The Limits of Organic Life in Planetary Systems (2007) / Chapter Skim
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6 Why Water? Toward More Exotic Habitats
6 Why Water? Toward More Exotic Habitats
Pages 69-79
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From page 69... ...
In water, for example, the temperature must lie between 273 and 373 K at typical pressures, and the dielectric constant and other physical parameters that influence reaction rates are also within specific ranges. Chemical reactions can take place in the gas and solid phases as well, of course.
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From page 70... ...
Water does not support protein folding, because it disrupts hydrogen bonds that stabilize the fold. Indeed, an examination of the chemical literature for examples of work on self-organizing molecules indicates that chemists consciously trying to achieve this outcome rarely use water, precisely because it disrupts noncovalent directional bonding such as hydrogen bonding.
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From page 71... ...
Although the enzyme ribulose bisphosphate carboxylase attempts to manage the problem without biotin, the problematic reactivity of carbon dioxide competes with the problematic reactivity of dioxygen. Even in highly advanced plants, a sizable fraction of the substrate intended to capture carbon dioxide is destroyed through reaction with dioxygen.
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From page 72... ...
For example, Brunner reported that liquid ammonia and hydrocarbons form two phases, where the hydrocarbon chain contains from 1 to 36 CH2 units.5 Different hydrocarbons become miscible with ammonia at different temperatures and pressures. Thus, formation of ammonia-phobic and ammonia-philic phases, analogous to the hydrophobic and hydrophilic phases in water, useful for isolation would be conceivable in liquid ammonia at temperatures well below its boiling point at standard pressures.
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From page 73... ...
Many authors have discussed the possibility of early life on Venus in its acidic environment.9-13 The surface temperature of Venus is approximately 740 K Sagan and Morowitz even considered organisms that float above the hot surface using hydrogen "float bladders" 14 analogous to those found in terran aquatic organisms, although others have raised questions about how to explain the prior evolution of a float bladder that would let an organism control its altitude.a Schulze-Makuch et al.
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From page 74... ...
It is possible to conceive of liquid/liquid phase separation in bulk hydrocarbons that could achieve the isolation necessary for Darwinian evolution. Because of its reactivity, water destroys hydrolytically unstable organic species.
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From page 75... ...
The second is where the temperature rises to a point where organic molecules are no longer stable; for this discussion, 500 K is chosen as that point. If the second radius is smaller than the first, then the gas giant has a habitable zone for life in supercritical dihydrogen.
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From page 76... ...
Supercriticality in an environment does not, in itself, prohibit life. Some terran enzymes are known to be active in supercritical fluids.30-32 Subsequent reviews can be found in Aaltonen and Rantakyla,33 Kamat et al.,34 and Aaltonen.35 Although most of that work concerns supercritical carbon dioxide as the solvent, fluorinated hydrocarbons (HCF3)
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From page 77... ...
It is possible that organic materials formed in the solid ice phase of interstellar materials provided raw materials used for life originating solely on Earth. If so, the deep freeze of ice in the Oort cloud would have been an excellent place to store these, especially the unstable ones, awaiting delivery to a planet.
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From page 78... ...
Therefore, research into the possibility of life in cryogenic solvents needs to begin by making fundamental measurements and establishing a database describing the solubility of organic species in such solvents over a range of pressures and temperatures that are relevant to locales in the solar system. Concepts of life in the gas phase are speculative, but questions related to organic chemistry in ices are experimentally approachable and are components of NASA missions.
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From page 79... ...
Pp. 414-445 in Chemical Synthesis Using Supercritical Fluids (P.G.
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