SO and SiS Emission Tracing an Embedded Planet and Compact $^{12}$CO and $^{13}$CO Counterparts in the HD 169142 Disk

TL;DR

This study uses high-resolution ALMA data to detect chemical signatures such as SO, SiS, and CO isotopologues in the HD 169142 disk, revealing potential planet-induced shocks and asymmetries linked to planet formation.

Contribution

First detection of SiS emission in a protoplanetary disk, indicating shocks from an embedded planet, and detailed chemical mapping of the HD 169142 disk revealing planet-related asymmetries.

Findings

Detection of SO, SiS, and CO isotopologue emissions near the planet location.

Evidence of shocks and chemical asymmetries driven by an embedded planet.

Azimuthal asymmetry in SO ring suggesting temperature variations.

Abstract

Planets form in dusty, gas-rich disks around young stars, while at the same time, the planet formation process alters the physical and chemical structure of the disk itself. Embedded planets will locally heat the disk and sublimate volatile-rich ices, or in extreme cases, result in shocks that sputter heavy atoms such as Si from dust grains. This should cause chemical asymmetries detectable in molecular gas observations. Using high-angular-resolution ALMA archival data of the HD 169142 disk, we identify compact SO J=8$_8$-7$_7$ and SiS J=19-18 emission coincident with the position of a ${\sim}$2 M$_{\rm{Jup}}$ planet seen as a localized, Keplerian NIR feature within a gas-depleted, annular dust gap at ${\approx}$38 au. The SiS emission is located along an azimuthal arc and has a similar morphology as a known $^{12}$CO kinematic excess. This is the first tentative detection of SiS emission in a protoplanetary disk and suggests that the planet is driving sufficiently strong shocks to produce gas-phase SiS. We also report the discovery of compact $^{12}$CO and $^{13}$CO J=3-2 emission coincident with the planet location. Taken together, a planet-driven outflow provides the best explanation for the properties of the observed chemical asymmetries. We also resolve a bright, azimuthally-asymmetric SO ring at ${\approx}$24 au. While most of this SO emission originates from ice sublimation, its asymmetric distribution implies azimuthal temperature variations driven by a misaligned inner disk or planet-disk interactions. Overall, the HD 169142 disk shows several distinct chemical signatures related to giant planet formation and presents a powerful template for future searches of planet-related chemical asymmetries in protoplanetary disks.