Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.

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Oxygen isotopic heterogeneity in the early Solar System inherited from the protosolar molecular cloud

Science Advances ◽

10.1126/sciadv.aay2724 ◽

2020 ◽

Vol 6 (42) ◽

pp. eaay2724

Author(s):

Alexander N. Krot ◽

Kazuhide Nagashima ◽

James R. Lyons ◽

Jeong-Eun Lee ◽

Martin Bizzarro

Keyword(s):

Solar System ◽

Molecular Cloud ◽

Limited Range ◽

Terrestrial Planets ◽

Carbonaceous Chondrites ◽

The Sun ◽

Early Solar System ◽

Isotopic Heterogeneity ◽

Oxygen Isotopic ◽

O 24

The Sun is 16O-enriched (Δ17O = −28.4 ± 3.6‰) relative to the terrestrial planets, asteroids, and chondrules (−7‰ < Δ17O < 3‰). Ca,Al-rich inclusions (CAIs), the oldest Solar System solids, approach the Sun’s Δ17O. Ultraviolet CO self-shielding resulting in formation of 16O-rich CO and 17,18O-enriched water is the currently favored mechanism invoked to explain the observed range of Δ17O. However, the location of CO self-shielding (molecular cloud or protoplanetary disk) remains unknown. Here we show that CAIs with predominantly low (26Al/27Al)0, <5 × 10−6, exhibit a large inter-CAI range of Δ17O, from −40‰ to −5‰. In contrast, CAIs with the canonical (26Al/27Al)0 of ~5 × 10−5 from unmetamorphosed carbonaceous chondrites have a limited range of Δ17O, −24 ± 2‰. Because CAIs with low (26Al/27Al)0 are thought to have predated the canonical CAIs and formed within first 10,000–20,000 years of the Solar System evolution, these observations suggest oxygen isotopic heterogeneity in the early solar system was inherited from the protosolar molecular cloud.

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Iron isotope evidence for very rapid accretion and differentiation of the proto-Earth

Science Advances ◽

10.1126/sciadv.aay7604 ◽

2020 ◽

Vol 6 (7) ◽

pp. eaay7604 ◽

Cited By ~ 6

Author(s):

Martin Schiller ◽

Martin Bizzarro ◽

Julien Siebert

Keyword(s):

Solar System ◽

Isotope Composition ◽

Terrestrial Planets ◽

Carbonaceous Chondrites ◽

Iron Isotope ◽

System Composition ◽

Solar System Objects ◽

History Of ◽

Isotope Evidence ◽

Enstatite Chondrites

Nucleosynthetic isotope variability among solar system objects provides insights into the accretion history of terrestrial planets. We report on the nucleosynthetic Fe isotope composition (μ54Fe) of various meteorites and show that the only material matching the terrestrial composition is CI (Ivuna-type) carbonaceous chondrites, which represent the bulk solar system composition. All other meteorites, including carbonaceous, ordinary, and enstatite chondrites, record excesses in μ54Fe. This observation is inconsistent with protracted growth of Earth by stochastic collisional accretion, which predicts a μ54Fe value reflecting a mixture of the various meteorite parent bodies. Instead, our results suggest a rapid accretion and differentiation of Earth during the ~5–million year disk lifetime, when the volatile-rich CI-like material is accreted to the proto-Sun via the inner disk.

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Sequestration of Noble Gases by \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\mathrm{H}\,^{+}_{3}$ \end{document} in Protoplanetary Disks and Outer Solar System Composition

The Astrophysical Journal ◽

10.1086/523925 ◽

2008 ◽

Vol 673 (1) ◽

pp. 637-646 ◽

Cited By ~ 16

Author(s):

O. Mousis ◽

F. Pauzat ◽

Y. Ellinger ◽

C. Ceccarelli

Keyword(s):

Solar System ◽

Noble Gases ◽

Protoplanetary Disks ◽

Outer Solar System ◽

System Composition

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GAS-PHASE SEQUESTRATION OF NOBLE GASES IN THE PROTOSOLAR NEBULA: POSSIBLE CONSEQUENCES ON THE OUTER SOLAR SYSTEM COMPOSITION

The Astrophysical Journal ◽

10.1088/0004-637x/777/1/29 ◽

2013 ◽

Vol 777 (1) ◽

pp. 29 ◽

Cited By ~ 22

Author(s):

F. Pauzat ◽

Y. Ellinger ◽

O. Mousis ◽

M. Ali Dib ◽

O. Ozgurel

Keyword(s):

Solar System ◽

Gas Phase ◽

Noble Gases ◽

Outer Solar System ◽

System Composition ◽

Protosolar Nebula

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The origin of inner Solar System water

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2015.0384 ◽

2017 ◽

Vol 375 (2094) ◽

pp. 20150384 ◽

Cited By ~ 18

Author(s):

Conel M. O'D. Alexander

Keyword(s):

Solar System ◽

Classical Model ◽

Terrestrial Planet ◽

Asteroid Belt ◽

Carbonaceous Chondrites ◽

Outer Solar System ◽

Isotopic Compositions ◽

O Isotopes ◽

N Isotopes

Of the potential volatile sources for the terrestrial planets, the CI and CM carbonaceous chondrites are closest to the planets' bulk H and N isotopic compositions. For the Earth, the addition of approximately 2–4 wt% of CI/CM material to a volatile-depleted proto-Earth can explain the abundances of many of the most volatile elements, although some solar-like material is also required. Two dynamical models of terrestrial planet formation predict that the carbonaceous chondrites formed either in the asteroid belt (‘classical’ model) or in the outer Solar System (5–15 AU in the Grand Tack model). To test these models, at present the H isotopes of water are the most promising indicators of formation location because they should have become increasingly D-rich with distance from the Sun. The estimated initial H isotopic compositions of water accreted by the CI, CM, CR and Tagish Lake carbonaceous chondrites were much more D-poor than measured outer Solar System objects. A similar pattern is seen for N isotopes. The D-poor compositions reflect incomplete re-equilibration with H 2 in the inner Solar System, which is also consistent with the O isotopes of chondritic water. On balance, it seems that the carbonaceous chondrites and their water did not form very far out in the disc, almost certainly not beyond the orbit of Saturn when its moons formed (approx. 3–7 AU in the Grand Tack model) and possibly close to where they are found today. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’.

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Potassium isotope anomalies in meteorites inherited from the protosolar molecular cloud

Science Advances ◽

10.1126/sciadv.abd0511 ◽

2020 ◽

Vol 6 (41) ◽

pp. eabd0511 ◽

Cited By ~ 1

Author(s):

Y. Ku ◽

S. B. Jacobsen

Keyword(s):

Solar System ◽

Isotopic Composition ◽

Thermal Processing ◽

Molecular Cloud ◽

Protoplanetary Disk ◽

The Sun ◽

Volatile Elements ◽

Heterogeneous Distribution ◽

Solar System Bodies ◽

K Depletion

Potassium (K) and other moderately volatile elements are depleted in many solar system bodies relative to CI chondrites, which closely match the composition of the Sun. These depletions and associated isotopic fractionations were initially believed to result from thermal processing in the protoplanetary disk, but so far, no correlation between the K depletion and its isotopic composition has been found. Our new high-precision K isotope data correlate with other neutron-rich nuclides (e.g., 64Ni and 54Cr) and suggest that the observed 41K variations have a nucleosynthetic origin. We propose that K isotope anomalies are inherited from an isotopically heterogeneous protosolar molecular cloud, and were preserved in bulk primitive meteorites. Thus, the heterogeneous distribution of both refractory and moderately volatile elements in chondritic meteorites points to a limited radial mixing in the protoplanetary disk.

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Solar Elemental Abundances

Oxford Research Encyclopedia of Planetary Science ◽

10.1093/acrefore/9780190647926.013.145 ◽

2020 ◽

Author(s):

Katharina Lodders

Keyword(s):

Solar System ◽

Chemical Evolution ◽

Molecular Cloud ◽

The Sun ◽

Galactic Chemical Evolution ◽

Dwarf Star ◽

Dwarf Stars ◽

Elemental Abundances ◽

System Composition ◽

Solar Composition

Solar elemental abundances, or solar system elemental abundances, refer to the complement of chemical elements in the entire Solar System. The Sun contains more than 99% of the mass in the solar system and therefore the composition of the Sun is a good proxy for the composition of the overall solar system. The solar system composition can be taken as the overall composition of the molecular cloud within the interstellar medium from which the solar system formed 4.567 billion years ago. Active research areas in astronomy and cosmochemistry model collapse of a molecular cloud of solar composition into a star with a planetary system and the physical and chemical fractionation of the elements during planetary formation and differentiation. The solar system composition is the initial composition from which all solar system objects (the Sun, terrestrial planets, gas giant planets, planetary satellites and moons, asteroids, Kuiper-belt objects, and comets) were derived. Other dwarf stars (with hydrostatic hydrogen-burning in their cores) like the Sun (type G2V dwarf star) within the solar neighborhood have compositions similar to the Sun and the solar system composition. In general, differential comparisons of stellar compositions provide insights about stellar evolution as functions of stellar mass and age and ongoing nucleosynthesis but also about galactic chemical evolution when elemental compositions of stellar populations across the Milky Way Galaxy is considered. Comparisons to solar composition can reveal element destruction (e.g., Li) in the Sun and in other dwarf stars. The comparisons also show element production of, for example, C, N, O, and the heavy elements made by the s-process in low to intermediate mass stars (3–7 solar masses) after these evolved from their dwarf-star stage into red giant stars (where hydrogen and helium burning can occur in shells around their cores). The solar system abundances are and have been a critical test composition for nucleosynthesis models and models of galactic chemical evolution, which aim ultimately to track the production of the elements heavier than hydrogen and helium in the generation of stars that came forth after the Big Bang 13.4 billion years ago.

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