Detections of trans-Neptunian ice in protoplanetary disks

TL;DR

This study uses Herschel observations and disk modeling to locate and analyze water ice in protoplanetary disks, revealing insights into the formation of comet-like bodies and water delivery to planets.

Contribution

It provides the first detailed analysis of trans-Neptunian ice in protoplanetary disks, linking ice features to disk structure and potential water delivery mechanisms.

Findings

Ice emitting region is beyond 30 AU, similar to a proto-Kuiper belt.

Crystallized water ice exists in colder regions, indicating localized formation.

The 20-50 micron SED shape may reveal the water ice snow line location.

Abstract

We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystalline water ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30AU, consistent with a proto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observations of cold water vapor. The presence of crystallized water ice at a disk location a) colder than its crystallization temperature and b) where it should have been re-amorphized in ~1 Myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UV models and different ice distributions, we suggest that the SED shape from 20 to 50 micron may probe the location of the water ice snow line in the disk upper layers. This project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets.