Surface Properties and -Processes on Phobos from Spectrophotometric Data by HRSC (High Resolution Stereo Camera) on Mars Express

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We will characterize the spectrophotometric properties of Phobos to improve our understanding of the surface structure and the dynamic processes causing the distinct albedo and color patterns observed on this Martian satellite. We benefit from most recent narrow-band color and panchromatic data by HRSC (High-Resolution Stereo Camera) on Mars Express, obtained from a wide range of illumination phase angles and at high spatial resolution. The HRSC coverage includes Phobos’ trailing hemisphere and the farside, not observable by other currently Mars-orbiting spacecraft. Data from more than 327 Phobos flybys are available, and more data are expected to come. We determine disk-resolved photometric function(s), which will be used to map photometric properties of Phobos’ surface and to identify local albedo anomalies, representing e.g., areas of increased surface roughness. Furthermore, we use data from HRSC color channels to map multispectral properties of Phobos’ surface at the camera’s high spatial resolution. Results of our mapping will be compared with instrument data from previous missions, where Phobos’ well-known „red“ and „blue“ spectral units have been identified. The characteristics of Phobos’ regolith and the multispectral units will be discussed in terms of surface structure and dynamic processes, such as emplacement of crater ejecta and space weathering. Our proposed project is timely in the light of MMX (Martian Moon Explorer), JAXA’s sample return mission to Phobos, which is currently being prepared. We will make recommendations for choices of landing sites and sampling strategy to maximize the science return of this upcoming mission. The team from Technical University Berlin and the DLR Institute of Planetary Research is uniquely experienced to carry out this proposed study.