Thermal Distribution Resulting from Planetary Core Formation by Iron Rain in a Magma Ocean

Details Thermal Distribution Resulting from Planetary Core Formation by Iron Rain in a Magma Ocean Thermal Distribution Resulting from Planetary Core Formation by Iron Rain in a Magma Ocean

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.v13c2047i&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #V13C-2047

Biology

[5205] Planetary Sciences: Astrobiology / Formation Of Stars And Planets, [5724] Planetary Sciences: Fluid Planets / Interiors, [8125] Tectonophysics / Evolution Of The Earth

Scientific paper

It has been long known that the formation of the core transforms gravitational energy into heat and is able to heat up the whole Earth by about 2000 K. However, the distribution of this energy within the Earth is still debated and depends on the core formation process considered. Iron rain in the surface magma ocean is supposed to be the first mechanism of separation for large planets, iron then ponding at the base of the magma ocean [Stevenson 1990]. Time scale of the separation can be estimated from falling velocity of the iron phase, which is estimated by numerical simulation [Ichikawa et al., 2009] as ~ 10cm/s scale with a centimeter- scale iron droplet. Estimation of the thermal structure after the iron-silicate separation requires the development of a planetary-sized model. However, because of the huge disparity of scales between the cm-sized drops and the 1000km thickness of the magma ocean, direct numerical simulation is impossible and we use a parameterizations of the iron rain. The relation between volume flux and volume fraction of iron is the most basic information. It can be incorporated into a planetary scale 1D model if an appropriate estimation is obtained from local scale simulation results. In this study, we made 1D numerical calculations of the whole magma ocean using a parameterization based on direct numerical simulation of a 10cm scale emulsion of iron in liquid silicates. This parameterization of drop velocities was used to study the possibility of large scale overturn of the emulsion by Rayleigh-Taylor instability. Then, we compute the evolution of the thermal structure during the separation of iron phase. The maximum of the temperature is obtained at the boundary between the metal ponds (or the core if the whole planet is liquid) and the silicate. Therefore, the iron pond is thermally stable and the remaining silicate magma ocean is thermally unstable.

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