Chemical Signatures of Embedded Protoplanets in Planet-forming Disks

ALMA has revealed ubiquitous dust gaps in protoplanetary disks, which suggests that planet formation is well underway. Despite this, it remains difficult to unambiguously connect individual substructures with the location and properties of nascent planets. Since embedded planets locally heat the disk, sublimate volatile-rich ices, and even produce gas shocks, molecular line observations can uniquely trace the earliest stages of planet formation. Here, we present the discovery of the most compelling set of planet-induced chemical signatures to date in the giant-planet-hosting HD 169142 disk. Using high-resolution ALMA observations, we detect localized emission from SO and SiS as well as 12CO and 13CO compact emission counterparts that are all spatially coincident with the position of the recently-confirmed HD 169142 b protoplanet. This is the first detection of SiS emission in a disk and implies that this planet is driving sufficiently strong shocks to produce gas-phase SiS. We then discuss recent modeling efforts showing how we can use these chemical signatures to place powerful constraints on the nature of the HD 169142 b planet, including planet mass and the C/O ratio of nearby, planet-feeding gas. We conclude by summarizing ongoing observational follow-up, including an ALMA molecular line survey around the planet location and a deep VLA search for free-free emission associated with ionized gas near the planet. Overall, this discovery shows that observations of shock-tracing molecules provide a novel approach to the detection and characterization of young planets still embedded in their natal disks.