Compositional Variations of Titan\u27s Impact Craters Indicates Active Surface Erosion

Impact craters on Titan are relatively scarce, but provide ample information about the subsurface properties and modification processes present there. This study utilizes impact craters to examine compositional variations across Titan’s surface and their subsequent modification. Fifteen craters and their ejecta blankets were studied. Subsurface composition was inferred from emissivity data from Cassini’s RADAR instrument, and surficial composition from Cassini’s Visible and Infrared Mapping Spectrometer (VIMS). Results show subsurface composition of these craters is controlled by their degradation state and local environment. Older craters are more infilled with organics than younger, and dunes craters show more organic enrichment than plains craters. Surficial composition is only controlled by the local environment (i.e. dunes or plains regions). Since degraded craters show organic rich subsurfaces, but varying surface compositions, it is likely there is an active surface process clearing the surface of sediments and infilling the craters’ subsurface fractures

Aqueous alteration processes in Jezero crater, Mars—implications for organic geochemistry

The Perseverance rover landed in Jezero crater, Mars, in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep-ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, which probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks and are preserved in minerals related to both aqueous environments

Compositional Variations of Titan's Impact Craters Indicates Active Surface Erosion

International audienceTitan’s crust is assumed to be mostly water-ice. However, the surface composition is not well constrained due to its thick atmosphere. Based on infrared and radiometry data, the surface appears enriched in organics, with only few areas showing evidence of exposed water-ice. Regions of water-ice enrichment include the rims and ejecta blankets of impact craters. This study utilizes these geologic features to examine compositional variations across Titan’s surface, and their subsequent modification due to erosional processes.Sixteen craters and their ejecta blankets were mapped on a Cassini RADAR mosaic. These features were selected because they are some of the best preserved craters on Titan. Composition was inferred from Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) and 2-cm emissivity data from the Cassini radiometer. With VIMS, different compositional units were inferred from their reflectivity at specific wavelengths. With the emissivity data, high values suggest more organic-rich material, while lower values indicate strong volume scattering. Areas with low emissivity have been interpreted to be water-ice rich, as water-ice is a favorable medium for volume scattering.Results show fresher, well-preserved craters in the dunes regions have a low emissivity indicative of water-ice, and a VIMS spectrum consistent with an unknown material, possibly a mixture of water-ice and organics. As these craters erode over time, the VIMS spectra remain the same but the emissivity increases. Well-preserved craters in the mid-latitude plains show VIMS spectra and emissivity values consistent with water-ice. As these plain craters degrade, the VIMS spectra remain the same, but the emissivity increases. The differing VIMS signatures suggest more mixing with organics during the cratering event in the organic-rich dunes than the plains. The changes in emissivity over time are consistent with organic infilling of subsurface fractures in both regions, with limited surficial alteration. These results support the idea that compositional variations in Titan’s impact craters are related primarily to erosion and infilling, and to a lesser extent, local variations in the overlying organic material of the pre-impact substrate

Selection and Characteristics of the Dragonfly Landing Site near Selk Crater, Titan

International audienceThe factors contributing to the initial selection of a dune site near the Selk impact structure on Titan as the first landing site for the Dragonfly mission are described. These include arrival geometry and aerodynamic/ aerothermodynamic considerations, illumination, and Earth visibility, as well as the likely presence of exposed deposits of water-rich material, potentially including materials where molten ice has interacted with organics. Cassini observations of Selk are summarized and interpreted: near-infrared reflectance and microwave emission data indicate water-rich materials in and around the crater. Radar topography data shows the rim of Selk to have slopes on multi-km scales reaching only ∼2°degrees, an order of magnitude shallower than early photoclinometric estimates