Indirect Detection of Forming Protoplanets via Chemical Asymmetries in Disks

TL;DR

This study demonstrates that chemical asymmetries caused by localized heating from forming planets in circumstellar disks can be detected with ALMA, offering a new method to observe planet formation directly.

Contribution

The paper introduces 3D models showing how embedded young planets induce detectable chemical asymmetries in disks, highlighting HCN as a key tracer for planetary heating.

Findings

Chemical asymmetries are detectable in ~10 hours of ALMA observations.

Luminous young planets heat disks enough to desorb molecules like HCN.

Multiple transitions of molecules provide temperature and velocity information.

Abstract

We examine changes in the molecular abundances resulting from increased heating due to a self-luminous planetary companion embedded within a narrow circumstellar disk gap. Using 3D models that include stellar and planetary irradiation, we find that luminous young planets locally heat up the parent circumstellar disk by many tens of Kelvin, resulting in efficient thermal desorption of molecular species that are otherwise locally frozen out. Furthermore, the heating is deposited over large regions of the disk, $\pm5$ AU radially and spanning $\lesssim60^\circ$ azimuthally. From the 3D chemical models, we compute rotational line emission models and full ALMA simulations, and find that the chemical signatures of the young planet are detectable as chemical asymmetries in $\sim10h$ observations. HCN and its isotopologues are particularly clear tracers of planetary heating for the models considered here, and emission from multiple transitions of the same species is detectable, which encodes temperature information in addition to possible velocity information from the spectra itself. We find submillimeter molecular emission will be a useful tool to study gas giant planet formation in situ, especially beyond $R\gtrsim10$ AU.