From a report submitted by Swarna Prava Das, National Institute of Science Education and Research, India
The scientific objective of this project was to understand the role of space weathering on Mercury by experimentally simulating dust impacts using a pulsed laser beam and solar-wind irradiation through ion implantation at energies comparable to those of solar-wind ions. Additionally, the study also aimed to understand the effect of temperature on the optical characteristics of laser- and ion-irradiated samples at 450 °C equatorial daytime surface conditions on Mercury. There is a lack of studies on the spectral properties of ion- and laser-irradiated samples at high temperatures relevant to the surface of Mercury.
The work was carried out at the German Aerospace Centre (DLR) in Berlin and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany, where low-iron (~1.5 wt% FeO) bearing pyroxene powders pressed to pellets were prepared as analogue materials for Mercury, followed by acquisition of their bidirectional reflectance spectra in the visible and near-infrared (VNIR) and mid-infrared (MIR) spectral regions and emissivity spectra at 100 °C, 200 °C, 300 °C, and 450 °C. Nanosecond pulsed laser beams were scanned on the pellets with a single laser pulse per spot and five consecutive pulses per spot with an energy of 15 mJ/pulse. Furthermore, another pellet of Diopside was exposed to 4 keV He⁺ ions up to a fluence of 1 × 10¹⁷ ions/cm². During the study, we also irradiated pellets from three CM chondrites (Jbilet Winselwan, Aguas Zarcas, and Mukundpura) with the same pulsed laser beam to understand the effect of micrometeorite impact on organic-rich surfaces. VNIR, MIR, and emissivity spectra show significant changes in the spectral slope, band contrast, and position both before and after laser and ion irradiation. The structural and chemical changes within the samples are being studied using transmission electron microscopy. The results from the study clearly show that the high temperatures in the equatorial region of Mercury play a significant role in affecting the products of space weathering and their optical properties, even if the surface has low iron content. These
results will be valuable for the interpretation of data being obtained by the BepiColombo mission to Mercury.