The radiation stability of glycine in solid CO2 – In situ laboratory measurements with applications to Mars

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2015-05, Vol.252, p.466-472
• Main Authors: Gerakines, Perry A., Hudson, Reggie L.
• Format: Article
• Language: English
• Subjects: Astrobiology; Cosmochemistry; Destruction; Glycine; Half life; Ices, IR spectroscopy; Mars; Mars surface; Meters; Rate constants; Searching; Space Sciences (General)
• ISSN: 0019-1035; 1090-2643; 1090-2643
• DOI: 10.1016/j.icarus.2015.02.008

•We present data on the radiolytic destruction of glycine diluted in frozen CO2.•Rate constants were measured in situ, without additional sample manipulation.•Destruction rate constants are 20–40 times higher for glycine in CO2 than in H2O.•Half-lives on Mars are less than 100–200Myr at depths of a few meters. The detection of biologically important, organic molecules on Mars is an important goal that may soon be reached. However, the current small number of organic detections at the martian surface may be due to the harsh UV and radiation conditions there. It seems likely that a successful search will require probing the subsurface of Mars, where penetrating cosmic rays and solar energetic particles dominate the radiation environment, with an influence that weakens with depth. Toward the goal of understanding the survival of organic molecules in cold radiation-rich environments on Mars, we present new kinetics data on the radiolytic destruction of glycine diluted in frozen carbon dioxide. Rate constants were measured in situ with infrared spectroscopy, without additional sample manipulation, for irradiations at 25, 50, and 75K with 0.8-MeV protons. The resulting half-lives for glycine in CO2-ice are compared to previous results for glycine in H2O-ice and show that glycine in CO2-ice is much less stable in a radiation environment, with destruction rate constants ∼20–40 times higher than glycine in H2O-ice. Extrapolation of these results to conditions in the martian subsurface results in half-lives estimated to be less than 100–200Myr even at depths of a few meters.