Constraining giant planet formation with synthetic ALMA images of the Solar System’s natal protoplanetary disk

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: bergez@mpia.de
² Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK

Received: 20 October 2021
Accepted: 16 December 2021

Abstract

New ALMA observations of protoplanetary disks allow us to probe planet formation in other planetary systems, giving us new constraints on planet formation processes. Meanwhile, studies of our own Solar System rely on constraints derived in a completely different way. However, it is still unclear what features the Solar System protoplanetary disk could have produced during its gas phase. By running 2D isothermal hydro-simulations used as inputs for a dust evolution model, we derive synthetic images at millimeter wavelengths using the radiative transfer code RADMC3D. We find that the embedded multiple giant planets strongly perturb the radial gas velocities of the disk. These velocity perturbations create traffic jams in the dust, producing over-densities different from the ones created by pressure traps and located away from the planets’ positions in the disk. By deriving the images at λ = 1.3 mm from these dust distributions, we show that very high resolution observations are needed to distinguish the most important features expected in the inner part (<15 AU) of the disk. The traffic jams, observable with a high resolution, further blur the link between the number of gaps and rings in disks and the number of embedded planets. We additionally show that a system capable of producing eccentric planets by scattering events that match the eccentricity distributions in observed exoplanets does not automatically produce bright outer rings at large radii in the disk. This means that high resolution observations of disks of various sizes are needed to distinguish between different giant planet formation scenarios during the disk phase, where the giants form either in the outer regions of the disks or in the inner regions. In the second scenario, the disks do not present planet-related features at large radii. Finally, we find that, even when the dust temperature is determined self-consistently, the dust masses derived observationally might be off by up to a factor of ten compared to the dust contained in our simulations due to the creation of optically thick regions. Our study clearly shows that in addition to the constraints from exoplanets and the Solar System, ALMA has the power to constrain different stages of planet formation already during the first few million years, which corresponds to the gas disk phase.