arXiv subjects

Stéphane Michoulier

Publications and source records attributed to Stéphane Michoulier.

4 recordsLinked to original sources

arXiv2026

The CO snow line favours strong clumping by the streaming instability in protoplanetary discs with porous grains

Context: The radial drift and fragmentation of small dust grains in protoplanetary discs impedes their growth past centimetre sizes. Several mechanisms have been proposed to overcome these planet formation barriers, such as dust porosity or the streaming instability (SI), which is today regarded as the most promising mechanism to form planetesimals. Aims: Here, we examine whether the conditions for the SI to lead to strong clumping, the first step in planetesimal formation, are realised in protoplanetary discs containing porous grains. Methods: We used results from previous simulations of the evolution of porous grains subjected to growth, fragmentation, compaction and bouncing in protoplanetary discs. In the ensuing disc structures, we determined the regions where the dust-to-gas ratio exceeds the critical value for strong clumping found in simulations of the SI including external turbulence. Results: We find that the conditions for strong clumping are met within the first hundred thousand years in large regions of protoplanetary discs containing porous grains, provided that the CO snow line is taken into account. If the CO snow line is neglected, the conditions are met only very close to the inner disc edge early on, or over large areas well after 200,000 yr.

astro-ph.EP↗

arXiv2024

Compaction during fragmentation and bouncing produces realistic dust grain porosities in protoplanetary discs

Context: In protoplanetary discs, micron-sized dust grows to form millimetre- to centimetre-sized pebbles but encounters several barriers during its evolution. Collisional fragmentation and radial drift impede further dust growth to planetesimal size. Fluffy grains have been hypothesised to solve these problems. While porosity leads to faster grain growth, the implied porosity values obtained from previous simulations were larger than suggested by observations. Aims: In this paper, we study the influence of porosity on dust evolution taking into account growth, bouncing, fragmentation, compaction, rotational disruption and snow lines, in order to understand their impact on dust evolution. Methods: We develop a module for porosity evolution for the 3D Smoothed Particle Hydrodynamics (SPH) code Phantom that accounts for dust growth and fragmentation. This mono-disperse model is integrated into both a 1D code and the 3D code to capture the overall evolution of dust and gas. Results: We show that porosity helps dust growth and leads to the formation of larger solids than when considering compact grains, as predicted by previous work. Our simulations taking into account compaction during fragmentation show that large millimetre grains are still formed, but are 10 to 100 times more compact. Thus, mm sizes with typical filling factors of ~0.1 match the values measured on comets or via polarimetric observations of protoplanetary discs.

astro-ph.EP↗

arXiv2024

Aeolian erosion in protoplanetary discs: How impactful it is on dust evolution?

Context: Many barriers prevent dust to form planetesimals via coagulation in protoplanetary discs, such as bouncing, collisional fragmentation or aeolian erosion. Modelling dust and the different phenomena that can alter its evolution is therefore needed. Multiple solutions have been proposed, but still need to be confirmed. Aims: In this paper, we explore the role aeolian erosion plays in the evolution of dust. Methods: We use a monodisperse model to account for dust growth and fragmentation, implemented in a 1D model to compute the evolution of single grains and a 3D SPH code to compute the global evolution of dust and gas. We test the erosion model in our code and ensured it matches previous results. Results: With a model of disc reproducing observations, we show with both 1D and 3D studies that erosion is not significant during the evolution of dust when we take fragmentation into consideration. With a low-viscosity disc, fragmentation is less of a problem, but grain growth is also less important, preventing the formation of large objects anyway. In dust traps, close to the star, erosion is also not impactful, even when fragmentation is turned off. Conclusions: We show in this paper that aeolian erosion is negligible when radial drift, fragmentation and dust traps are taken into account and does not alter the dust evolution in the disc. However, it can have an impact on later stages, i.e. when the streaming instability forms large clumps close to the star, or when planetesimals are captured.

astro-ph.EP↗

arXiv2023

Dust grain shattering in protoplanetary discs: collisional fragmentation or rotational disruption?

In protoplanetary discs, the coagulation of dust grains into large aggregates still remains poorly understood. Grain porosity appears to be a promising solution to allow the grains to survive and form planetesimals. Furthermore, dust shattering has generally been considered to come only from collisional fragmentation; however, a new process was recently introduced, rotational disruption. We wrote a one-dimensional code that models the growth and porosity evolution of grains as they drift to study their final outcome when the two shattering processes are included. When simulating the evolution of grains in a disc model that reproduces observations, we find that rotational disruption is not negligible compared to the fragmentation and radial drift. Disruption becomes dominant when the turbulence parameter $α\lesssim 5\xtenpow{-4}$, if the radial drift is slow enough. We show that the importance of disruption in the growth history of grains strongly depends on their tensile strength.

astro-ph.EP↗