Probing dynamical processes in the planet forming region with dust mineralogy

TL;DR

This study uses Herschel PACS spectra and SED modeling to analyze dust composition and grain growth in the protoplanetary disk of GQ Lup, revealing complex mineralogy and potential water ice detection, indicating active dynamical processes.

Contribution

First detection of water ice in a protoplanetary disk with Herschel, showing detailed dust mineralogy and evidence of dynamical heating or collisions.

Findings

Detection of crystalline water ice grains near 63μm.

Radial gradient in silicate dust composition and grain size.

Evidence of disk-wide heating events or planetesimal collisions.

Abstract

We present Herschel Space Observatory PACS spectra of GQ Lup, a protoplanetary disk in the Lupus star-forming region. Through SED fitting from 0.3{\mu}m to 1.3mm, we construct a self-consistent model of this system's temperature and density structures, finding that although it is 3 Myr old, its dust has not settled to the midplane substantially. The disk has a radial gradient in both the silicate dust composition and grain size, with large amorphous grains in the upper layers of the inner disk and an enhancement of submicron, crystalline grains in the outer disk. We detect an excess of emission in the Herschel PACS B2A band near 63{\mu}m and model it with a combination of {\sim}15 to 70{\mu}m crystalline water ice grains with a size distribution consistent with ice recondensation-enhanced grain growth and a mass fraction half of that of our solar system. The combination of crystalline water ice and silicates in the outer disk is suggestive of disk-wide heating events or planetesimal collisions. If confirmed, this would be the first detection of water ice by Herschel.