Telescope Observations of Interstellar and Circumstellar Ices: Successes of and Need for Laboratory Simulations

Abstract

Ices play a key role in the formation of simple and complex molecules in dense molecular clouds and in the envelopes and protoplanetary disks surrounding young stars. Some fraction of the interstellar ices may become building blocks of comets, and thus be delivered to the early Earth. Laboratory simulations have proven to be crucial in the derivation of ice abundances, in quantifying reaction rates on cold grain surfaces, in determining the thermal and energetic processing history of the ices, and in understanding the interaction between the ices and the underlying refractory grain surfaces. In this invited topical paper I will review possible ways forward in improving our knowledge of the composition of the ices, as many signatures in the interstellar spectra are still poorly identified. I will also emphasize the observed importance of thermal processing of the ices (crystallization, segregation), which likely affects the chemistry after the initial dominance of grain surface reactions. Continued laboratory work is warranted in view of the upcoming observational data from, for example, the James Webb Space Telescope (JWST), which is ideally suited for ices studies. For an exhaustive review on this topic I refer to Boogert, Gerakines & Whittet (2015).