tank could then be piped into shelters to heat them. Similar systems might also be used to melt ice, mined below the surface. If geothermal sources could be found, that heat energy could also be used to keep shelters warm and to melt underground ice for water recovery.