Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6430411 | Earth and Planetary Science Letters | 2012 | 16 Pages |
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 60Fe (t1/2=2.62±0.04 Myr) in chondrites (60Fe/56Feâ¼6Ã10â7), 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 58Fe/54Fe and 60Ni/58Ni 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 60Fe/56Fe ratio of (11.5±2.6)Ã10â9 and conclude that 60Fe was homogeneously distributed among planetary bodies. This low ratio is consistent with derivation of 60Fe from galactic background (60Fe/56Feâ2.8Ã10â7 in the interstellar medium from γ-ray observations) and can be reconciled with high 26Al/27Alâ¼5Ã10â5 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 26Al and poor in 60Fe. We present the first chronological application of the 60Fe-60Ni decay system to establish the time of core formation on Vesta at 3.7â1.7+2.5 Myr after condensation of calcium-aluminum-rich inclusions (CAIs).
⺠We establish the abundance and distribution of 60Fe in different meteorites. ⺠We obtain 60Fe/56Fe ratios at CAI formation. ⺠60Fe and 26Al origins in the early solar system are discussed. ⺠We estimate the time of core formation on Vesta to be â¼4 Myr after CAI formation. 60Fe was a negligible heat source in planetesimals.