Symbol Phi
Phi is part of the quantity the equation computes from the expression on the right.
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Why this formula appears here
If no gas can be trusted individually, the natural move is to look for a property of the whole atmosphere. The most general candidate is thermodynamic disequilibrium: life is a persistent chemical engine, so a biosphere should hold its planet’s atmosphere away from the composition it would relax to if all permitted reactions ran to completion. The quantity is the available Gibbs energy — the difference between the free energy of the observed composition and that of its equilibrium state at the same elemental abundances, temperature and pressure: . Krissansen-Totton, Olson and Catling computed this across Earth history and reported values that make the appeal obvious and…
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Symbol G
G is one of the signed contributions combined to compute the quantity on the left.
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Read it with the definitions, units, and assumptions supplied by the article.
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Published contexts (1)
A symbol can carry a different meaning in another article. Each occurrence keeps its own guide and term definitions.
Equation 1 · Origins & Astrobiology
What a Biosignature Has to Rule Out
This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.
If no gas can be trusted individually, the natural move is to look for a property of the whole atmosphere. The most general candidate is thermodynamic disequilibrium: life is a persistent chemical engine, so a biosphere should hold its planet’s atmosphere away from the composition it would relax to if all permitted reactions ran to completion. The quantity is the available Gibbs energy — the difference between the free energy of the observed composition and that of its equilibrium state at the same elemental abundances, temperature and pressure: . Krissansen-Totton, Olson and Catling computed this across Earth history and reported values that make the appeal obvious and…
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