The chemical composition of the Earth

Allègre, Claude J.; Poirier, Jean‐Paul; Humler, E.; Hofmann, Albrecht W.

doi:10.1016/0012-821x(95)00123-t

Cited by 641 publications

(391 citation statements)

References 34 publications

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“…However, after the first several Spitzer disk detections, it became clear that the total accreted mass should be closer to 1% solar by mass (Jura et al, 2007a), representing only the heavy elements. Currently, using the handful of stars for which detailed measurements of at least O, Mg, Si, Ca and Fe are available, the best extrapolation from calcium to total heavy element accretion rate is the bulk terrestrial mass fraction, giving A ≈ 0.016 (Allègre et al, 1995;Zuckerman et al, 2010;Farihi et al, 2012b). Given the utility of the accretion rate diagnostic, it is important to examine when the steadystate equations might be valid, and the implications otherwise.…”

Section: Accretion Rates and Historymentioning

confidence: 99%

Circumstellar debris and pollution at white dwarf stars

Farihi

2016

New Astronomy Reviews

294

265

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Circumstellar disks of planetary debris are now known or suspected to closely orbit hundreds of white dwarf stars. To date, both data and theory support disks that are entirely contained within the preceding giant stellar radii, and hence must have been produced during the white dwarf phase. This picture is strengthened by the signature of material falling onto the pristine stellar surfaces; disks are always detected together with atmospheric heavy elements. The physical link between this debris and the white dwarf host abundances enables unique insight into the bulk chemistry of extrasolar planetary systems via their remnants. This review summarizes the body of evidence supporting dynamically active planetary systems at a large fraction of all white dwarfs, the remnants of first generation, main-sequence planetary systems, and hence provide insight into initial conditions as well as long-term dynamics and evolution.

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Section: Accretion Rates and Historymentioning

confidence: 99%

Circumstellar debris and pollution at white dwarf stars

Farihi

2016

New Astronomy Reviews

294

265

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“…We tested different accretion masses to characterise their effect on the lithium surface abundance due to fingering convection. In these computations, the accreted matter was assumed to have an Earth-like chemical composition ( Allègre et al 1995). Changing the relative abundances of the accreted heavy elements has a very weak effect because their contribution to the mean molecular weight may be slightly different.…”

Section: Effect Of Accretion-induced Fingering Convectionmentioning

confidence: 99%

Accretion of planetary matter and the lithium problem in the 16 Cygni stellar system

Deal

Richard

Vauclair

2015

A&A

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Context. The 16 Cygni system is composed of two solar analogues with similar masses and ages. A red dwarf is in orbit around 16 Cygni A, and 16 Cygni B hosts a giant planet. The abundances of heavy elements are similar in the two stars, but lithium is much more depleted in 16 Cygni B than in 16 Cygni A, by a factor of at least 4.7. Aims. The interest of studying the 16 Cygni system is that the two star have the same age and the same initial composition. The differences currently observed must be due to their different evolution, related to the fact that one of them hosts a planet while the other does not. Methods. We computed models of the two stars that precisely fit the observed seismic frequencies. We used the Toulouse Geneva Evolution Code (TGEC), which includes complete atomic diffusion (including radiative accelerations). We compared the predicted surface abundances with the spectroscopic observations and confirm that another mixing process is needed. We then included the effect of accretion-induced fingering convection. Results. The accretion of planetary matter does not change the metal abundances but leads to lithium destruction, which depends upon the accreted mass. A fraction of the Earth's mass is enough to explain the lithium surface abundances of 16 Cygni B. We also checked the beryllium abundances. Conclusions. In the case of accretion of heavy matter onto stellar surfaces, the accreted heavy elements do not remain in the outer convective zones, but are mixed downwards by fingering convection induced by the unstable μ-gradient. Depending on the accreted mass, this mixing process may transport lithium down to its nuclear destruction layers and lead to an extra lithium depletion at the surface. A fraction of the Earth's mass is enough to explain a lithium ratio of 4.7 in the 16 Cygni system. In this case beryllium is not destroyed. Such a process may be frequent in planet-hosting stars and should be studied in other cases in the future.

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“…Iron can behave as a siderophile (metal-loving), lithophile (rock-loving) and chalcophile (sulfur-loving) element and is ubiquitous in Solar System planetary bodies. On Earth, it is a major element in the core, the mantle and the crust (Allègre et al, 1995;Rudnick and Gao, 2003). In the past decade, the development of high-resolution Multi-Collector InductivelyCoupled-Plasma Mass-Spectrometers (MC-ICP-MS) has allowed measurements of iron isotope composition at high precision (Belshaw et al, 2000;Zhu et al, 2001;Weyer and Schwieters, 2003;Dauphas et al, 2009b;Millet et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Iron isotope fractionation in planetary crusts

Wang

Moynier

Dauphas

et al. 2012

Geochimica et Cosmochimica Acta

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We present new high precision iron isotope data (d 56 Fe vs. IRMM-014 in per mil) for four groups of achondrites: one lunar meteorite, 11 martian meteorites, 32 howardite-eucrite-diogenite meteorites (HEDs), and eight angrites. Angrite meteorites are the only planetary materials, other than Earth/Moon system, significantly enriched in the heavy isotopes of Fe compared to chondrites (by an average of +0.12& in d 56 Fe). While the reason for such fractionation is not completely understood, it might be related to isotopic fractionation by volatilization during accretion or more likely magmatic differentiation in the angrite parent-body. We also report precise data on martian and HED meteorites, yielding an average d 56 Fe of 0.00 ± 0.01&. Stannern-trend eucrites are isotopically heavier by +0.05& in d 56 Fe than other eucrites. We show that this difference can be ascribed to the enrichment of heavy iron isotopes in ilmenite during igneous differentiation. Preferential dissolution of isotopically heavy ilmenite during remelting of eucritic crust could have generated the heavy iron isotope composition of Stannern-trend eucrites. This supports the view that Stannern-trend eucrites are derived from main-group eucrite source magma by assimilation of previously formed asteroidal crust.These new results show that iron isotopes are not only fractionated in terrestrial and lunar basalts, but also in two other differentiated planetary crusts. We suggest that igneous processes might be responsible for the iron isotope variations documented in planetary crusts.

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The chemical composition of the Earth

Cited by 641 publications

References 34 publications

Circumstellar debris and pollution at white dwarf stars

Circumstellar debris and pollution at white dwarf stars

Accretion of planetary matter and the lithium problem in the 16 Cygni stellar system

Iron isotope fractionation in planetary crusts

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