Dr. Morgan Miller

Experiments examining the production of Enceladus ice grain analogues and the characterization of their impact phenomena are reported. These measurements make use of a unique single particle accelerator─the aerosol impact spectrometer (AIS)─to extend studies of the impact dynamics of ice grains down to the 0.1–10 μm diameter range relevant to orbital sampling of Enceladus ice grains. Laboratory generation of Enceladus plume grains followed by an examination of their impact dynamics is required to support the interpretation of ice grain orbital sampling in a potential flyby mission concept. In the work reported here, the AIS was used to inject charged water droplets produced in an electrospray ionization source through an aerodynamic lens and into vacuum such that they freeze within 50–200 μs. The ice grains were then accelerated to a controlled final velocity using a linear accelerator (LINAC). The capability of the LINAC to achieve hypervelocity speeds is explored here. The AIS was equipped with the tapered image charge detector, a multielement image charge detector composed of three charge-sensitive rings and the collision analysis target, providing angle-resolved measurements that revealed impact phenomena including rebound, sticking, and fragmentation for ice grain impacts on a molybdenum target. The velocity-dependent trends of these impact phenomena are reported for impacts ranging from 20 to 900 m/s.

Nanoparticle scattering dynamics play a critical role in a wide range of astrophysical, industrial, and ambient environments; however, experimental data to guide theoretical models that predict this behavior are lacking. The experiments reported here examine these phenomena using single mass-selected, charged, submicron solid tin particles covered with an oxide layer of ∼10 nm thickness that are accelerated with varying energies onto a highly polished molybdenum surface. The scattering angle and speed for each backscattering event were measured and analyzed, revealing notable size-dependent trends in the coefficient of restitution and onset of sticking and charge transfer over the range from 150 to 500 nm diameter. The experimental results are interpreted using a mechanical model of the measured impact behavior, extending particle scattering measurements into a new intermediate size range, important for understanding the transport of submicron tin particles. An empirical scaling rule is also presented that normalizes the size-dependent behavior in terms of the ratio of the incident kinetic energy and impact contact area.