Chemical footprints of giant planet formation

Role of planet accretion in shaping the C/O ratio of protoplanetary disks^★

¹ European Southern Observatory, Karl-Schwarzschild-Str 2, 85748 Garching, Germany
e-mail: hjiang@eso.org
² Department of Astronomy, Tsinghua University, 30 Shuangqing Rd, Haidian DS 100084, Beijing, PR China
e-mail: wang-y21@mails.tsinghua.edu.cn
³ School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
⁴ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada

Received: 9 April 2023
Accepted: 16 July 2023

Abstract

Context. Protoplanetary disks, the birthplaces of planets, commonly feature bright rings and dark gaps in both continuum and line emission maps. Accreting planets interact with the disk, not only through gravity, but also by changing the local irradiation and elemental abundances, which are essential ingredients for disk chemistry.

Aims. We propose that giant planet accretion can leave chemical footprints in the gas local to the planet, which potentially leads to the spatial coincidence of molecular emissions with the planet in the ALMA observations.

Methods. Through 2D multi-fluid hydrodynamical simulations in Athena++ with built-in sublimation, we simulated the process of an accreting planet locally heating up its vicinity, opening a gas gap in the disk, and creating the conditions for C-photochemistry.

Results. An accreting planet located outside the methane snowline can render the surrounding gas hot enough to sublimate the C-rich organics off pebbles before they are accreted by the planet. This locally elevates the disk gas-phase C/O ratio, providing a potential explanation for the C₂H line-emission rings observed with ALMA. In particular, our findings provide an explanation for the MWC 480 disk, where previous work identified a statistically significant spatial coincidence of line-emission rings inside a continuum gap.

Conclusions. Our findings present a novel view of linking the gas accretion of giant planets and their natal disks through the chemistry signals. This model demonstrates that giant planets can actively shape their forming chemical environment, moving beyond the traditional understanding of the direct mapping of primordial disk chemistry onto planets.