Determining the UV photostability of organic molecules is key to understanding the recent detection of such molecules on comets. We used in situ spectroscopy measurements of glycine in both argon...Show moreDetermining the UV photostability of organic molecules is key to understanding the recent detection of such molecules on comets. We used in situ spectroscopy measurements of glycine in both argon and water ice to investigate the photolysis reactions of glycine, and determine the dependence of the VUV-photostability of glycine on the thickness of the water matrix at both 10 K and 100 K. We directly observed the photodissociation of glycine into methylamine and carbondioxide inside the argon matrix, and we found compelling evidence that the water matrix provides a protective environment for the glycine against UV dissociation.Show less