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.

A new apparatus designed to accelerate/decelerate and study the surface impact phenomena of charged aerosols and nanoparticles over a wide range of mass-tocharge (m/z) ratios and final velocities is described. A nanoparticle ion source coupled with a linear electrostatic trap configured as an image charge detection (ICD) mass spectrometer allows determination of the mass-to-charge ratio and the absolute charge and mass of single nanoparticles. A nine-stage linear accelerator/ decelerator is used to fix the final velocity of the nanoparticles, and in the results reported here the coefficient of restitution for polystyrene latex spheres (PSLs) impacting on silicon is measured using ICD techniques. To enable this apparatus to study a wide range of m/z, the data acquisition system uses a transient digitizer interfaced to a field-programmable gate array module that allows real time calculation of m/z and determination of the pulse sequence for the linear accelerator/decelerator. Electrospray ionization of a colloidal suspension of PSL spheres of 510 and 990 nm has been used to demonstrate acceleration and deceleration of charged nanoparticles and the resolution of the apparatus. Measurements of the coefficient of restitution for PSLs on silicon over the range 10-400 m/s are consistent with previous studies.

A novel detector for measuring the post-impact velocities (trajectory and speed) of charged submicrometer particles is presented. A stack of tapered cylindrically symmetric electrodes connected to a set of image charge detection circuits is used in conjunction with an image-charge-sensitive target to measure the incident velocity and scattered trajectories of charged particles following impact with the target. This particle detector is used in conjunction with a mass, charge, and energy-selected source of collimated charged particles. Polystyrene latex spheres were used to characterize the performance of the detector, and examples of scattering trajectories are analyzed to demonstrate detector functionality. Measurements of the coefficient of restitution for 500 nm diameter tin particles are also reported and compared with previous measurements performed with a simpler image-charge detector. Finally, the angular distribution for 500 nm tin particles scattering from highly polished molybdenum at an incident velocity of 150 m/s is reported.

The Enceladus plume is a target of astrobiological interest in planetary science since it may carry signs of extraterrestrial life entrapped in ice grains formed from the subsurface ocean of this moon of Saturn. Fly-by mission concepts have been proposed to perform close investigations of the plume, including detailed in situ measurements of chemical composition with a new generation of mass spectrometer instrumentation. Such a scenario involves high-velocity collisions (typically around 5 km/s or higher) of the instrument with the encountered ice grains. Postimpact processes may include molecular fragmentation, impact ionization, and various subsequent chemical reactions that could alter the original material prior to analysis. In order to simulate Enceladus plume fly through conditions, we are developing an ice grain accelerator and have coupled it to the quadrupole ion trap mass spectrometer (QITMS) developed for flight applications. Our experimental setup enables the creation and acceleration of ice particles with well-defined size, charge, and velocity, which are subsequently directed into the QITMS, where they impact the surface of the mass analyzer and the analysis of postimpact, volatilized molecules takes place. In this work, we performed mass spectral analysis of ice grains of ca. 1.3 μm in diameter, accelerated and impacted at velocities up to 1000 m/s, with an upgrade of the accelerator in progress that will enable velocities up to 5000 m/s. We report the first observations of ice grain impacts measured by the QITMS, which were recorded as brief increases in the abundance of water molecules detected within the instrument.

The impact dynamics of ice grains on surfaces as a function of velocity, including particle breakup and impact ionization, are of intrinsic interest and are critical for the design of future probes to study the ice grain plume around Enceladus. Measurements of the scattering dynamics of ∼700 nm diameter pure water ice grains upon 0.2−2.4 km/s impact with a metal target are reported here. Production of these Enceladus plume grain analogues and their subsequent acceleration to controlled final velocities were performed with an aerosol impact spectrometer. The particle impact and various impact behaviors, including rebound, sticking, particle fragmentation, and impact ionization, were characterized as a function of velocity with an angle-resolved image-charge particle detector. The probability of rebound, sticking, and particle fragmentation was the highest below 400 m/s, between 400 and 800 m/s, and above 800 m/s, respectively. Impact ionization was also observed for impact velocities above 1000 m/s.