COSMIC-RAY MODIFICATION OF ORGANIC COMETARY MATTER AS SIMULATED BY CYCLOTRON IRRADIATION

Frozen CH4 and CH4/Ar mixtures were irradiated with 18 MeV protons and 17 MeV3He2+ ions at 15 and 77 K in order to simulate the interaction of cosmic rays with solid organic matter in comets. Solids, sealed into cuvettes, represented the interior of comets, those condensed onto a cold finger ice surfaces. C2H2 and C2H4 were the primary volatile products and were converted to C2H6, and heavier hydrocarbons containing up to 28 carbon atoms, by increasing the radiation dose. The release of hydrogen from open ice layers is reflected in a lower H:C ratio and increased carbonization of the residues, as compared to closed targets which yield higher annulated products such as polycyclic aromatic hydrocarbons (PAH).