Power from Below the Ice: Geothermal Energy Generation on Icy Moons Author: Ken Wisian Description: As humanity explores and expands into the outer solar system, practical sources of power will be needed for permanent instillations and colonies. For robotic exploration to date this has meant solar panels or radioactive fission sources. Each of these power sources have significant drawbacks; solar is subject to the inverse square law of decreasing solar irradiance, while fission sources emit radiation that must be protected against with shielding mass and distance. One possibility that has potential for powering instillations on many outer solar system bodies is geothermal generation. This technology has been producing electricity on Earth for more than 100 years and direct use heat for thousands of years. Conventional geothermal systems are a mature technology and one of the cleanest energy sources today. A new paradigm of zero emission, deep closed-loop geothermal systems is in early trails now. Which type of geothermal power system is best applied will depend on the specific geologic setting, economic, environmental and other policy considerations. Fundamentally all that is needed to produce energy in a geothermal sense is an exploitable temperature differential. On many icy bodies this differential would come from the difference between the surface temperature and a subsurface liquid body. Most commercial geothermal power plants work of the difference between ambient surface air temperature (~25°C) and a subsurface fluid temperature of 200 ± 50°C. This examination mostly focuses on the potential of shallow sub-ice oceans that are approximately 175-200°C warmer than the surface of the body at approximately -200°C. For this setting, what is needed is a -200°C shift in the entire temperature cycle of Earth-bound geothermal systems. While there are significant engineering issues to be solved in producing this energy, the potential, particularly on icy bodies is on the order of Megawatts of power generation per well with no imported fuels (radioisotopes) needed.