Mass Transfer via Low Velocity Impacts into Regolith

The study of low velocity collisions (<1 m/s) is essential to understand the growth and formation of aggregates in a number of environments in planetary systems. The Collisions Into Dust Experiment (COLLIDE) and Physics of Regolith Impacts in Microgravity Experiment (PRIME) experiments produced observations of mass transfer from regolith onto an impactor at these velocities in microgravity. We have subsequently carried out ground-based experiments in which a cm-scale sphere impacts and rebounds from a bed of granular material in 1-g laboratory conditions at low impact speeds with the aid of a spring. This allows impacts at v<1 m/s and ensures rebound of the impactor, with the spring providing enough force to overcome gravity. Preliminary results from an impact of a brass impactor into sand (200-500 μm) produced a monolayer of granular material onto the impactor, but the grains are not cohesive enough to allow a significant mass transfer under these conditions. Further experiments with a range of regolith properties, impactor composition and surface properties, impact velocities, and atmospheric conditions will be performed in the laboratory to study the effects of each of these properties on the contact transfer of regolith onto the impactor. Further microgravity experiments with PRIME and in a small drop tower are planned to then study bulk mass transfer with conditions informed by the ground-based experiments. Impacts with the COLLIDE and PRIME microgravity experiments showed mass transfer at speeds < 40 cm/s into JSC-1 lunar regolith simulant and quartz sand targets. We will present the free-fall and laboratory results and implications for the collisional evolution of dust, pebbles and boulders in the protoplanetary disk as well as particles in planetary ring systems.