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| Titel |
Constraints on planetary habitability from interior modelling |
| VerfasserIn |
Lena Noack, Mareike Godolt, Philip von Paris, Ana-Catalina Plesa, Barbara Stracke, Doris Breuer, Heike Rauer |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080244
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| Zusammenfassung |
| The most interesting planetary bodies outside the Solar System regarding the search for life
are potentially rocky extrasolar planets. Some of them may feature surface conditions that
allow for liquid water, which is the elementary prerequisite for life as we know it. The
amount of greenhouse gases, like e.g. carbon dioxide (CO2), plays an important role for the
determination of the surface temperature, hence the habitability of an extrasolar planet. The
amount of greenhouse gases is strongly influenced by their outgassing from the
interior.
In this study, we investigate under which conditions the planetary interior structure and
dynamics allow for the build-up of planetary atmospheres which may lead to habitable
surface conditions. We investigate the evolution of a secondary atmosphere for Earth-sized
planets with different interior structures (i.e. iron-silicate mixing ratios) by applying a
two-dimensional model of interior dynamics [1], which allows for the calculation of the
production of partial melt [2]. From this, we estimate the amount of CO2 outgassing for
Earth-sized planets with different core and mantle radii after adapting the total CO2
outgassing in 4.5 Gyr for a Venus reference simulation to the present-day atmosphere
of Venus. We furthermore investigate the possible influence of plate tectonics on
outgassing and the likelihood of plate tectonics depending on the interior structure of the
planet.
We find that the size of the iron core has a large impact on the production of partial melt,
hence on the possible outgassing of CO2, which is due to the pressure-dependence of the
melting temperature of silicate rocks: for planets with a large core the planetary mass is larger
than for a planet with a small iron core, leading to larger melting temperatures in the upper
mantle. Therefore only little outgassing from the interior can be expected. However, for the
determination of the outer edge of the habitable zone it is typically assumed that enough
greenhouse gas CO2 is available in the atmosphere to lead to liquid water at the surface –
independent of the interior of the planet [3]. Our results on the other hand suggest that the
outer boundary of the habitable zone may be constrained by the production of partial melt in
the interior for planets with a large iron core and a thin silicate mantle. However, if plate
tectonics initiates, several tens of bars of CO2 can be outgassed in a short time also for
planets with a large iron core. In this case the outer boundary of the habitable zone
would not be limited by outgassing as is the case for stagnant-lid planets. It is,
however, questionable if planets with a very thin mantle are able to initiate plate
tectonics.
References
[1] Hüttig, C. and Stemmer, K. (2008), PEPI, 171(1-4):137-146.
[2] Plesa, A.-C. and Spohn, T. (2012), Transactions of the HLRS 2011, Springer,
551-565.
[3] Kasting, J., Whitmire, D.P. and Reynolds, R.T. (1993), Icarus, 101:108-128. |
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