Comet Hale-Bopp, circumstellar dust, and the interstellar medium

The infrared spectrum of comet Hale-Bopp, as observed with the Infrared Spa ce Observatory (ISO), presents astonishing similarities with those of the d usty disks surrounding young stars. The prominent spectral features of crys talline silicates that occur in comets, have been observed in the circumste llar media of young and old stars, yet not in the interstellar medium. We s uggest from the analogy with the young-star spectra that the crystalline na ture of the silicates in comet Hale-Bopp dates from the early evolution of the solar system, and also that an Oort Cloud or Kuiper Belt is presently f orming around young stars observed by ISO.