Microgravity experiments on the collisional behavior of Saturnian ring particles

TL;DR

This study presents innovative microgravity experiments on icy and glass particles to understand their collisional behavior, revealing velocity-dependent restitution coefficients and supporting granular flow models relevant to Saturn's rings.

Contribution

Introduces two novel experimental methods in microgravity environments to analyze collisional properties of icy and glass particles, advancing understanding of planetary ring dynamics.

Findings

Mean coefficient of restitution for ice spheres is 0.45.

Granular system follows Haff's law with restitution coefficient 0.64.

Setup is suitable for studying low-velocity collisions in Saturn's rings.

Abstract

In this paper we present results of two novel experimental methods to investigate the collisional behavior of individual macroscopic icy bodies. The experiments reported here were conducted in the microgravity environments of parabolic flights and the Bremen drop tower facility. Using a cryogenic parabolic-flight setup, we were able to capture 41 near-central collisions of 1.5-cm-sized ice spheres at relative velocities between 6 and $22 \mathrm{cm s^{-1}}$. The analysis of the image sequences provides a uniform distribution of coefficients of restitution with a mean value of $\overline{\varepsilon} = 0.45$ and values ranging from $\varepsilon = 0.06$ to 0.84. Additionally, we designed a prototype drop tower experiment for collisions within an ensemble of up to one hundred cm-sized projectiles and performed the first experiments with solid glass beads. We were able to statistically analyze the development of the kinetic energy of the entire system, which can be well explained by assuming a granular `fluid' following Haff's law with a constant coefficient of restitution of $\varepsilon = 0.64$. We could also show that the setup is suitable for studying collisions at velocities of $< 5 \mathrm{mm s^{-1}}$ appropriate for collisions between particles in Saturn's dense main rings.