Sputter yields of rough surfaces: Importance of the mean surface inclination angle from nano- to microscopic rough regimes

Creation of Lunar and Hermean analogue mineral powder samples for solar wind irradiation experiments and mid-infrared spectra analysis

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. 

Deducing Lunar Regolith Porosity From Energetic Neutral Atom Emission

Abstract Solar wind (SW) ion irradiation on airless bodies can play an important role in altering their surface properties and surrounding exosphere. Much of the ion sputtering data needed for exosphere studies come from binary collision approximation sputtering models such as TRansport of Ions in Matter and its more recent extension, SDTrimSP. These models predict the yield and energy distribution of sputtered atoms, along with the depth of deposition and damage of the substrate, all as a function of the incoming ion type, impact energy, and impact angle. Within SDTrimSP there are several user-specific inputs that have been applied differently in previous SW ion sputtering simulations. These parameters can influence the simulated behavior of both the target and sputtered atoms. Here, we have conducted a sensitivity study into the SDTrimSP parameters in order to determine a best practice for simulating SW ion impacts onto planetary surfaces. We demonstrate that ion sputtering behavior is highly sensitive to several important input parameters including the ion impact angle and energy distribution and the ejected atom surface binding energy. Furthermore, different parameters can still result in similarities in the total sputtering yield, potentially masking large differences in other sputtering-induced behaviors such as the elemental yield, surface concentration, and damage production. Therefore, it is important to consider more than just the overall sputtering behavior when quantifying the importance of different parameters. This study serves to establish a more consistent methodology for simulations of SW-induced ion sputtering on bodies such as Mercury and the Moon, allowing for more accurate comparisons between studies. 

Establishing a Best Practice for SDTrimSP Simulations of Solar Wind Ion Sputtering

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 O2+ 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+, O2+, C+, and CO2+ 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 O2+ and CO2+ in the low keV range shows no deviations in the sputtering yields attributable to molecular effects. Therefore, CO2+ 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.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020JE006583

Experimental Insights Into Space Weathering of Phobos: Laboratory Investigation of Sputtering by Atomic and Molecular Planetary Ions

The surface of Mercury is continuously exposed to impinging solar wind ions To improve the understanding of space weathering and exosphere formation, a detailed investigation of the ion-surface interaction is necessary Magnesium and iron rich pyroxene (Ca,Mg,Fe)2[Si2O6] samples were used as analogues for Mercury’s surface and irradiated with He+ ions at solar wind energies of 4 keV Several regimes of implantation and sputtering were observed there The total estimated mass of implanted He coincides with the mass decrease due to He outgassing during subsequent Thermal Desorption Spectroscopy measurements Comparison to established modeling efforts and SDTrimSP simulations show that a He saturation concentration of 10 at% has to be assumed A complete removal of He is observed by heating to 530 K On the surface of Mercury, temperatures between about 100 K and 700 K are expected This temperature will therefore influence the implantation and release of He into Mercury’s exosphere

/pdf/solar-wind-helium-ion-interaction-with-mg-and-fe-rich-49p0kf8a6f.pdf

Solar wind Helium ion interaction with Mg and Fe rich pyroxene as Mercury surface analogue

A detailed look on the interaction of solar wind helium with Mercury's surface in the laboratory

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Solar wind Helium ion interaction with Mg and Fe rich pyroxene as Mercury surface analogue

A detailed look on the interaction of solar wind helium with Mercury's surface in the laboratory