The origin of s-process isotope heterogeneity in the solar
  protoplanetary disk
  Rocky asteroids and planets display nucleosynthetic isotope variations that
are attributed to the heterogeneous distribution of stardust from different
stellar sources in the solar protoplanetary disk. Here we report new high
precision palladium isotope data for six iron meteorite groups, which display
smaller nucleosynthetic isotope variations than the more refractory
neighbouring elements. Based on this observation we present a new model in
which thermal destruction of interstellar medium dust results in an enrichment
of s-process dominated stardust in regions closer to the Sun. We propose that
stardust is depleted in volatile elements due to incomplete condensation of
these elements into dust around asymptotic giant branch (AGB) stars. This led
to the smaller nucleosynthetic variations for Pd reported here and the lack of
such variations for more volatile elements. The smaller magnitude variations
measured in heavier refractory elements suggest that material from
high-metallicity AGB stars dominated stardust in the Solar System. These stars
produce less heavy s-process elements compared to the bulk Solar System
composition.
