Abundance, distribution, and origin of 60Fe in the solar protoplanetary
  disk
  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/56Fe~6*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 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)*10-9
and conclude that 60Fe was homogeneously distributed among planetary bodies.
This low ratio is consistent with derivation of 60Fe from galactic background
(60Fe/56Fe=2.8*10-7 in the interstellar medium from gamma-ray observations) and
can be reconciled with high 26Al/27Al=5*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 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 3.7 (+2.5/-1.7) Myr after condensation of
calcium-aluminum-rich inclusions (CAIs).
