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| Titel |
On the relative influence of initial H2O and CO2 contents on the primitive surface conditions and evolution of rocky (exo-)planets |
| VerfasserIn |
Arnaud Salvador, Helène Massol, Anne Davaille, Emmanuel Marcq, Éric Chassefière, Philippe Sarda |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151507
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| Publikation (Nr.) |
 EGU/EGU2017-16098.pdf |
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| Zusammenfassung |
| Estimates of initial volatile contents inside planets primitive magma oceans (hereafter « MO
») varies by several orders of magnitude. However, the release of greenhouse gasses such as
H2O and CO2 during cooling and crystallization of the MO will greatly affect the atmosphere
formation, the planet cooling time scale, its surface temperature, and its potential for
water condensation and habitability. We have therefore conducted a systematic
study of the influence of volatile contents on the secular convective cooling and
solidification of a MO in interaction with the outgassed atmosphere. We developed a 1D
model coupling MO dynamics with a convective-radiative atmosphere using either a
grey approximation or k-correlated opacities, with or without clouds. Initial CO2
and H2O contents were varied between 10−3 and 14×10−2 wt%, and from 0.05
to 2.2 times the Earth Ocean current mass (MEO). We considered an Earth-like
planet, with its Sun intensity ranging from half to the present-day value and a solar
distance from 0.63 to 1.30 AU. The atmosphere albedo was varied between 0.2 and
0.8.
All cases shows the same evolution in two main episodes : after (1) a very rapid cooling
stage driven by the MO cooling and crystallization, the planet reaches (2) a quasi-steady state
where subsequent evolution will take billions of years. The surface temperature is
controlled by the balance between the IR outgoing flux, and the heat flux out of the MO
during (1), and the solar flux during (2). At the end of the first regime (hereafter
« ERCS »), the planetary surface can (i) still be molten or partially-molten, (ii)
solid but dry, (iii) solid and covered by a water ocean, depending on the initial
volatile contents, sun characteristics and sun-planet distance. Regimes diagrams
were obtained. There is a critical sun-planet distance Dc below which water will
never condense, whatever the initial volatile content. For distances larger than Dc,
water condensation strongly depends on the relative proportion of CO2 and H2O.
The larger the H2O content, the easier it is to reach the equilibrium water vapor
pressure and therefore to condense water, for the tested range of CO2 contents. At a
given H2O content, too much CO2 precludes the formation of a water ocean by
greenhouse effect. We were able to find a simple scaling to predict the limit of water
condensation as a function of the atmosphere albedo, the sun-planet distance, the sun
characteristics, and the initial MO volatile contents. This allows us to place bounds on
the habitability potential of Venus, and/or recently discovered exo-planets such as
Proxima-b. |
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