Synthesis of Molecules by Cosmic Ion Bombardment

The population of known trans-neptunian objects (TNOs) is growing as new members are being detected and further characterized by both visible and near-IR observers. Good evidence exists that the spectra of TNOs are dominated by absorptions of either water or methane ice. The existence of N2, CO and possibly NH#3 ices is also likely. During their lifetimes, these icy bodies experience a weak, but constant energetic ion radiation environment that drives chemical reactions in their surface ices that ultimately result in a non- volatile tholin. To better understand the formation of more complex and less volatile molecules in irradiated ices, we have performed radiation chemical experiments on icy materials at 10 - 100 K. Gas-phase molecules, or molecular mixtures, are frozen in a vacuum chamber and then exposed to a beam of MeV protons to mimic cosmic-ray bombardment. Changes in ice composition are followed in situ with IR spectroscopy after irradiations, and during warming. In this presentation we will focus on the identity of low temperature and thermally stable radiation products in known outer solar system ices. Our results address likely radiation chemical mechanisms, the stability and evolution of species, and the identification of species awaiting detection. This research is funded through NASA's Planetary Atmospheres and Planetary Geology and Geophysics programs.

691.gsfc.nasa.gov/cosmic.ice.lab