  Asteroids and other Small Solar System Bodies (SSSBs) are of high general and
scientific interest in many aspects. The origin, formation, and evolution of
our Solar System (and other planetary systems) can be better understood by
analysing the constitution and physical properties of small bodies in the Solar
System. Currently, two space missions (Hayabusa2, OSIRIS-REx) have recently
arrived at their respective targets and will bring a sample of the asteroids
back to Earth. Other small body missions have also been selected by, or
proposed to, space agencies. The threat posed to our planet by near-Earth
objects (NEOs) is also considered at the international level, and this has
prompted dedicated research on possible mitigation techniques. The DART
mission, for example, will test the kinetic impact technique. Even ideas for
industrial exploitation have risen during the last years. Lastly, the origin of
water and life on Earth appears to be connected to asteroids. Hence, future
space mission projects will undoubtedly target some asteroids or other SSSBs.
In all these cases and research topics, specific knowledge of the structure and
mechanical behaviour of the surface as well as the bulk of those celestial
bodies is crucial. In contrast to large telluric planets and dwarf planets, a
large proportion of such small bodies is believed to consist of gravitational
aggregates ('rubble piles') with no -- or low -- internal cohesion, with
varying macro-porosity and surface properties (from smooth regolith covered
terrain, to very rough collection of boulders), and varying topography
(craters, depressions, ridges) [...].
