Antifreeze in the hot core of Orion

Context. Ices are present in comets and in the mantles of interstellar grains. Their chemical composition has been indirectly derived by observing molecules released in the gas phase, when comets approach the sun and when ice mantles are sublimated or destroyed, e.g. in the hot cores present in high-mass, star-forming regions. Comparison of these chemical compositions sheds light on the formation of comets and on the evolution of interstellar matter from the molecular cloud to a protoplanetary disk, and it shows, to first order, a good agreement between the cometary and interstellar abundances. However, a complex O-bearing organic molecule, ethylene glycol (CH2OH)2, seems to depart from this correlation because it was not easily detected in the interstellar medium (Sgr B2) although it proved to be rather abundant with respect to other O-bearing species in comet C/1995 O1 (Hale-Bopp). Ethylene glycol thus appears, together with the closely related molecules glycolaldehyde CH2OHCHO and ethanol CH3CH2OH, as a key species in the comparison of interstellar and cometary ices as well as in any discussion on the formation of cometary matter.