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| Titel |
Impact of tidal heating on the onset of convection in Enceladus' ice shell |
| VerfasserIn |
Marie Behounkova, Gabriel Tobie, Gael Choblet, Ondrej Cadek |
| 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 |
250074896
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| Zusammenfassung |
| Observations of Enceladus by the Cassini spacecraft indicated that its south pole is very
active, with jets of water vapor and ice emanating from warm tectonic ridges. Convective
processes in the ice shell are commonly advocated to explain the enhanced activity at the
south pole. The conditions under which convection may occur on Enceladus are, however,
still puzzling. According to the estimation of Barr and McKinnon (2007) based on scaling
laws, convection may initiate in Enceladus’ ice shell only for grain size smaller than 0.3 mm,
which is very small compared to the grain size observed on Earth in polar ice sheets
for similar temperature and stress conditions (2-4mm). Moreover, BÄhounková
et al. (2012) showed that such enhanced activity periods associated with thermal
convection and internal melting should be brief (~ 1 - 10Myrs) and should be
followed by relatively long periods of inactivity (~ 100Myrs), with a probable
cessation of thermal convection. In order to constrain the likelihood and periodicity of
enhanced activity periods, the conditions under which thermal convection may
restart are needed to be investigated. In particular, the goal is to understand how tidal
heating, especially during periods of elevated eccentricity, may influence the onset of
convection. To answer this question, 3D simulations of thermal convection including a
self-consistent computation of tidal dissipation using the code Antigone (BÄhounková et
al., 2010, 2012) were performed, a composite non-Newtonian rheology (Goldsby
and Kohlstedt, 2001) and Maxwell-like rheology mimicking Andrade model were
considered. Our simulations show that the onset of convection may occur in Enceladus’
ice shell only for ice grain size smaller or equal than 0.5Â mm in absence of tidal
heating. Tidal dissipation shifts the critical grain size for convection up to values of
1-1.5 mm. The convection is initiated in the polar region due to enhanced tidal
dissipation in this area and remains in the southern hemisphere as long as the
ocean width is smaller than Δ < 240°. Furthermore, we show that the onset of
convection is associated with internal melting for tidal heating rate larger than
~ 0.5 - 1 -
10-6Wm-3 and that increasing the heating rate above 10-6Wm-3
does not influence anymore the critical grain size for the initiation of convection. |
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