Did comets form from unaltered interstellar dust and ices? The evidence from infrared spectroscopy

The compositions of comets and interstellar dust and ices are compared using information now available through infrared spectroscopy. The advantage of this method is that the vibrational bands of molecular components can be directly compared at infrared wavelengths. We find that there are significant differences between comets and interstellar grains in molecular clouds, specifically in the organic and silicate band profiles and in the relative abundances of some molecules. We discuss observations that can help resolve the question of whether comets formed from unaltered interstellar dust and ices.