Amino acid photostability on the Martian surface

In the framework of international planetary exploration programs, several space missions are planned to search for organics and bio-signatures on Mars. Previous attempts have not detected any organic compounds in the Martian regolith. It is therefore critical to investigate the processes that may affect organic molecules on and below the planet's surface. Laboratory simulations can provide useful data about the reaction pathways of organic material at Mars' surface. We have studied the stability of amino acid thin films against ultraviolet (UV) irradiation and use those data to predict the survival time of these compounds on and in the Martian regolith. We show that thin films of glycine and D-alanine are expected to have half-lives of 22 ± 5 hr and of 3 ± 1 hr, respectively, when irradiated with Mars-like UV flux levels. Modelling shows that the half-lives of the amino acids are extended to the order of 10⁷ years when embedded in regolith. These data suggest that subsurface sampling must be a key component of future missions to Mars dedicated to organic detection.