Bourse de thèse - Effect of thermal cycling and mechanical impacts on the regolith formation

Surfaces of asteroids are covered by a layer of granular material called regolith. Understanding the origin of regoliths and asteroids and other planetary bodies is a central goal in planetary science, because it would provide important information on the creation of the surfaces of these planetary bodies. Two possible physical processes might be capable of producing regolith by damaging rocks: impacts of other spatial bodies that hit surface rocks at speed of several km/s and the thermal cracking and fragmentation.The latter is induced by the mechanical stresses due to large temperature variations between day and night that are present on atmosphere-less bodies (several hundreds of K within a few hours). A study from the Laboratoire Lagrange team suggests that the second process can be very effective. Moreover, images of Bennu, obtained in December 2018 by OSIRIS-REx NASA sample return space mission, show the presence of several boulders that have been broken into parts. For these boulders, the fragments stayed in place instead of being ejected in the surroundings, which supports thermal cracking scenario. The objective of this project is to gather experimental data to distinguish between these two processes and help estimate their respective importance in the Solar System history. Mechanical and thermal tests will be conducted on analog materials specially designed to mimic regolith.