Polyoxymethylene in Comet Halley

The RPA2-Positive Ion Cluster Composition Analyser on the Giotto spacecraft detected five distinct groups of mass abundance peaks with regular spacing of about 15 amu and masses up to about 105 amu. Starting with the first peak at about 45 amu, these peaks decrease in intensity with increasing mass. Within their half-width they are in good agreement with dissociation products of formaldehyde polymer, also known as polyoxymethylene (POM). POM has been produced in the laboratory at low temperatures by irradiating formaldehyde with bremsstrahlung from 5 MeV electrons and gamma rays from ⁶⁰Co. It is suggested that cosmic radiation formed POM on grains that were aggregated into comet nuclei or formed POM on the surface layers of nuclei in the Oort cloud.