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
For example, bismuth crystals grow in an interesting way and, like h20 are less dense as a solid than a liquid. At the utterly extreme temperature/pressure environments expereinced in the universe, it isn't hard to believe there are solids out there we can't begin to predict at present. Below are some 3D crystal growths at SEM and macro scales for earth examples
*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
[1]https://www.lpi.usra.edu/meetings/lpsc2004/pdf/1119.pdf
[2]https://www.youtube.com/watch?v=k0YuivnCXhM