Updated solar photospheric abundances are compared with meteoritic abundances. The uncertainties of solar abundances of many trace elements are considerably reduced compared to the 2003 compilation. Some of the solar rare earth elements have now assigned errors of ± 5%, approaching the accuracy of meteorite analyses. The agreement between solar abundances and CI chondrites is further improved. Problematic elements with comparatively large differences between solar and meteoritic abundances are manganese, hafnium, rubidium, gallium, and tungsten. The CI chondrites match solar abundances in refractory lithophile, siderophile, and volatile elements. All other chondrite groups differ from CI chondrites. With analytical uncertainties, there are no obvious fractionations between CI meteorites and solar abundances. Further progress will primarily come from improved solar abundance determinations. The limiting factor in the accuracy of meteorite abundances is the inherent heterogeneity of CI chondrites, primarily the Orgueil meteorite. The interstellar medium (ISM) from which the solar system formed has the same composition as the Sun for volatile and moderately volatile elements within a factor of 2. The more refractory elements of the ISM are depleted from the gas and are concentrated in grains.
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The composition of Mars
Comparing compositional models of the terrestrial planets provides insights into physicochemical processes that produced planet-scale similarities and differences. The widely accepted compositional model for Mars assumes Mn and more refractory elements are in CI chondrite proportions in the planet, including Fe, Mg, and Si, which along with O make up >90% of the mass of Mars. However, recent improvements in our understandings on the composition of the solar photosphere and meteorites challenge the use of CI chondrite as an analog of Mars. Here we present an alternative model composition for Mars that avoids such an assumption and is based on data from Martian meteorites and spacecraft observations. Our modeling method was previously applied to predict the Earth’s composition. The model establishes the absolute abundances of refractory lithophile elements in the bulk silicate Mars (BSM) at 2.26 times higher than that in CI carbonaceous chondrites. Relative to this chondritic composition, Mars has a systematic depletion in moderately volatile lithophile elements as a function of their condensation temperatures. Given this finding, we constrain the abundances of siderophile and chalcophile elements in the bulkMars and its core. The Martian volatility trend is consistent with <7 wt% S in its core, which is significantly lower than that assumed in most core models (i.e., >10 wt% S). Furthermore, the occurrence of ringwoodite at the Martian core-mantle boundary might have contributed to the partitioning of O and H into the Martian core.
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- Award ID(s):
- 1650365
- NSF-PAR ID:
- 10134891
- Date Published:
- Journal Name:
- Geochimica et cosmochimica acta
- Volume:
- 273
- ISSN:
- 0016-7037
- Page Range / eLocation ID:
- 137-162
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/doi:10.1016/j.gca.2020.01.011
