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Titel |
The thermodynamic drivers of atmospheric chemical disequilibrium and their relationship to habitability |
VerfasserIn |
N. Virgo, E. Simoncini, A. Kleidon |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250066665
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Zusammenfassung |
Lovelock (1965) proposed that the presence of chemical disequilibrium in a planetary
atmosphere could be used to infer the existence of life. This idea has an increasing
relevance to today’s science as we begin to obtain spectroscopic data about exoplanets’
atmospheres.
However, disequilibrium can be driven by abiotic photochemical and geological processes
as well as biological ones, and as a consequence we need to develop theoretical tools that will
allow us to distinguish between these cases. A primary result of our analysis is that the extent
of chemical disequilibrium is uninformative by itself, since an atmosphere far from
equilibrium can be the result of slow processes building up over time rather than rapid
on-going processes. However, if it is possible to estimate the kinetics of a planet’s
atmospheric chemistry then one can infer the amount of power that must be supplied to the
process that drives the disequilibrium. A high power is more indicative of a biological driving
process such as photosynthesis.
Earth’s atmosphere contains both molecular oxygen and methane, supplied continually by
photosynthesis. These react in the atmosphere to form CO2 and water. We show
using a simple model that adding these reactants and removing the products from
the atmosphere requires around 2 Ã 109 W of power. This power is continually
dissipated by the oxidation of methane, and so at least this amount of power must be
supplied as work in order to maintain the disequilibrium. It will be possible to perform
similar calculations for the atmospheres of exoplanets once better data about the
composition and probable kinetics of their atmospheric chemistry becomes available.
A similarly high figure would be very suggestive of the presence of a biosphere. |
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