Exobiology and Evolutionary Biology

PI: Paul Johnson

The objective of the proposed work is to unambiguously determine which pathways, direct photolysis and/or radical chemistry, and reaction products result from UV-induced chemical reactions in the subsurface layers of icy planetary surfaces. The proposed research is relevant to all icy planetary environments in which organic chemical synthesis could occur. Of all the energy sources available to drive such chemical reactions in solar system ices, solar photons are the most ubiquitous. Our program will concentrate on photochemical processes in order to maximize the applicability of our results. We will
focus on amino acids (i.e. glycine, phenylalanine, and glutamic acid) as representative organic compounds due to their fundamental importance to terrestrial biology and variation in chemical structure. Organic photochemistry in ice, particularly at low temperatures and pressures, is a largely unexplored subject. One important question is: Will a typical reaction proceed by the same mechanisms, with similar quantum yields, as in recognized processes found in the gas or liquid phase? In this project we will address product formation from: 1) photolysis of amino acid-water ice mixtures to provide an overall picture of the photon induced chemistry; 2) photolysis of amino acids embedded in an inert Ar ice matrix to isolate and identify direct photolysis products; and 3) a series of experiments to identify and isolate reaction products due to OH and amino acid radicals produced by photolysis of water and amino acids mixtures. By using a variety of monochromatic light sources, we will be able to pin-point the nature and evolution of the parent compounds and product formation as a function of incident energy and bulk temperature. The proposed research will contribute to “NASA’s ongoing exploration of our outer stellar neighborhood and the identification of biosignatures for in situ and remote sensing applications.”