Summary:

The James Webb Space Telescope reveals that interstellar grains in a dense cloud have grown to the micron size prior to entering the protostellar phase leading to star formation. Within the vast clouds of gas and dust scattered across our Galaxy, new stars and planetary systems come to life. This journey involves the accumulation of molecular solids on cold dust grains, forming 'icy grains'. In a groundbreaking study, the James Webb Space Telescope (JWST) observed the early stages of this growth in the dense Chamaeleon I cloud, challenging previous assumptions on where and when grain growth occurs. The findings indicate that icy grain growth begins before the protostellar phase, altering the ice band profiles in spectra and triggering a cascade of changes in local microphysics. Grains reach micron sizes, implying that a solid phase mass transfer occurs, leading to a reduction in available surface area for chemistry, and alterations in the penetration and propagation of radiation fields. This analysis of observations from the 'Ice Age' ERS program, led by Melissa McClure of Leiden Observatory, not only sheds light on the intricacies of grain evolution before the birth of stars and planets but also poses challenges for chemical abundance determination due to the deformation of observed profiles.

Article link: https://doi.org/10.1038/s41550-023-02155-x