Composition of the Sun and inner solar system
Abstract
The composition of the solar system is essentially that of the Sun. Findings from helioseismology, solar wind particles, and solar neutrino studies find that the Sun's metallicity is greater than that reported by photospheric measurements. Thus, the predicted photospheric Mg/Si is likely wrong.
Chondrites, undifferentiated meteorites and likely building blocks of the planets, differ markedly in their major element compositions from the Earth and likely other terrestrial planets. Isotopic compositions of chondrites and other meteoritic materials demonstrate that the early solar system was not homogeneous. Significantly, Non-Carbonaceous meteorites (NC), and especially the enstatite chondrites, are isotopically similar to the Earth and have been conjectured as coming from solar system regions closer to the Sun (<4 AU) than Carbonaceous Chondrites (CC) and related meteorites. Chondritic abundances of Fe, Mg, Si, and O sum up to 88 and 93 wt%, with Fe contents typically ranging from 1/5 to 1/3 of its total mass, although the uncommon CB, CH and G type chondrites have a factor of 2 or more metal. The amount of iron accreted by a chondritic or terrestrial planetary body is not set by any particular rule; in the nebula, iron grains and other metallic alloys are more strongly influenced by gravitational and electromagnetic sorting forces, as compared to silicates. Terrestrial planets and chondrites are described by the accreted proportions of olivine to pyroxene (Mg/Si ratio) and values for Fe/O, Fe/Si, Fe/Mg, and Fe/Al. The Earth's high metal content (1/3) and Fe/Al (20±2) value document that the inner accretion disk was reduced and enriched in refractory elements (Al). These principles establishes the bulk composition of a planet up to the 98wt% level, with sulfur, a moderately volatile element, adding <1 to a few% to the final total of a volatile-depleted planet. The chondrites and the bulk Earth form an array in Mg/Si - Al/Si that provide critical insight into what might be the average composition of the inner solar system and potentially that of the Sun's interior. We conclude that the early proto-planetary accretion disk had a inwardly increasing gradient in Fe content, was initially dominated by olivine precipitation, and was likely reduced and volatile depleted leading to low sulfur contents in terrestrial planets.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V43D0099M
- Keywords:
-
- 1009 Geochemical modeling;
- GEOCHEMISTRY;
- 1025 Composition of the mantle;
- GEOCHEMISTRY;
- 1028 Composition of meteorites;
- GEOCHEMISTRY;
- 1060 Planetary geochemistry;
- GEOCHEMISTRY