Exotic Forms of Life on Other Worlds

The majority of exoplanets discovered to date, and nearly all the other planets and moons in our solar system, differ significantly from the geophysical conditions on Earth. This necessarily means that habitats on other worlds vary substantially from those with which we are familiar. Organic evolution under the different selective pressures in those alien environments may be expected to give rise to forms of life that are exotic by comparison with our own. Many forms of life may lie beyond the reach of light from their central star due to distance or subsurface sequestration, requiring other sources of energy. Life that could float among the clouds in dense atmospheres might assume sizes and morphologies of remarkable dimensions. Some life could be reminiscent of microbial forms on Earth, but remain quiescent in soil or rock until seasonal transitions or the periodic passage of a terminator between frigid darkness and scorching daylight temporarily brings them to life. Cells bounded by amphiphilic membranes stable in hydrocarbon solvents may thrive in the petrochemical seas of worlds too cold for the existence of liquid water. Finally, structural entities capable of self-assembly and energy consumption may populate alien habitats, despite lacking anything like the cellular organization of life on Earth. Exotic forms of life clearly may be found well beyond the limits of any zone deemed habitable merely by the potential to hold water in liquid form.