Space Weathering Effects on Iron‐Bearing Phyllosilicates, Iron Oxyhydroxide and Basalt Simulated by Nanosecond Pulse‐Laser Irradiation

Abstract The forthcoming MMX (Martian Moon eXploration) mission will carry the MIRS instrument (MMX Infrared Spectrometer) to study the composition of the Martian system. On airless bodies, like Phobos and Deimos, micrometeorite bombardment can strongly modify the spectral properties of their surface materials. To better identify the effects of micrometeorite bombardment on infrared spectroscopy data, we have simulated, using nanosecond pulse‐laser irradiation experiments, micrometeorite impacts on minerals and rock relevant for the surface composition of Phobos and Deimos based on our current knowledge. Laser irradiation was performed on pure mineral phases (i.e., nontronite, antigorite, biotite, goethite) and basalt, and their reflectance spectral properties were acquired between 0.5 and 3.6 μm. Our results reveal that laser impacts can reduce the strength of specific absorption bands characteristic of these minerals. In addition, laser impacts can also significantly modify the position of specific absorption bands, especially for phyllosilicates. Iron features originally near 0.65–0.75 μm, and the 2.8 μm O/OH bands are the most affected. They can shift up to a few tens of nanometers toward shorter or longer wavelengths, depending on the sample. The overlap between the iron band positions (e.g., between altered antigorite and pristine nontronite) suggests that space weathering can distort the accurate identification of minerals using infrared spectroscopy. Finally, we observed that the signature of antigorite subjected to micrometeorite bombardment is close to the signature observed on Phobos with CRISM data. Therefore, we believe that this mineral should be seriously considered as a potential constituent of the Phobos regolith.