Preliminary results of experimental investigations of the transfer of Martian material to Phobos

The transfer of material between the surfaces of Mars and Phobos is thought to be a key parameter in understanding the formation/evolution of the Martian moons. Past numerical investigations have predicted that, on average, 255 ppm of Martian material should be detectible within the Phobosian regolith. Due to impact gardening processes, this material is assumed to be evenly distributed throughout the regolith material. It is hoped that upon arrival at Phobos, the MMX spacecraft will be capable of identifying the distributed Martian material on Phobos. The main assumption behind the numerical studies is that the Martian material is distinguishable from the Phobosian regolith. The work presented here provides an initial experimental investigation of this assumption, investigating the transport of material from Mars to its moons.

We will use the Kent single-stage light-gas gun to simulate the effect of ejecta production on the Martian surface. We plan a programme of five shots over the speed range of 300-1000 m/s, covering the lower end of the speed regime thought to be relevant for impacts onto Phobos. Projectiles will be fired from a 0.22” (5.56 mm) smoothbore barrel and consisted of a 5.56 mm diameter by 6 mm long 3D-printed UV cured resin shell. The shell is filled with a granular mixture of MGS-1 (Martian simulant) and europium acetate hydrate (Eu(CH3CO2)3·XH2O) as an elemental tracer. The resin shell allows the granular material to be contained, ensuring it impacts the target as a single projectile rather than a dispersed powder. This bespoke projectile construction method provides a complex geological impactor with an elemental tracer to aid in post-shot analysis. Targets will consist of ‘cemented’ PCA-1 Phobos simulant bricks, formed from a mixture of PCA-1 simulant, de-ionised water, and methanol (in the ratio of 60:10:30 wt.%). The mixture is baked in a silicone mould for a period of 24 hours at 80°. During this time the water combined with the clay materials in the simulant causing them to set. During baking, the methanol component evaporates away leaving evenly distributed pore spaces.

Following each shot, analyses is performed on both the impact crater and the collected ejecta. The ejecta material is analysed via x-ray fluorescence and diffraction, focusing on the detection and distribution of potential projectile material. The chemical compositions of the MGS-1 and PCA-1 simulants are highly similar (with NaO being the only component unique to the MGS-1 simulant). The inclusion of the Eu elemental tracer is critical in providing a simple method to confirm the presence projectile material. Analysis of the crater will investigate the distribution of the emplaced projectile material within the target. SEM-EDS analysis of slices through the craters provides a method to investigate both the relative position and depth of any emplaced projectile material. I will report on the bespoke projectile construction and the method of target production. Initial result from the performed shots will also be presented.