An Ice Age JWST inventory of dense molecular cloud ices

TL;DR

This study uses JWST to analyze dense molecular cloud ices, revealing their composition and early chemical processes crucial for understanding star and planet formation.

Contribution

First detailed JWST observations of dense cloud ices, detecting weak and complex molecules, and providing insights into early ice chemistry in star-forming regions.

Findings

Detection of weak ices like $^{13}$CO$_2$, OCN$^-$, and COMs

Modest growth of icy grains indicated by $^{12}$CO$_2$ profile

Ices contribute 2-19% of key element budgets

Abstract

Icy grain mantles are the main reservoir of the volatile elements that link chemical processes in dark, interstellar clouds with the formation of planets and composition of their atmospheres. The initial ice composition is set in the cold, dense parts of molecular clouds, prior to the onset of star formation. With the exquisite sensitivity of JWST, this critical stage of ice evolution is now accessible for detailed study. Here we show the first results of the Early Release Science program "Ice Age" that reveal the rich composition of these dense cloud ices. Weak ices, including, $^{13}$CO$_2$, OCN$^-$, $^{13}$CO, OCS, and COMs functional groups are now detected along two pre-stellar lines of sight. The $^{12}$CO$_2$ ice profile indicates modest growth of the icy grains. Column densities of the major and minor ice species indicate that ices contribute between 2 and 19% of the bulk budgets of the key C, O, N, and S elements. Our results suggest that the formation of simple and complex molecules could begin early in a water-ice rich environment.