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Planetesimal formation in turbulent protoplanetary disks

Gerosa, Fabiola Antonietta; (2024) Planetesimal formation in turbulent protoplanetary disks. Doctoral thesis (Ph.D), Université Côte d’Azur. Green open access

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Abstract

Planetary systems form from sub-micron dust embedded in a mostly gaseous protoplanetary disk rotating around a young star. Dust has to grow into planetesimals (kilometer-sized objects), considered to be the building blocks of planets. However, the emergence of planetesimals remains one of the major open questions in planet formation theories due to various barriers in the process. The favored solution is to concentrate dust particles into dense clumps that can gravitationally collapse under self-gravity. A key question in this process is the role played by turbulence. Gas in disks is indeed considered to be in a turbulent state, although the origin and intensity of this turbulence are still debated. It is commonly believed that turbulence has a diffusive effect on dust particles, dispersing concentrations and thus impeding the formation of planetesimals. On the other hand, various studies have shown that dust particles can cluster due to coherent structures in the turbulent flow. The resulting overdensities might be excellent candidates for gravitational collapse. Planetesimal formation in turbulent protoplanetary disks is therefore a controversial topic. This thesis addresses this complex problem with the aim of unraveling the properties of turbulence in disks and its impact on dust dynamics and growth. For this purpose, 2D and 3D numerical simulations of dust par- ticles interacting with a turbulent flow in Keplerian rotation are performed. A systematic study is conducted and innovative analysis methods are employed to provide quantitative insights into dust clustering. The key parameter space for each possible outcome of dust evolution in turbulence is identified. In particular, I show that a weakly turbulent flow in Keplerian rotation should not be treated as homogeneous and isotropic. A striking consequence is the formation of dense clusters of dust. Focusing on known disk instabilities, I identify the turbulence characteristics needed to reach significant dust concentrations. These findings suggest that Convective Overstability may be the most effective candidate for this purpose. Finally, moderate turbulence is also able to reduce or completely halt the radial drift of dust. In this thesis, I reveal promising results for dust growth in turbulent protoplanetary disks. I conclude that turbulence can support dust in overcoming the barriers to planetesimal formation.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Planetesimal formation in turbulent protoplanetary disks
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10203712
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