The photostability of amino acids in space

Organic compounds observed in the interstellar medium and in solar system b odies are of particular importance for revealing the chemistry that may hav e led to life's origin. Among these compounds, amino acids may have played a crucial role since they are basic components of proteins, which are the e ssential constituents of all organisms. We present laboratory studies testi ng the stability of amino acids against ultraviolet (UV) photolysis. Two bi ological and two nonbiological amino acids have been irradiated in frozen A r, N-2, and H2O to simulate conditions in the interstellar gas and on inter stellar grains. The experimental results can be interpreted to indicate tha t amino acids in the gas phase will likely be destroyed during the lifetime of a typical interstellar cloud. In regions with relatively low UV radiati on, amino acids might be present as transient gas-phase species. Their surv ival in interstellar icy grain mantles and the surface layers of comets and planets is strongly limited in the presence of UV irradiation. The rate of destruction is rather insensitive to the amino acid structure and to the i ce matrix. We consider the implications of these results for the survival a nd transfer of amino acids in space environments, and thus their possible a vailability for prebiotic chemistry.