A hypothesis for Mercury’s high metal content
Australian Centre for Astrobiology, University of NSW
Last modified: July 29, 2011
Mercury’s apparently-high metal content remains an outstanding problem in studies of the formation of the solar system. The uncompressed density of both Venus and Earth are about 4.4 gm/cm3, whereas that of Mars is about 3.8 gm/cm3, reflecting a lesser metallic component for the latter. The uncompressed density of Mercury, however, appears anomalously high at about 5.3 gm/cm3. Mercury, despite being far smaller than Earth, has a gross density only just below that of our own planet (5.427 gm/cm3 against 5.515 gm/cm3). This has led to a belief that Mercury’s core is most likely an iron-nickel mix comprising about 42 percent of the planet’s overall volume.
Explanations for this have usually revolved around the planet having initially been of a rather greater mass, but been stripped of a larger silicate exterior either through a giant impact by another planet-sized object or else through having its rocky crust largely vaporised by an initially far-hotter proto-Sun.
The intent of this paper is to propose the hypothesis that Mercury may have formed through the agglomeration of material which was itself enriched in its metal content. The hypothesis is based on the idea that small, electrically-conducting objects, exemplified by nickel-iron meteorites, would have a drag force imposed on them through the action of the dissipative eddy (or Foucault) current force as these objects orbited through the intense, highly-turbulent (and therefore high-gradient) magnetic field that may be expected to have surrounded the early Sun as it formed and passed through its T-Tauri stage.
This eddy current mechanism therefore provides another tool that might be invoked by the cosmogonist in attempting to explain the chemical fractionation observed across the solar system, perhaps contributing to the obvious distinction in composition between the terrestrial planets and the jovian or gas-giant planets. The author finally notes that he has been drawn to this problem through nominative determinism.