It makes more sense to call it a fractal rather than a pile. In the paper they reference, it is suggested that particles can form fractal like structures through a diffusion limited aggregation process[0]. One very important result in planetary science is the observation by the astronaut Donald Pettit of granular materials aggregating together in microgravity[1]* . In the experiment[2], it appears that some of the resulting structures resemble those formed in a diffusion limited aggregation process.
*It is also worth noting that this experiment was entirely ad-hoc and came about from Don basically just playing around with stuff in microgravity
[0]https://arxiv.org/pdf/1402.7132.pdf