Carbon-bearing ices and PAHs in the edge-on protoplanetary disk ESO-Ha 569

The volatile carbon, oxygen, and nitrogen budget of forming planets is set by the inventory of ices and refractory organics carried on dust grains in protoplanetary disks. Connecting this disk-stage volatile reservoir to the compositions of comets, Kuiper Belt objects, icy moons, and exoplanet atmospheres requires direct constraints on where carbon-bearing species are frozen out, how they are mixed with other ices, and how their observable signatures depend on grain growth and vertical disk structure. Edge-on protoplanetary disks provide the required geometry for these measurements: the optically thick midplane obscures the central star, allowing solid-state absorption features to be detected against scattered infrared continuum emission from the inner disk.

We present new JWST NIRSpec IFU and MIRI MRS observations of the highly inclined protoplanetary disk ESO-Hα 569, covering the principal near- and mid-infrared diagnostics of disk ices and refractory organics. We focus on CO and CO₂ as tracers of the volatile carbon reservoir available for incorporation into icy planetesimals; H₂O anchors the total ice content, and PAH emission traces carbon-bearing material in irradiated disk surface layers.

Interpreting these spectra requires three-dimensional radiative transfer modelling, because ice-band depths in highly inclined disks depend not only on abundance, but also on the scattering surface, grain-size distribution, and vertical location of the ice-bearing material. To scale this analysis to the growing JWST sample of edge-on disks, we have developed a neural emulator that reproduces radiative-transfer spectra of highly inclined disks and accelerates inference by a factor of 10⁶.

For ESO-Hα 569, we recover the radial and vertical distributions of CO, CO₂, and H₂O ices, the grain population producing the absorption features, and the origin of the PAH emission. Comparison with HH 48 NE places these results in the context of the emerging JWST sample and links carbon-bearing solids in planet-forming disks to the volatile inventory inherited by comets, TNOs, and exoplanet atmospheres.