Possible cometary organic compounds as sources of planetary biospheres

Various organic compounds including complex organic compounds have been detected in comets. Cometary organics are supposed to be formed in interstellar dust (ISD) environments. We examined possible formation of bioorganic compounds in ISDs through simulation experiments and compared with that in primitive Earth atmosphere. It was shown that a wide variety of amino acids were formed in simulated ISD environments in the form of precursors. Pyrimidine bases (uracil, cytosine and thymine) were also formed from the possible interstellar media. These results suggest that comets can bring no less types of bioorganics to planets than those formed in primitive Earth atmosphere. Not only Earth, but also other planetary bodies like Mars and Europa received cometary organics during the late heavy bombardment era. They can be included in possible habitable areas whatever primitive planetary atmosphere they had. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved