http://www.planetary.brown.edu/pdfs/3438.pdf

Geologic history of Mars

The detection of strongly magnetized ancient crust on Mars is one of the most surprising outcomes of recent Mars exploration, and provides important insight about the history and nature of the martian core. The iron-rich core probably formed during the hot accretion of Mars approximately 4.5 billion years ago and subsequently cooled at a rate dictated by the overlying mantle. A core dynamo operated much like Earth's current dynamo, but was probably limited in duration to several hundred million years. The early demise of the dynamo could have arisen through a change in the cooling rate of the mantle, or even a switch in convective style that led to mantle heating. Presently, Mars probably has a liquid, conductive outer core and might have a solid inner core like Earth.

Mars' core and magnetism

Crystallization and chemical differentiation of the early Earth were governed by a combination of various processes Within the uncertainties of physical parameters, the two end-member models, equilibrium crystallization and fractional crystallization, are both possible In terms of crystal size, the boundary between these models is ~ 1 mm Analysis of nucleation and crystal growth in the convecting magma ocean suggests that the crystals in the magma ocean are approximately this size The equilibrium model is preferred because it seems to satisfy better the geochemical constraints According to this model, at the early stages, crystallization proceeds from bottom up without any substantial crystal–melt segregation In a vigorously convecting magma ocean, the thermal profile is approximately adiabatic and the crystal fraction decreases gradually with depth The basic physical reason for equilibrium crystallization is a fast convective cooling during which the solid and the liquid phases had a very limited time window for crystal–melt segregation, about 1000 years Chemical differentiation due to crystal–melt segregation is more significant at low pressures corresponding – with large uncertainties – to the upper mantle It is caused by several factors When the temperature drops below liquidus everywhere, the nucleation–growth–dissolution cycle of crystals changes to continuous crystal growth This increases the crystal size to ~ 1 cm indicating the beginning of crystal–melt segregation When the crystal fraction increases to about 60% near the surface, the convective heat transport is controlled by solid-state creep, which is many orders of magnitude slower Crystal–melt segregation occurs via melt percolation, which is consistent with the geochemical constraints Crystallization of the remaining partially molten layers takes about 10 7 –10 9 years This stage merges with the subsequent planetary evolution controlled by mantle convection and radiogenic heating The long lifetime of the shallow magma ocean suggests that this might be the place where liquid iron equilibrates with the mantle before it sinks down to the core

Magma Oceans and Primordial Mantle Differentiation

Fluid Dynamics of a Terrestrial Magma Ocean

http://solarsystem.wustl.edu/wp-content/uploads/2010/06/SF10-accretion.pdf

Chemistry of atmospheres formed during accretion of the Earth and other terrestrial planets

We show that the surface of a planet growing by planetesimal impact is heated over the melting temperature of the surface materials due to the blanketing effect of an impact induced H2O atmosphere with the present H2O abundance of the Earth even when the accretion time is as long as 108 years. Hence, a ‘magma ocean’ covering the entire surface was formed on the Earth and Moon and other terrestrial planets during their formations.

Formation of a ‘magma ocean’ on the terrestrial planets due to the blanketing effect of an impact-induced atmosphere

On the basis of the model proposed by Matsui and Abe, we will show that two major factors — distance from the Sun and the efficiency of retention of accretional energy — control the early evolution of the terrestrial planets. A diagram of accretional energy versus the optical depth of a proto-atmosphere provides a means to follow the evolutionary track of surface temperature of the terrestrial planets and an explanation for why the third planet in our solar system is an ‘aqua’-planet.

Takafumi Matsui

Papers

Formation of a ‘magma ocean’ on the terrestrial planets due to the blanketing effect of an impact-induced atmosphere

Evolutionary tracks of the terrestrial planets