Mapping a duck: geological features and region definitions on comet 67P/Churyumov-Gerasimenko

Abstract

The data from the Rosetta mission have permitted a reconstruction of the shape of comet 67P/Churyumov-Gerasimenko and an identification of the terrains and features forming the surface. The peculiar shape of the comet has made it challenging to project these geological features onto an unambiguous frame. As a result, the geological maps published to date are created on top of comet images, making them dependent on the viewing angle and image resolution. To overcome this limitation, we present an integrated set of geological maps of the northern hemisphere of the comet, displayed in an unambiguous projection. The new maps combine the geological landmarks published in previous studies in a single framework and are completed with newly identified features. We have located the landmarks on OSIRIS images projected onto the surface of a three-dimensional shape model of the comet. For each region, the geological maps are displayed in the Quincuncial adaptive closed Kohonen (QuACK) map projection. The QuACK map solves the spatial ambiguity issues and reduces the shape and area distortions of classical global projections, which particularly affect the polar regions. The outcome of this research is a set of individual geological maps that are displayed both on top of OSIRIS images and in the QuACK map projection. These maps are analysed and grouped by similarities in terrain and morphology to find common characteristics that allow expanding our knowledge of the formation processes of comets. Based on this analysis, the north-south dichotomy is confirmed, and a redefinition of the regional boundaries is proposed for the Anubis-Atum and Aker-Babi frontiers. This research fills the gap in the field of mapping comet 67P/Churyumov-Gerasimenko and provides an innovative method for treating the surface of highly irregular bodies.