Abstract Investigating the space weathering of the Martian moon Phobos represents an important step toward understanding the development from its origin to its present‐day appearance. Depending on Phobos’ orbital position, its surface is continuously sputtered by the solar wind and planetary ions that originate in the Martian atmosphere. Based on Mars Atmosphere and Volatile Evolution measurements, it has been proposed that sputtering by planetary O + and O 2 + ions dominates in the Martian tail region, where the planet mostly shadows Phobos from the solar wind. In these models, uncertainties for sputtering yield inputs still exist due to the lack of sufficient analog experiments. Therefore, sputtering measurements with O + , O 2 + , C + , and CO 2 + ions between 1 and 5 keV were performed using augite samples as Phobos analogs. The experimental results for O + irradiations show smaller mass changes than predicted by SDTrimSP simulations, which probably can be attributed to O implantation enabled by the Fe content of the target. Sputtering with O 2 + and CO 2 + in the low keV range shows no deviations in the sputtering yields attributable to molecular effects. Therefore, CO 2 + ions will most likely be negligible for the sputtering of Phobos according to the current understanding of ion fluxes on the Martian moon. Ultimately, our experiments suggest that the sputtering contribution on Phobos by O ions is about 50% smaller than previously assumed. This does not change the qualitative outcome from previous modeling stating that planetary O ions are by far the dominant sputtering contribution on Phobos in the Martian tail region.
The surfaces of airless planetary bodies are subject to a barrage of charged particles, photons, and meteoroids. This high-energy space environment alters the surfaces and creates a tenuous atmosphere of ejected particles surrounding the celestial bodies. Experiments with well characterized analogue materials under controlled laboratory conditions are needed to interpret the observations of these atmospheres and improve composition models of such bodies. This study presents methods to create and analyze mineral powder pellets for ion irradiation experiments relevant for rocky planetary bodies including the Moon and Mercury. These include the pyroxenes diopside and enstatite, the plagioclase labradorite and the non-analogue pyroxenoid wollastonite. First ion irradiation experiments with diopside, enstatite and wollastonite pellets were performed under UHV with 4 keV He+ at fluences of several 1021 ions m−2 (~100 and ~1000 years for Mercury and the Moon, respectively). The pellet's thermal IR reflectance properties were compared before and after irradiation showing monotonously shifting IR spectral features between 7 − 14 μm towards higher wavelengths. For all irradiated pellets, Reststrahlen bands shifted by ~0.03 μm. Surface abrasion was found to remove the sputter effect, which is restricted to the top few tens of nm of the surface. Additionally, ion irradiation experiments were performed in a quartz crystal microbalance catcher setup, where the mass sputtered from pellets was monitored. This proves, that the presented sample preparation method allows the study of irradiation induced sputtering and surface alteration on the surfaces of rocky planets under laboratory conditions.
A quartz crystal microbalance was used to experimentally study the erosion of tungsten during rapidly alternating bombardment with 2 keV argon and deuterium projectiles. A key goal was to investigate whether the mean sputtering yield of the alternating irradiation can be predicted from data for sputtering yields of single ion species. In addition, influences by residual gas pressure in the UHV experiment and variable ion fluxes have been studied. Our results show that the mean sputtering yield of irradiations with alternating ion species can be well predicted for a range of different fluence ratios as a simple superposition of individual sputtering yields, weighted by the respective relative fluences. This finding supports that no synergistic sputtering effects were relevant in the investigated low-flux regime.
Abstract The porosity of the upper layers of regolith is key to the interaction of an airless planetary body with precipitating radiation, but it remains difficult to characterize. One of the effects that is governed by regolith properties is Energetic Neutral Atom (ENA) emission in the form of reflected and neutralized solar wind protons. We simulate this process for the surface of the Moon by implementing a regolith grain stacking in the ion‐solid‐interaction software SDTrimSP‐3D, finding that proton reflection significantly depends on the regolith porosity. Via comparison with ENA measurements by Chandrayaan‐1, we derive a globally averaged porosity of the uppermost regolith layers of . These results indicate a highly porous, fairy‐castle‐like nature of the upper lunar regolith, as well as its importance for the interaction with impacting ions. Our simulations further outline the possibility of future regolith studies with ENA measurements, for example, by the BepiColombo mission to Mercury.
This study investigates the sputtering properties of nano-columnar tungsten surfaces under 2 keV D2+ irradiation. It was conducted both by performing experiments in a highly sensitive quartz crystal microbalance setup as well as by numerical methods using two simulation codes called SPRAY and SDTrimSP-3D. A key question was whether the strong sputtering yield reduction observed in previous studies under 2 keV Ar+ irradiation is maintained when using a much lighter ion species like deuterium. For the latter, a substantially larger projected range in the material has to be expected. Therefore, a total confinement of the ion-solid interaction within the W nano-columns cannot be assumed a priori. However, both the experiments and the numerical simulations showed in good agreement that the geometrically induced sputtering yield reduction is still observed to the same extent despite the increased range of ions in the material. Thus, a potential application of such nano-columnar tungsten surfaces as plasma facing components in future nuclear fusion devices is not affected.
