Wozniakiewicz, P. et al. (2015). The survivability of phyllosilicates and carbonates impacting Stardust Al foils: Facilitating the search for cometary water. Meteoritics & Planetary Science[Online]50:2003-2023. Available at: http://doi.org/10.1111/maps.12568.
The SMART-1 end-of-life impact with the lunar surface was simulated with impacts in a two stage light-gas gun onto inclined basalt targets with a shallow surface layer of sand. This simulated the probable impact site, where a loose regolith will have overlaid a well consolidated basaltic layer of rock. The impact angles used were at 5° and 10° from the horizontal. The impact speed was ~2 km s−1 and the projectiles were 2.03 mm diameter aluminum spheres. The sand depth was between approximately 0.8 and 1.8 times the projectile diameter, implying a loose lunar surface regolith of similar dimensions to the SMART-1 spacecraft. A crater in the basement rock itself was only observed in the impact at 10° incidence, and where the depth of loose surface material was less than the projectile diameter, in which case the basement rock also contained a small pit-like crater. In all cases, the projectile ricocheted away from the impact site at a shallow angle. This implies that at the SMART-1 impact site the crater will have a complicated structure, with exposed basement rock and some excavated rock displaced nearby, and the main spacecraft body itself will not be present at the main crater.
Price, M. et al. (2014). Limits on methane release and generation via hypervelocity impact of Martian analogue materials. International Journal of Astrobiology[Online]13:132-140. Available at: http://dx.doi.org/10.1017/S1473550413000384.
The quantity of methane in Mars' atmosphere, and the potential mechanism(s) responsible for its production, are still unknown. In order to test viable, abiotic, methangenic processes, we experimentally investigated two possible impact mechanisms for generating methane. In the first suite of experiments, basaltic rocks were impacted at 5 km s−1 and the quantity of gases (CH4, H2, He, N2, O2, Ar and CO2) released by the impacts was measured. In the second suite of experiments, a mixture of water ice, CO2 ice and anhydrous olivine grains was impacted to see if the shock induced rapid serpentinization of the olivine, and thus production of methane. The results of both suites of experiments demonstrate that impacts (at scales achievable in the laboratory) do not give rise to detectably enhanced quantities of methane release above background levels. Supporting hydrocode modelling was also performed to gain insight into the pressures and temperatures occurring during the impact events.
Wozniakiewicz, P. et al. (2014). Micron-scale hypervelocity impact craters: Dependence of crater ellipticity and rim morphology on impact trajectory, projectile size, velocity, and shape. Meteoritics & Planetary Science[Online]49:1929-1947. Available at: http://doi.org/10.1111/maps.12364.
The interstellar collector on NASA's Stardust mission captured many particles from sources other than the interstellar dust stream. Impact trajectory may provide a means of discriminating between these different sources, and thus identifying/eliminating candidate interstellar particles. The collector's aerogel preserved a clear record of particle impact trajectory from the inclination and direction of the resultant tracks. However, the collector also contained aluminum foils and, although impact crater studies to date suggest only the most inclined impacts (>45° from normal) produce crater morphologies that indicate trajectory (i.e., distinctly elliptical), these studies have been restricted to much larger (mm and above) scales than are relevant for Stardust (μm). It is unknown how oblique impact crater morphology varies as a function of length scale, and therefore how well Stardust craters preserve details of impactor trajectory. Here, we present data from a series of impact experiments, together with complementary hydrocode modeling, that examine how crater morphology changes with impact angles for different-sized projectiles. We find that, for our smallest spherical projectiles (2 μm diameter), the ellipticity and rim morphology provide evidence of their inclined trajectory from as little as 15° from normal incidence. This is most likely a result of strain rate hardening in the target metal. Further experiments and models find that variation in velocity and impactor shape complicate these trends, but that rim morphology remains useful in determining impact direction (where the angle of impact is >20° from normal) and may help identify candidate interstellar particle craters on the Stardust collector.
Foster, N. et al. (2013). Identification by Raman spectroscopy of Mg–Fe content of olivine samples after impact at 6kms−1 onto aluminium foil and aerogel: In the laboratory and in Wild-2 cometary samples. Geochimica Et Cosmochimica Acta[Online]121:1-14. Available at: http://dx.doi.org/10.1016/j.gca.2013.07.022.