Published online by Cambridge University Press: 25 May 2016
The Infrared Space Observatory (ISO) offered us the opportunity to observe celestial bodies from 2.4 to 196 μm, which is of particular interest for comets. We present here spectroscopic observations with ISO of comets C/1995 O1 (Hale-Bopp) and 103P/Hartley 2. Fluorescence emissions of H2O, CO2 and (for comet Hale-Bopp only) CO and CH4 are observed, yielding the production rates of these species. High-resolution spectra of water permit the study of the rotational and spin temperatures of this molecule. In comet Hale-Bopp, the thermal infrared region of the spectra shows specifically, in addition to continuum-like emission, the signatures of crystalline, Mg-rich olivine (forsterite), and signs of crystalline pyroxenes, amorphous silicates and water ice. The presence of crystalline silicates is also suggested in the Jupiter-family comet P/Hartley 2.