By G. Jeffrey Taylor and Linda M. V. Martel, Hawai‘i Institute of Geophysics and Planetology
Interstellar space contains dust. Most of it is not made of well-ordered silicate crystals like those in typical planetary rocks. It is made of disordered, amorphous (non-crystalline) smoke particles. The current view of Solar System formation depicts comets forming far out in the Solar System, in the Kuiper belt beyond Neptune. If true, comets ought to be made entirely of silicate smoke particles (plus ice) like those in interstellar space. This region is too cold to provide enough heat to convert the smoke to crystalline minerals. Where did the Wild 2 chondrules come from then?
A reasonable answer, supported by Nakamura and colleagues, is that dust processed at high temperature in the inner part of the solar nebula must have been transported from the inner nebula to the outer, frigid reaches where comets formed.
Diagram from chapter by Nuth et al. (2005) Chondrites and the Protoplanetary Disk, pg. 678.
This is a schematic diagram of the solar nebula as it was still accreting dust to it. Planets have not yet formed. Materials heated near the protosun circulate to the outer Solar System to the cold regions where comets formed, driven by forces originating near the early Sun.
Don Brownlee (University of Washington, Seattle), Principal Investigator of the Stardust mission, calls this the "Grand Radial Express." Astrophysicists and cosmochemists have suggested several mechanisms for transporting materials within and above the nebular disk surrounding the highly-active infant Sun. The Stardust results give experimental evidence that such vigorous transport took place.