  NASA's Stardust mission returned rocky material from the coma of comet
81P/Wild 2 (pronounced "Vilt 2") to Earth for laboratory study on January 15,
2006. Comet Wild 2 contains volatile ices and likely accreted beyond the orbit
of Neptune. It was expected that the Wild 2 samples would contain abundant
primordial molecular cloud material--interstellar and circumstellar grains.
Instead, the interstellar component of Wild 2 was found to be very minor, and
nearly all of the returned particles formed in broad and diverse regions of the
solar nebula. While some characteristics of the Wild 2 material are similar to
primitive chondrites, its compositional diversity testifies to a very different
origin and evolution history than asteroids. Comet Wild 2 does not exist on a
continuum with known asteroids. Collisional debris from asteroids is mostly
absent in Wild 2, and it likely accreted dust from the outer and inner Solar
System (across the putative gap created by a forming Jupiter) before dispersal
of the solar nebula. Comets are a diverse set of bodies, and Wild 2 may
represent a type of comet that accreted a high fraction of dust processed in
the young Solar System.
