Laboratory Studies of Astronomical Ices: Reaction Chemistry and Spectroscopy

ConspectusScientists have had evidence for molecules in both comets and interstellar space since the 19th and early 20th centuries. Since then, extraterrestrial molecules ranging from simple diatomics to C₇₀ to amino acids have been detected and identified through remote spectroscopy, spacecraft, and sample return missions. These achievements have been made through the efforts of astronomers and laboratory chemists collaborating to identify molecules in a myriad of exotic environments. It is now understood that even in the coldest depths of dense molecular clouds there is a wealth of chemistry to explore, much of it driven by exposure to radiation. As molecular clouds condense to protostellar disks and eventually form new planetary systems, chemical processes continue and evolve. An understanding of these processes is paramount for explaining the compositions of different bodies in our Solar System and may provide insight into the origins of life.In this Account, we describe the work of the Cosmic Ice Laboratory at NASA's Goddard Space Flight Center to characterize the composition of and understand the chemistry occurring in icy bodies in the Solar System and beyond. Our work has touched on a wide range of extraterrestrial environments, including icy interstellar grains, small bodies such as comets and asteroids, and planets and moons. We are especially interested in the chemical and physical changes that occur in ices as a result of thermal changes or exposure to radiation. To this end, we conduct experiments designed to simulate cold extraterrestrial environments and measure physical properties of single- and multicomponent ices. We expose ices to radiation (e.g., MeV protons or keV-MeV electrons) or high-energy (e.g., UV) photons to initiate physical and chemical changes. We conduct experiments using cryo-vacuum chambers equipped with analytical tools and radiation sources to make most of our measurements, including the collection of all spectroscopic data, in situ. When possible and appropriate, we also collect reaction products for further ex situ analysis. The work of the Cosmic Ice Lab provides critical data to astrochemists and others seeking to understand observations, make predictions, and plan future space missions.