[1] On the basis of High Resolution Imaging Science Experiment (HiRISE) images of two successive years we observed changes of a gully on the Russell crater dune field. Within the first year the length of a ∼2 m wide incised gully channel grew about 50 m downslope, and ∼120 m within in the second year. Gully activity occurred in early spring between L S ∼198°and ∼218°in the first year and between L S ∼192°and ∼221°in the second year. Based on the channel morphology, spectral data and modeled surface temperatures, the changes can be best explained with transient melting of small amounts of H 2 O-ice triggering slurry flows consisting of sand mixed with liquid water. Citation: Reiss, D., G. Erkeling, K. E.Bauch, and H. Hiesinger (2010), Evidence for present day gully activity on the Russell crater dune field, Mars, Geophys. Res. Lett., 37, L06203,

[1] On Earth, the thawing of permafrost deposits with high-ground ice content results in massive surface subsidence and the formation of characteristic large thermokarst depressions. Slope asymmetries within thermokarst depressions suggest lateral growth, which occurs due to thermoerosion and gravimetric mass wasting along these slopes. It has been proposed that rimless, asymmetrically shaped depressions (called scalloped depressions) on Mars were formed by insolation-driven ground ice sublimation. We investigated a large thermokarst depression in ice complex deposits in the Siberian Arctic as a terrestrial analogue for scalloped depressions in Martian volatile-rich mantle deposits. Our results from field studies, insolation modeling, and geomorphometric analyses suggest lateral thermokarst development in a northern direction. This conclusion is obvious due to steeper slope angles of the south facing slopes. Insolation and surface temperatures are crucial factors directly influencing thermokarst slope stability and steepness. Comparative analyses of Martian scalloped depressions in Utopia Planitia were conducted using high-resolution (High-Resolution Imaging Science Experiment, Context Camera) and thermal infrared (Thermal Emission Imaging System) satellite data. By direct analogy, we propose that the lateral scalloped depression development on Mars was primarily forced on the steep pole-facing slopes in the equator-ward direction. Insolation modeling confirms that this must have happened in the last 10 Ma during an orbital configuration of higher obliquity than today. Development would have been maximized if the orbit was both highly oblique and highly eccentric, and/or the Martian summer coincided with perihelion. Relatively short events of increasing sublimation or even thawing of ground ice led to fast slumping processes on the steep pole-facing slopes.

Launched onboard the BepiColombo Mercury Planetary Orbiter (MPO) in October 2018, the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is on its way to planet Mercury. MERTIS consists of a push-broom IR-spectrometer (TIS) and a radiometer (TIR), which operate in the wavelength regions of 7-14 μm and 7-40 μm, respectively. This wavelength region is characterized by several diagnostic spectral signatures: the Christiansen feature (CF), Reststrahlen bands (RB), and the Transparency feature (TF), which will allow us to identify and map rock-forming silicates, sulfides as well as other minerals. Thus, the instrument is particularly well-suited to study the mineralogy and composition of the hermean surface at a spatial resolution of about 500 m globally and better than 500 m for approximately 5-10% of the surface. The instrument is fully functional onboard the BepiColombo spacecraft and exceeds all requirements (e.g., mass, power, performance). To prepare for the science phase at Mercury, the team developed an innovative operations plan to maximize the scientific output while at the same time saving spacecraft resources (e.g., data downlink). The upcoming fly-bys will be excellent opportunities to further test and adapt our software and operational procedures. In summary, the team is undertaking action at multiple levels, including performing a comprehensive suite of spectroscopic measurements in our laboratories on relevant analog materials, performing extensive spectral modeling, examining space weathering effects, and modeling the thermal behavior of the hermean surface.

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