📝 SummarXiv

Abstract

The term Biosphere Substrate is introduced for celestial bodies, like terrestrial planets or big gas giant moons, suitable to sustain full-scale open biosphere after Terraforming. The purpose of the work is to examine the range of parameters for a biosphere substrate. Most importantly, Biosphere Substrate gravity should sustain full-scale open breathable atmosphere dense enough after Terraforming during the lifecycle of Planetary System. Humans can not reproduce in too low gravity, can not restore functionality after long exposure to microgravity. Extremely high gravity is also the limit for complex life forms functioning. Gravity is the main parameter that is the most difficult to change, thus the range of celestial object sizes fitting the Biosphere Substrate definition is examined first. The capability of a celestial body to retain breathable atmosphere during Planetary System lifecycle depends on planetary magnetic field strength, thus plate tectonics is necessary, sufficient satellite is needed for geodynamo. As chemical composition of Biosphere Substrate surface hydrosphere atmosphere can be drastically adjusted in most cases by importing planetesimas material, this factor in most cases does not determine whether a celestial body can become a Biosphere Substrate. But for water worlds where any solid material to build biological bodies and industrial structures can be more than thousand kilometers deep, chemical composition can become an issue. Temperature is another important parameter, as complex life can exist in rather narrow range. For a full-scale open biosphere development, there must be a sufficient source of power. A Biosphere Substrate orbit must be within technically extendable circumstellar habitable zone. For planets with solid crusts, their rotation thus daylength & tilt can be adjusted by hitting asteroids and comets strictly tangentially with high velocities.