2011 Interdisciplinary Summer School: Granular Flows

Astrophysical Applications

Patrick Michel, Nice Observatory in France

Surfaces of planets and small bodies of our Solar System are often covered by a layer of granular material that can range from a fine regolith to a gravel-like structure of varying depths. Therefore, the dynamics of granular materials are involved in many events occurring during planetary and small body evolution thus contributing to their geological properties. This lecture will present the observational evidence of the presence of granular materials on solid celestial bodies, the observed surface characteristics and the reason why the understanding of the dynamics of granular materials over a wide range of conditions (gravity, various kinds of stresses…) can help us to interpret the observations and potentially infer the material properties that explain specific surface features.

Understanding the response of granular media to a variety of stresses is also important in the design of anchors and sampling tools for deployment on planetary and small-body surfaces, since the efficiency of anchoring or collecting a sample from the surface of such bodies is highly dependent on their surface properties. In particular, sample-return missions to asteroids have been studied by at least three main space agencies: ESA, NASA, JAXA. Studies of sampling tool design generally assume that the surfaces consist of granular materials; consequently in-depth knowledge of their response to various stresses is required. Projects of such missions will also be briefly presented during this lecture, showing that a good understanding of granular material dynamics is also crucial in the space mission context.