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Soutenance de Jérémy Sautel

Ségrégation granulaire dans les astéroïdes
When Jul 12, 2021
from 02:30 to 04:30
Where Amphithéâtre Descartes
Contact Name Jérémy Sautel
Attendees Jérémy Sautel
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This thesis focuses on particle size segregation in rubble-pile asteroids, mostly by using numerical methods, but also with an experimental exploration. It is motivated by the fact that some asteroids are not monolithic, but instead consist of a assembly of rocks held together by gravitation, like for instance asteroid Itokawa. One notices an accumulation of big boulders at the surface, with a heterogeneous distribution. Given the mechanical environment of asteroids, size sorting processes are good candidates to explain these patterns.

The first part of the numerical work deals with a simplified problem : simulating 2D circular asteroids undergoing isotropic and periodic expansions. In this case, we observe a radial segregation and we quantify its typical speed and strength, highlighting the strong role played by friction and rotation. We also observe and study an angular segregation, with the big grains gathering into lobes at the surface, like on Itokawa.

Then, we modified the agregate's topology, which led to observing the analogous of radial and angular segregations. This enabled us to quantify the inter-lobes distance. We also studied the segregation process when the asteroid undergoes collisions: the impact velocity and the grains elasticity thus play an important role. Furthermore, we extended our numerical study to the case of 3D spherical asteroids, and observed very interesting dynamics linking radial and angular segregations with the formation of opposed lobes of big grains. This is very significant considering the surface of Itokawa.

Finally, we built a simple experiment dedicated to the study of granular segregation in a central force field.

Keywords:granular matter, asteroids, astrophysics, segregation, simulations.