When recording images of the the comet 67P/Churyumov-Gerasimenko, the Rosetta mission has observed a naturally occuring "experiment". Images of the so-called "Aswan" cliff's collapse have been recorded: One in September of 2014 with fissures visible along the overhang, another in June of 2016 after it has fallen into the valley below.
In a Master's thesis, the images are compared and analyzed in order to reconstruct how exactly the collapse occurred. The goal of this is to draw conclusions regarding the material properties such as the tensile strength of the cliff and thus of the comet, as well its formation.
Furthermore, a bachelor thesis deals with the bulk behavior of granular, icy matter. Images from the Mars rover and orbiter regularly show avalanche-like structures and due to the brighter colored fresh surface it is speculated that water ice could be a component of the matter. In view of this, avalanche experiments with ice under different weightlessness conditions were performed in a drop tower campaign to investigate ice itself as a granular material.
In the bachelor thesis the data of the drop tower campaign will be analyzed in terms of angle of repose, velocity and propagation behavior of the avalanches to gain insight into the dynamical behavior of icy granular matter on asteroids and other small bodies.
This is one of the avalanche experiments. The experiment was performed with crushed ice at a gravity of 0.1*g (g=9.81 m/s²). In addition to the video, there are image files of the same experiment. With both, the avalanche can be analyzed in terms of angle of repose, duration and velocity of the avalanche. The other experiments then differ either in the strength of the gravitaton or the shape of the ice particles.
Photo credit: Natalie Müller (TU BS)
Besides real experiments, simulation of aggregates with a variety of particle parameters has a place in this field of research. The discrete element method (DEM) is used to model the interactions of a particle ensemble (~ 1 million particles) and try to draw conclusions to the behaviour of real samples. Macroscopic parameters like the tensile strength are examined on their dependency on microscopic variables like the particle size or attractive force between two particles. The simulation engines used are Project Chrono and LIGGGHTS, while different techniques like the genetic algorithm are employed for the analysis of the results.
