Mathematics – Logic
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....10552b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #10552
Mathematics
Logic
Scientific paper
The thermal evolution of Mars has been studied with parameterized convection models to explain both a crustal evolution consistent with geological and geophysical observations and an early magnetic field in the core. One important aspect of the results is that a high initial mantle temperature of about 2000 K together with a dry mantle rheology (viscosity of about 10{}21 Pas at a reference temperature of 1600 K) is required to explain the observed data. Reducing the initial mantle temperature results in a strong increase of the crust production rate late in the evolution inconsistent with the suggested monotonically declining crust production rate through the Noachian and Hesperian. The non-existence of a present-day magnetic field requires that the core is either solid or totally fluid; no inner core growth is allowed. Using these constraints, models with a viscosity lower than 10{}20 Pas consistent with a wet rheology are unlikely because of efficient cooling of the interior: the calculated present-day core temperatures are lower than the assumed melting temperature of the core material, therefore, inner core growth and present-day dynamo action were likely for those models. The observation of an early strong self-generated magnetic field, finally, places constraints on the initial temperature jump between core and mantle. A superheated core of about hundred Kelvin or more is necessary to initiate thermal convection in the core and consequently dynamo action during the first few hundred million years. Accepting the high initial temperatures after core formation and assuming a rapid core formation process as suggested by geochemical data, it is possible to further constrain the thermal state caused by accretion. The results, based on simple energy equations, suggest a deep magma ocean of about 900 km for a homogeneously accreting Mars.
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