During thermal cycling, organisms could live on thermosynthesis, a theoretical mechanism applicable to the origin of life and the early evolution of biological energy conversion. All extraterrestrial ice may be a repository for frozen dead or dormant organisms from earlier stages of evolution. In the presence of a thermal gradient within the ice, organisms might still be harvesting energy from thermosynthesis. Possible habitats for thermosynthesizers can be found throughout the Solar System, particularly in the cold traps on Mercury and the Moon, convecting waters on Mars, the oceans on moons in the outer Solar System, and smaller bodies rotating in the sunlight such as cosmic dust, meteorites, asteroids, and comets. A general strategy for detecting thermosynthetic organisms on Earth is offered, and highlights of current and upcoming robotic exploratory missions relevant to the detection of thermosynthesis are reviewed.