 |
| Titel |
Ganymede's core in the Fe-snow regime: The influence of latent heat on the chemical gradient |
| VerfasserIn |
T. Rückriemen, D. Breuer, T. Spohn |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068306
|
|
|
|
|
|
| Zusammenfassung |
| Some years ago it was proposed [1,2] that solidification processes in cores of small planetary
bodies such as Ganymede may significantly differ from the Earth-like core regime. In the
case of Earth iron solidifies at the core center as a result of cooling. Looking at
cores in the low pressure regime (- 6 to 10 GPa) the iron will rather solidify at the
core-mantle boundary. This difference originates from negative slopes of the melting
curve of iron-rich Fe-FeS alloys in the low pressure range [3,4]. Since the iron is
gravitationally unstable it will sink down towards deeper core regions, where it
will remelt again due to higher temperatures. The result is a chemical gradient
evolving across the core regions, in which iron precipitates. The chemical gradient may
have influence on the generation of magnetic fields in such small planetary bodies.
On the one hand it affects the ability of core cooling and on the other hand the
process of snowing iron could serve as an own mechanism for generating magnetic
fields.
We investigate the thermal evolution of Ganymede’s core in the Fe-snow regime. The model
accounts for the solidification of iron, where we assume thermo-chemical equilibrium, and
the subsequent redistribution of iron to deeper core regions. We focus on the effect of latent
heat associated with freezing and melting processes, which has so far been neglected in
earlier models [1]. Own previous studies showed that heat transport by convection may not be
feasible in the Fe-snow regime due to the large chemical gradients. Thus we consider the
two extreme cases of conductive as well as convective heat transport resulting in a
conductive and adiabatic temperature profile, respectively. We find that for both
temperature profiles the effect of latent heat reduces the chemical gradient. But
nevertheless the chemical gradient is still large enough to impede thermal convection.
Looking at the timescales of the Fe-snow regime until an inner core starts to grow, all
models tested here need considerably more time than those models evaluated in
[1].
References
[1]Â Â Â S. Hauck II, J. Aurnou, and A. Dombard, Journal of Geophysical Research, vol. 111, no.
E9, p. E09008, 2006.
[2]Â Â Â Q. Williams, Earth and Planetary Science Letters, vol. 284, no. 3, pp. 564–569, 2009.
[3]Â Â Â Y. Fei, C.M. Bertka, L.W. Finger, Science, vol. 275 no. 5306, p. 1621–1623,1997.
[4]Â Â Â Y. Fei, J. Li., C.M. Bertka, and C.T. Prewitt, American Mineralogist, vol. 85, no. 11-12,
p. 1830–1833, 2000. |
|
|
|
|
|
|