Abundance, distribution, and origin of Fe-60 in the solar protoplanetary disk

作者：Tang Haolan; Dauphas Nicolas

来源：Earth and Planetary Science Letters, 2012, 359: 248-263.

DOI：10.1016/j.epsl.2012.10.011

• Iron-60
• extinct radionuclide
• meteorites
• mantle
• differentiation
• chronology

Meteorites contain relict decay products of short-lived radionuclides that were present in the protoplanetary disk when asteroids and planets formed. Several studies reported a high abundance of Fe-60 (t(1/2) = 2.62 +/- 0.04 Myr) in chondrites (Fe-60/Fe-56 similar to 6 x 10(-7)), suggesting that planetary materials incorporated fresh products of stellar nucleosynthesis ejected by one or several massive stars that exploded in the vicinity of the newborn Sun. We measured Fe-59/Fe-54 and Ni-60/Ni-58 isotope ratios in whole rocks and constituents of differentiated achondrites (ureilites, aubrites, HEDs, and angrites), unequilibrated ordinary chondrites Semarkona (LL3.0) and NWA 5717 (ungrouped petrologic type 3.05), metal-rich carbonaceous chondrite Gujba (CBa), and several other meteorites (CV, EL H, LL chondrites; IIIAB, IVA, IVB iron meteorites). We derive from these measurements a much lower initial Fe-60/Fe-56 ratio of (11.5 +/- 2.6) x 10(-9) and conclude that Fe-60 was homogeneously distributed among planetary bodies. This low ratio is consistent with derivation of Fe-60 from galactic background (Fe-60/Fe-56 approximate to 2.8 x 10(-7) in the interstellar medium from gamma-ray observations) and can be reconciled with high Al-26/Al-27 similar to 5 x 10(-5) in chondrites if solar material was contaminated through winds by outer layers of one or several massive stars (e.g., a Wolf-Rayet star) rich in Al-26 and poor in Fe-60. We present the first chronological application of the Fe-60-Ni-60 decay system to establish the time of core formation on Vesta at 3.7(-1.7)(+25) Myr after condensation of calcium-aluminum-rich inclusions (CAls). Published by Elsevier B.V.

• 出版日期2012-12-15