Sequential giant planet formation initiated by disc substructure (2406.12340v2)

Abstract: Planet formation models are necessary to understand the origins of diverse planetary systems. Circumstellar disc substructures have been proposed as preferred locations of planet formation but a complete formation scenario has not been covered by a single model so far. We aim to study the formation of giant planets facilitated by disc substructure and starting with sub-micron-sized dust. We connect dust coagulation and drift, planetesimal formation, $N$-body gravity, pebble accretion, planet migration, planetary gas accretion and gap opening in one consistent modelling framework. We find rapid formation of multiple gas giants from the initial disc substructure. The migration trap near the substructure allows the formation of cold gas giants. A new pressure maximum is created at the outer edge of the planetary gap, which triggers the next generation of planet formation resulting in a compact chain of giant planets. A high planet formation efficiency is achieved as the first gas giants are effective in preventing dust from drifting further inwards, which preserves materials for planet formation. Sequential planet formation is a promising framework to explain the formation of chains of gas and ice giants.

• The paper introduces a sequential planet formation model driven by disc substructures that facilitate gap opening and subsequent planetesimal growth.
• It employs integrated DustPy and SyMBAp simulations to track dust coagulation, pebble, and gas accretion while exploring turbulent viscosity effects.
• Results demonstrate high efficiency in giant planet formation and highlight how pressure bumps from gaps trigger a cascade of new planet formation.

Sequential Giant Planet Formation Initiated by Disc Substructure

The paper "Sequential giant planet formation initiated by disc substructure" explores a comprehensive model of planet formation, particularly focusing on the role of substructures within protoplanetary discs. The authors, Lau et al., aim to integrate various processes such as dust coagulation, planetesimal formation, pebble accretion, and gas accretion within a unified framework to explain the formation of giant planets, starting from minute dust grains.

Substructure-Induced Planet Formation

Recent observations indicate that circumstellar disc substructures are prevalent and may serve as prime sites for planet formation. This paper explores the dynamics initiated by such substructures, beginning with the accumulation of dust into planetesimals through mechanisms like the streaming instability. A novel aspect of this research is the focus on sequential planet formation whereby gaps carved out by nascent gas giants facilitate further planet formation processes.

Methodological Framework

The paper employs a sophisticated integration of DustPy and SyMBAp, which are advanced simulations for dust evolution and $N$-body interactions, respectively. The model meticulously follows the trajectory from sub-micron dust to fully-formed gas giants while also addressing gap opening by these newly formed planets. DustPy simulates the viscous evolution of gas and dust within the disc, considering factors such as turbulence and temperature profiles, which are critical for realistic simulations of disc environments.

Key processes like pebble accretion and gas accretion are modeled using state-of-the-art prescriptions that reflect current understanding, such as those accounting for energy considerations during envelope accretion phases. The paper also discusses the impact of different turbulent viscosities ($\alpha$ values) on the outcome of planet formation.

Results and Implications

The numerical simulations reveal a two-fold sequence in planet formation: initially, gas giants form rapidly within the disc's substructure, effectively altering the disc's dynamics by opening substantial gaps. Subsequently, pressure bumps formed at the gap's outer edges act as new sites for the next wave of planetesimal formation. This results in a cascading process where each generation of planet formation sets the stage for the next.

A striking observation is the high efficiency of planet formation in such scenarios, particularly with higher $\alpha$ values, which prevent excessive inward drift of the dust, thereby conserving material for future planet formation. This sequential formation model aligns well with the architecture observed in our Solar System, providing a plausible pathway for the development of gas and ice giants.

Theoretical and Practical Implications

This research holds significant implications for both theoretical models and observatory strategies. Theoretically, it proposes a coherent model that integrates disparate processes into a singular narrative of planet formation, driven by observable features in protoplanetary discs. Practically, it suggests new observational targets, particularly in discs with evident substructures that might anticipate the presence or formation of giant planets.

Future Directions

The paper opens avenues for further exploration into the specifics of disc substructure creation, including the potential role of non-planetary mechanisms such as magnetic instabilities or sublimation fronts. Moreover, the model presented here could be extended to include disc dissipation effects, providing a more comprehensive picture of planetary system evolution, aligning theory more closely with observed exoplanet architectures.

In conclusion, the work by Lau et al. represents a significant step towards understanding planet formation as a sequential and ongoing process mediated by disc substructures, offering a viable explanation for the observed diversity and structure within planetary systems.