The chemistry of solar system materials: Sun, planets, asteroids, meteorites and dust

Abstract

In this paper we summarize our knowledge of the chemical composition of solar system materials accessible to analysis. In the Sun the three most important rock forming elements Mg, Si and Fe have about the same number of atoms (Mg/SiD1; Fe/SiD0.91); the number of Al atoms is a factor of 10 lower (Al/SiD0.09). Chondritic meteorites have essentially the same chemical signature with some variability, about 20% for Mg/Si, 50% for Al/Si and a factor of two for Fe/Si. These variations can be accounted for by variably mixing components that formed by condensation in a cooling gas of solar composition (Mg-silicates, Ca,Al-rich inclusions, NiFe metal). The bulk Earth composition is within this range and may be considered in a broad sense to be chondritic. The bulk compositions of the other terrestrial planets are less well known. They all have a metal core and basaltic surface rocks. Exceptions are Mercury with too much and the Moon with too little iron for a chondritic bulk composition. Asteroids also seem to have chondritic bulk compositions. S-type asteroids have been confirmed to be the parent bodies of ordinary chondrites. Most of the C-type asteroids appear to represent carbonaceous chondrites. The mm to sub-millimeter sized micrometeorites are debris of asteroids and/or comets. They are largely chondritic in composition but the ratio of cometary to asteroidal material is unclear. If there is a significant fraction of cometary material, comets should have chondritic bulk composition, as approximately inferred from the Giotto data.