The Icy Universe
Freeze-out of the gas phase elements onto cold grains in dense interstellar and circumstellar media builds up ice mantles. Ices (H2O, NH3, CO, CO2, CH3OH, etcetera) are thus a major reservoir for many of the elements. Their vibrational modes are commonly observed in the infrared spectra of Galactic clouds, extragalactic circumnuclear rings, the envelopes and disks surrounding Young Stellar Objects, and solar system objects. I will discuss how observations show that the ice mantles play a key role in the formation of simple molecules, but that the road toward molecular complexity is less well understood. It is often thought that in their voyage from the dense cloud phase through protostellar accretion, ices deliver volatiles, and even the building blocks for life, to planetary surfaces. This view is controversial. Finally, I will show that the ice absorption, scattering, and emission bands can be used to trace the physical history of the cloud and protostellar environment. This will be valuable in the interpretation of future infrared spectroscopic observations with the James Webb Space Telescope and large ground based telescopes.