Giant planet formation at the pressure maxima of protoplanetary disks

II. A hybrid accretion scenario

¹ Grupo de Astrofísica Planetaria, Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP, Paseo del Bosque s/n (1900), La Plata, Argentina
e-mail: oguilera@fcaglp.unlp.edu.ar
² Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Santiago, Chile
³ Núcleo Milenio Formación Planetaria (NPF), Pontificia Universidad Católica, Chile
⁴ Department of Astronomy, Eötvös Loránd University, 1117 Budapest, Pázmány Péter sétány 1/A, Hungary
e-mail: Zs.Sandor@astro.elte.hu
⁵ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
⁶ International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland
⁷ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n (1900), La Plata, Argentina

Received: 21 May 2020
Accepted: 9 August 2020

Abstract

Context. Recent high-resolution observations of protoplanetary disks have revealed ring-like structures that can be associated to pressure maxima. Pressure maxima are known to be dust collectors and planet migration traps. The great majority of planet formation studies are based either on the pebble accretion model or on the planetesimal accretion model. However, recent studies proposed hybrid accretion of pebbles and planetesimals as a possible formation mechanism for Jupiter.

Aims. We aim to study the full process of planet formation consisting of dust evolution, planetesimal formation, and planet growth at a pressure maximum in a protoplanetary disk.

Methods. We compute, through numerical simulations, the gas and dust evolution in a protoplanetary disk, including dust growth, fragmentation, radial drift, and particle accumulation at a pressure maximum. The pressure maximum appears due to an assumed viscosity transition at the water ice line. We also consider the formation of planetesimals by streaming instability and the formation of a moon-size embryo that grows into a giant planet by the hybrid accretion of pebbles and planetesimals, all within the pressure maximum.

Results. We find that the pressure maximum is an efficient collector of dust drifting inwards. The condition of planetesimal formation by streaming instability is fulfilled due to the large amount of dust accumulated at the pressure bump. Subsequently, a massive core is quickly formed (in ~10⁴ yr) by the accretion of pebbles. After the pebble isolation mass is reached, the growth of the core slowly continues by the accretion of planetesimals. The energy released by planetesimal accretion delays the onset of runaway gas accretion, allowing a gas giant to form after ~1 Myr of disk evolution. The pressure maximum also acts as a migration trap.

Conclusions. Pressure maxima generated by a viscosity transition at the water ice line are preferential locations for dust traps, planetesimal formation by streaming instability, and planet migration traps. All these conditions allow the fast formation of a giant planet by the hybrid accretion of pebbles and planetesimals.