A newly developed experimental set up to simulate icy moons weathering by micro-meteoroid hyper-velocity impacts

The JUICE (ESA) and Europa Clipper (NASA) missions will study the Jovian system and investigate the habitability of the Jovian moons. The focus of both missions is to characterize the conditions that may have led to the emergence of a habitable environment for life as we know it in the interior of Ganymede, Europa and Callisto. To this end, these missions will explore and investigate the icy moons exospheres, their surfaces and use this characterization to draw conclusions on possible global, sub-surface oceans.

Understanding the physical and chemical properties of the area where ocean material may be upwelling through the surface is key to constraining the ocean’s composition. However, the harsh weathering of the icy moons’ surfaces by the Jovian magnetospheric radiation and by the hyper-velocity impacts of micro-meteoroids modifies the exposed surface material, complicating our understanding of the endogenic material’s evolution. 

The activity to be presented focuses on micro-meteoroids as ice weathering agents in the Jovian system - 
The main goal is to understand how micro-meteoroids impacts alter the icy moon’s surface and contribute to the formation of volatiles injected into the moon’s exospheres, by performing suitable hyper-velocity impact experiments onto representative ice-silicate targets. 

This is achieved by accelerating suitable micron and submicron-sized solar system analogue dust particles with the 2MV dust accelerator of the IRS at the MPA of the University of Stuttgart to speeds in excess of 100 km/s.

Such experiments have not been performed so far as they require a highly specialized experimental environment and equipment:  

The set up must provide the capability for the ice-silicate sample production of suitable dimensions (diameter and height) with compositions and structures matching those of the current best knowledge of those of Callisto, Ganymede and Europa and for the acceleration of suitable dust particles under very controlled conditions at the same location. 

In addition, the complete laboratory layout and experimental set up must allow the safe and controlled transfer of the produced sample into the experimental set up.  

Furthermore, the experimental set up has to provide suitable and reliable cooling for the ice-silicate targets for the whole duration of the measurements as well as the suitable environment for the detectors needed for the conduction of the planned measurements. 

The newly developed experimental set up at the dust accelerator laboratory in Stuttgart meets these requirements: 

 

The ice-dust samples are produced in a specific process ensuring smoothness of the target upper surface and homogenous distribution of the ice-dust mixture in an protected environment set up in a compact off-the-shelf glove box ("Glove-Bubble").

The safe transport to the vacuum chamber is achieved by covering the sample with a protective capsule mechanism to minimize contamination during transfer into a small vacuum vessel (airlock) located in front of the experimental chamber. 

After the airlock is evacuated and the pressures in the airlock and experimental chamber are matched, the capsule is removed, the gate between the airlock and the chamber opened. 

The sample is moved into its final position with the linear feedthrough supporting the sample mount as well as the cooling and electrical infrastructure. The vacuum chamber’s design (down to 10-7 mbar and -100°C) allows for simultaneous measurements of the ions and neutral elements generated upon impacts on the ice target as well as the emerging secondary particles (ejecta).