ISO observations of interstellar ices: Implications for the pristinity of comets Original Research Article

A significant part of the ISO-SWS (Short Wavelength Spectrometer) guaranteed time is devoted to measure infrared spectra toward protostars, in order to probe interstellar ices and molecules. ISO (Infrared Space Observatory) allows to study for the first time the complete inventory of interstellar ices over the entire spectrum between 2.5–45 μm. First ISO data showed the ubiquitous presence of ices in dense clouds which were never seen before, such as CO2 and CH4 ice and provided new insights into the gas to solid ratio of many interstellar molecules. ISO spectra of interstellar gas and dust in comparison with laboratory results and theoretical models constrain gas/grain interactions, temperature and irradiation conditions towards star-forming regions, and consequently their evolution. Well established abundances of interstellar molecules also guide the interpretation of past and future cometary observations. Current ISO results indicate that cometary ices are a mixture of original interstellar material and material that has been processed to some extent in the solar nebula.