Iceline Variations Driven by Protoplanetary Disc Gaps

TL;DR

This study models how gaps in protoplanetary discs caused by forming planets alter the disc's thermal structure and shift icelines, impacting planet composition.

Contribution

It provides the first detailed 2D radiative transfer simulations of dust thermal structure variations caused by planet-induced gaps in protoplanetary discs.

Findings

Gaps allow deeper radiation penetration, warming the midplane by up to 16 K in stellar irradiation-dominated regions.

In viscously-heated regions, gaps cool the midplane by up to 100 K.

Icelines can shift by up to 6.5 AU inward or 4.3 AU outward due to gaps.

Abstract

The composition of forming planets is strongly affected by the protoplanetary disc's thermal structure. This thermal structure is predominantly set by dust radiative transfer and viscous (accretional) heating and can be impacted by gaps - regions of low dust and gas density that can occur when planets form. The effect of variations in dust surface density on disc temperature has been poorly understood until now. In this work, we use the radiative transfer code MCMax to model the 2D dust thermal structure with individual gaps corresponding to planets with masses of 0.1 M$_J$ - 5 M$_J$ and orbital radii of 3, 5, and 10 AU. Low dust opacity in the gap allows radiation to penetrate deeper into the disc and warm the midplane by up to 16 K, but only for gaps located in the region of the disc where stellar irradiation is the dominant source of heat (here, a$\gtrsim$4 AU). In viscously-heated regions (a$\lesssim$4 AU), the midplane of the gap is relatively cooler by up to 100 K. Outside of the gap, broad radial oscillations in heating and cooling are present due to changes in disc flaring. These thermal features affect local segregation of volatile elements (H$_2$O, CH$_4$, CO2, CO) between the dust and gas. We find that icelines experience dramatic shifts relative to gapless models: up to 6.5 AU towards the star and 4.3 AU towards the midplane. While quantitative predictions of iceline deviations will require more sophisticated models which include transport and sublimation/condensation kinetics, our results provide evidence that planet-induced iceline variations represent a potential feedback from the planet onto the composition of material it is accreting.