Measurement of the Oxidation state of Fe in the ISM using X-ray
  Absorption Spectroscopy
  The oxidation state of iron in the interstellar medium (ISM) can provide
constraints on the processes that operated on material in the protosolar disk.
We used synchrotron-based X-ray absorption spectra of several mineral standards
and two kinds of primitive extraterrestrial materials to constrain the
oxidation state and mineralogy of the host-phase of ISM Fe as measured by X-ray
observations of Fe-L ISM absorption from the {\em Chandra X-ray Observatory}.
Given the initial oxidation state of the building blocks of the Solar System,
we explore nebular and parent-body processes that eventually led to the
remarkable diversity of oxidation states of primitive Solar System materials.
Oxidation of cometary material appears to have taken place in the nebula,
before incorporation into cometary nuclei, although the mechanism is unknown.
