Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p33a1011s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P33A-1011
Other
5410 Composition, 5430 Interiors (8147), 5455 Origin And Evolution, 6235 Mercury
Scientific paper
Mercury represents an end-type member of the terrestrial planets with respect to its density and distance from the Sun. The high uncompressed density indicates that Mercury contains a larger proportion of heavier elements such as iron than any other terrestrial planet. The weak intrinsic magnetic field and compressional surface features as observed by Mariner 10 suggest that Mercury is differentiated with most of the iron concentrated in a substantial Fe-rich core. At least an outer core shell should be liquid at the present time, because the magnetic field is probably generated by a self-sustained core dynamo. Depending on the stiffness of the mantle rheology, even small amounts of a light alloying element such as sulfur will prevent a liquid outer core shell from solidification consistent with cosmochemical arguments in favor of a volatile-poor planet. Owing to the incomplete knowledge of the radial mass distribution, however, estimates of core size and mass have to rely on assumptions concerning core and silicate mantle densities based on cosmochemical reasoning. Provided the Mercurian core consists mainly of iron, its radius is expected to be 0.8 times the planet's radius resulting in core mass fractions of up to 70% and bulk iron-to-silicon mass ratios of about 5 times that of CI chondrites. It is less likely, however, that Mercury is almost entirely composed of iron sulfide, as the planet's mean density that is very close to that of FeS may imply[1], since post-accretional vaporisation and/or collisional stripping by giant impacts then should have removed a huge amount of at least 85% of the mass of proto-Mercury subsequently to core formation. The upcoming Mercury missions along with Earth-bound radar observations are expected to provide important constraints on the internal structure, bulk chemical composition, and evolution of Mercury by determining its gravity field, large-scale topography, and tidal and rotational parameters with unprecedented accuracy [e.g., 2]. References [1] Harder, H., and G. Schubert, G. (2001). Sulfur in Mercury's core? Icarus 151, 118-122. [2] Spohn, T., Sohl, F., Wieczerkowski, K., and Conzelmann, V. (2001). The interior structure of Mercury: What we know, what we expect from BepiColombo. Planet. Space Sci. 49, 1561-1570.
Sohl Frank
Spohn Tilman
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