HR: 13:30h
AN: P23A-01    [Abstracts]
TI: Core Composition and the Magnetic Field of Mercury
AU: * Spohn, T
EM: Tilman.Spohn@dlr.de
AF: DLR Institute of Planetary Research, Rutherfordstrasse 2 , Berlin, D-12489 Germany
AU: Breuer, D
EM: Doris.Breuer@dlr.de
AF: DLR Institute of Planetary Research, Rutherfordstrasse 2 , Berlin, D-12489 Germany
AB: The density of Mercury suggests a core of approximately 1800 km radius and a mantle of approximately 600 km thickness. Convection in the mantle is often claimed to be capable of freezing the core over the lifetime of the solar system if the core is nearly pure iron. The thermal history calculations of Stevenson et al. (1983) and Schubert et al. (1988) suggest that about 5 weight-% sulphur are required to lower the core liquidus sufficiently to prevent complete freezing of the core and maintain a significant fluid outer core shell. Other candidates for a light alloying element require similarly large concentrations. The requirement of a significant concentration of volatile elements in the core is likely to be at variance with cosmochemical arguments for a mostly refractory, volatile poor composition of the planet. We have re-addressed the question of the freezing of Mercury's core using parameterized convection models based on the stagnant lid theory of planetary mantle convection. We have compared these results to earlier calculations (Conzelmann and Spohn, 1999) of Hermian mantle convection using a finite-amplitude convection code. We find consistently that the stagnant lid tends to thermally insulate the deep interior and we find mantle and core temperatures significantly larger than those calculated by Stevenson et al. (1983) and Schubert et al. (1988). As a consequence we find fluid outer core shells for reasonable mantle rheology parameters even for compositions with as little as 0.1 weight-% sulphur. Stevenson, D.J., T. Spohn, and G. Schubert. Icarus, 54, 466, 1983. Schubert, G. M.N. Ross, D.J. Stevenson, and T. Spohn, in Mercury, F. Vilas, C.R. Chapman and M.S. Matthews, eds., p.429, 1988. Conzelmann, V. and T. Spohn, Bull. Am. Astr. Soc., 31, 1102, 1999.
DE: 5430 Interiors (8147)
DE: 5440 Magnetic fields and magnetism
DE: 5455 Origin and evolution
DE: 6235 Mercury
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly