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

IR spectroscopy data are the bases of the present comparative study of cometary and interstellar dust compositions, allowing the vibrational bands of molecular components to be directly compared at IR wavelengths. Significant organic and silicate band profile differences are noted between comets and molecular clouds' interstellar grains; attention is given to the range of observational efforts, such as the determination of comets' formation temperature from the ortho/para ratio of H2O, which may serve to resolve the question as to whether interstellar dust and ices were the bases for cometary formation without alteration.