JWST Maps Interstellar Ice Composition Around Six Protostars in Orion A
Astronomers have used the James Webb Space Telescope to create the first pixel-by-pixel absorption maps of interstellar ice around six Class 0 protostars in the Orion A molecular cloud, resolving structures down to roughly 100 astronomical units. The study analyzed key ice species including water, carbon dioxide, carbon monoxide, and several nitrogen- and sulfur-bearing molecules across a mid-infrared wavelength range. The findings suggest that interstellar ice forms primarily during the prestellar stage and is largely inherited by the protostellar envelope, with implications for understanding the chemical building blocks available during early star and planet formation.
A new study accepted for publication in The Astrophysical Journal presents detailed spatial and chemical mapping of interstellar ices around six Class 0 protostars — HOPS-56, HOPS-60, HOPS-73, HOPS-91, HOPS-96, and HOPS-108 — located in the Orion A molecular cloud. Using JWST's NIRSpec and MIRI MRS instruments across a 4.3–8.1 micrometer wavelength range, researchers constructed the first pixel-by-pixel absorption maps at a spatial resolution of approximately 100 AU for species including ¹³CO₂, OCN⁻, CO, H₂O, NH₄⁺, and H₂CO, with CH₄ and OCS analyzed at continuum peaks. Column densities were derived by fitting observed spectra against laboratory ice analogs, and radiative transfer modeling was used to validate the estimates within protostellar envelopes. The analysis reveals significant variations in ice abundances and distributions among the six sources, with protostellar heating and outflows visibly influencing ice mantles, most dramatically in HOPS-60. The total ice inventory accounts for roughly 90% of observed ice species, consistent with astrochemical models and supporting the hypothesis that ice chemistry is largely set during the cold prestellar phase. The six protostars fall into two distinct groups based on their ice abundances relative to water, which the authors interpret as potentially reflecting evolutionary differences or variations in envelope density and temperature profiles.
What's missing
The sample size of six protostars limits statistical generalizability to other star-forming regions. Long-term implications for planet formation chemistry, such as how this inherited ice inventory survives into protoplanetary disk stages, are not addressed.
What different sources said
- arXiv astro-phCenter
The Colors of Ices: Measuring ice column density through photometry
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