Observations of the Icy Universe

TL;DR

This review discusses the detection and analysis of ice features in space, highlighting formation processes, environmental history, and the role of laboratory experiments, with prospects for future infrared observations.

Contribution

It provides a comprehensive comparison of ice abundances and profiles across different cosmic environments, emphasizing stages of ice formation and the impact of energetic processing.

Findings

Distinct ice formation stages identified, separated by CO freeze out.

Ice band profiles serve as probes of thermal history.

Weak evidence for processing of ices by energetic photons and cosmic rays.

Abstract

Freeze-out of the gas phase elements onto cold grains in dense interstellar and circumstellar media builds up ice mantles consisting of molecules that are mostly formed in situ (H2O, NH3, CO2, CO, CH3OH, and more). This review summarizes the detected infrared spectroscopic ice features and compares the abundances across Galactic, extragalactic, and solar system environments. A tremendous amount of information is contained in the ice band profiles. Laboratory experiments play a critical role in the analysis of the observations. Strong evidence is found for distinct ice formation stages, separated by CO freeze out at high densities. The ice bands have proven to be excellent probes of the thermal history of their environment. The evidence for the long-held idea that processing of ices by energetic photons and cosmic rays produces complex molecules is weak. Recent state of the art observations show promise for much progress in this area with planned infrared facilities.