JWST ice band profiles reveal mixed ice compositions in the HH 48 NE disk

TL;DR

This study uses JWST observations and a new radiative transfer model to analyze ice compositions in the HH 48 NE protoplanetary disk, revealing complex mixtures and implications for planetary formation.

Contribution

Introduces a novel modeling framework to interpret JWST ice band profiles, providing insights into disk ice composition and mixing, including CO trapping and C/O ratios.

Findings

Ices are mainly mixtures with CO trapping in H2O and CO2.

Disk ice composition differs from earlier protostellar stages.

Low ice-phase C/O ratios (~0.1) are inferred across the disk.

Abstract

Planet formation is strongly influenced by the composition and distribution of volatiles within protoplanetary disks. With JWST, it is now possible to obtain direct observational constraints on disk ices, as recently demonstrated by the detection of ice absorption features towards the edge-on HH 48 NE disk as part of the Ice Age Early Release Science program. Here, we introduce a new radiative transfer modeling framework designed to retrieve the composition and mixing status of disk ices using their band profiles, and apply it to interpret the H2O, CO2, and CO ice bands observed towards the HH 48 NE disk. We show that the ices are largely present as mixtures, with strong evidence for CO trapping in both H2O and CO2 ice. The HH 48 NE disk ice composition (pure vs. polar vs. apolar fractions) is markedly different from earlier protostellar stages, implying thermal and/or chemical reprocessing during the formation or evolution of the disk. We infer low ice-phase C/O ratios around 0.1 throughout the disk, and also demonstrate that the mixing and entrapment of disk ices can dramatically affect the radial dependence of the C/O ratio. It is therefore imperative that realistic disk ice compositions are considered when comparing planetary compositions with potential formation scenarios, which will fortunately be possible for an increasing number of disks with JWST.