Nebular mixing constrained by the Stardust samples

Using X-ray microprobe analysis of samples from comet Wild 2 returned by the Stardust mission, we determine that the crystalline Fe-bearing silicate fraction in this Jupiter-family comet is greater than 0.5. Assuming this mixture is a composite of crystalline inner solar system material and amorphous cold molecular cloud material, we deduce that more than half of Wild 2 has been processed in the inner solar system. Several models exist that explain the presence of crystalline materials in comets. We explore some of these models in light of our results.