Life has limits that mean that not everything we can imagine is possible, a multidisciplinary team of scientists has argued. The capacity to rule out some forms of life, based on scientific laws, allows us to focus our energies both when it comes to searching for life on other worlds and making it in laboratories. By publishing what they argue are the limits we can know with current information, the team hopes to assist those involved in these two great projects.
The search for extraterrestrial life is currently mostly a search for liquid water. It’s the liquid ocean inside Europa that inspired NASA to build the Europa Clipper, and the historic presence of water on Mars is one of the main reasons it dominates interplanetary research efforts. Yet those not working in the field often protest this focus is too restricted by our Earthly experiences. “Why shouldn’t extraterrestrial life be fundamentally different?” is a common objection.
The new paper only mentions the water question briefly, but it’s an example of what they call the “logic of life” and why some common features are probably necessary. If this logic is accepted, it becomes easier to see why astrobiologists are mostly not too worried about overlooking life that’s too dissimilar to anything on Earth.
For a start, the authors note; “Every organism on Earth operates as a thermodynamic engine because it acquires free energy from the environment and uses it to drive essential biological functions.” It’s unlikely that anything that doesn’t do this could meet any of the competing definitions of life. The laws of thermodynamics mean that lifeforms obeying these principles must create more entropy. Increasing internal entropy means a lifeform’s decay, so at least during its growth stages - when organized biological machinery is synthesized from simpler components - this entropy needs to be exported.
Put simply, any life form needs to give off heat.
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