Regional Surface Morphology of Comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images

Abstract

Aims. The OSIRIS camera onboard the Rosetta spacecraft has been acquiring images of the comet 67P/ Churyumov-Gerasimenko (67P/ C-G)’s nucleus at spatial resolutions down to ~ 0.17 m/px since Aug 2014. These images have yielded unprecedented insight into the morphological diversity of the comet’s surface. This paper presents an overview of the regional morphology of comet 67P/ C-G. Methods. We use the images that were acquired at orbits ~ 20–30 km from the center of the comet to distinguish different regions on the surface and introduce the basic regional nomenclature adopted by all papers in this issue that address the comet’s morphology and surface processes. We use anaglyphs to detect subtle regional and topographical boundaries, and images from close orbit (~ 10 km from the comet’s center) to investigate the fine texture of the surface. Results. Nineteen regions have currently been defined on the nucleus based on morphological and / or structural boundaries and can be grouped into distinctive region types. Consolidated/fractured regions are the most common region type. Some of these regions enclose smooth units that appear to settle in gravitational sinks or topographically low areas. Both comet lobes have a significant portion of their surface covered by a dusty coating that appears to be recently emplaced and shows signs of mobilization by aeolian-like processes. The dusty coatings overlie most of the regions on the surface but are notably absent from a couple of irregular large depressions that show sharp contacts with their surroundings and talus-like deposits in their interiors, which suggests that short-term explosive activity may play a significant role in shaping the comet’s surface in addition to long-term sublimation loss. Finally, the presence of layered brittle units showing signs of mechanical failure predominantly in one of the comet’s lobes can indicate a compositional heterogeneity between the two lobes.