Humberto Campins and Christine M. Comfort

Department of Physics and Astronomy, University of Central Florida, Orlando, Florida 32816-2385, USA.

Reference
Campins H and Comfort CM (2014) Solar system: Evaporating asteroid. Nature 505:487–488.
[doi:10.1038/505487a]

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Küppers et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

Reference
Küppers et al. (2014) Localized sources of water vapour on the dwarf planet (1) Ceres. Nature 505:525–527.
[doi:10.1038/nature12918]

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R.K. Mishra and J.N. Goswami
Physical Research Laboratory, Navrangpura, Ahmedabad, 380009;India

The short-lived now-extinct nuclide ⁶⁰Fe, present in the early Solar System, is a unique product of stellar nucleosynthesis. Even though the first hint for its presence in the early Solar System was obtained more than two decades back, a robust value for Solar System Initial (SSI) ⁶⁰Fe/⁵⁶Fe is yet to be established. A combined study of ²⁶Al-²⁶Mg and ⁶⁰Fe-⁶⁰Ni isotope systematics in chondrules from unequilibrated ordinary chondrites of low petrologic type, Semarkona (LL3.0), LEW 86134 (L3.0), and Y 791324 (L3.1), has been conducted to infer the value of SSI ⁶⁰Fe/⁵⁶Fe. Seven of the analyzed chondrules host resolved radiogenic excess in both⁶⁰Ni and ²⁶Mg resulting from in situ decay of the short-lived nuclides ⁶⁰Fe and ²⁶Al, respectively. The initial²⁶Al/²⁷Al values for these chondrules range from (6.9± 5.8)× 10^-6 to (3.01±1.78) ×10^-5 that suggest their formation between 2.1 to 0.6 Ma after CAIs. The initial ⁶⁰Fe/⁵⁶Fe at the time of formation of these chondrules ranges from (3.2±1.3) ×10^-7 to (1.12±0.39) ×10^-6 and show a good correlation with their initial ²⁶Al/²⁷Al values suggesting co-injection of the two short-lived nuclides, ⁶⁰Fe and ²⁶Al, into the protosolar cloud from the same stellar source. Considering ²⁶Al as a reliable early Solar System chronometer, this data set yield a SSI⁶⁰Fe/⁵⁶Fe value of (7.0±1.2) ×10^-7, if we adopt a half-life value of 2.6 Ma for ⁶⁰Fe reported in a recent study. Model stellar nucleosynthesis yields suggest that both a high mass (5-6.5 M_⊙) Asymptotic Giant Branch (AGB) star or a supernova (SN) could be the source of ⁶⁰Fe and ²⁶Al present in the early solar system. A high mass (∼25M_⊙) SN appears more plausible because of the much higher probability of its close association with the protosolar molecular cloud than a high mass AGB star. Such a SN can also account for SSI abundance of²⁶Al and its correlated presence with ⁶⁰Fe in chondrules.

Reference
Mishra RK and Goswami JN (2014) Fe-Ni and Al-Mg isotope records in UOC chondrules: Plausible stellar source of 60Fe and other short-lived nuclides in the early Solar System. Geochimica et Cosmochimica Acta 167:956.
[doi:10.1016/j.gca.2014.01.011]

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John W. Valley, Michael J. Spicuzza and Takayuki Ushikubo

WiscSIMS, Department of Geoscience, University of Wisconsin, 1215 W. Dayton St., Madison, WI, 53706, USA

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Reference
Valley JW, Spicuzza MJ and Ushikubo T (2014) Correlated δ18O and [Ti] in lunar zircons: a terrestrial perspective for magma temperatures and water content on the Moon. Contributions to Mineralogy and Petrology 167:956.
[doi:10.1007/s00410-013-0956-4]

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