Mapping a Duck: Geological Features and Region Definitions on Comet 67P/Churyumov-Gerasimenko

<p>The data from the Rosetta mission enabled the reconstruction of the shape of comet 67P/Churyumov-Gerasimenko (hereafter 67P) and the identification of the terrains and features forming its surface. The highly irregular  shape of the comet poses a challenge for the depiction of these geological features on two-dimensional maps. Standard global map projections cannot display the complete surface of 67P because different points on the surface can have the same longitude and latitude.  As a consequence, the geological maps published to date are  created on top of comet images, making them dependent on the viewing angle and image coverage and resolution.</p><p>Here, we make use of the recently published Quincuncial Adaptive Closed Kohonen (QuACK) map. It projects the complete surface of 67P unambiguously onto a square. The QuACK map is topologically equivalent to the Peirce quincuncial projection of the world, which makes it  possible to define generalized longitudes and latitudes. These can be used within any global map projection in order to obtain an  unambiguous QuACK version.</p><p>The mapping of geological features is carried out in three dimensions employing the Small Body Mapping Tool (SBMT). We use images from  the OSIRIS Narrow Angle Camera aboard Rosetta which have been projected onto the shape model of the SBMT. The three-dimensional coordinates are then projected onto two-dimensional maps, either in the QuACK map projection or in the QuACK version of  the equidistant cylindrical projection. We present individual maps for 17 of the 26 regions of 67P, mostly located in the northern  hemisphere. The new maps combine features published in previous studies with newly identified features.</p><p>We discuss the distribution of geological features and the characteristics of the regions. In order to align region boundaries with geological features, we propose two modifications of region definitions.</p>

Quincuncial adaptive closed Kohonen (QuACK) map for the irregularly shaped comet 67P/Churyumov-Gerasimenko

Context. Standard global map projections cannot display the complete surface of a highly irregular body such as the Rosetta target comet 67P/Churyumov-Gerasimenko because different points on the surface can have the same longitude and latitude. Aims. We present a concept of generalized longitudes and latitudes that allows us to display the complete comet in generalized versions of any standard map projection. Methods. A self-organizing Kohonen map can be used to sample the surface of any 3D shape, but the unfolded map misses some area beyond its edges. Here, we combine two square grids into an inherently closed structure that really maps the complete surface of the comet. Beyond this, the closed map is topologically equivalent to the Peirce quincuncial projection of the world, which enables the definition of generalized longitudes and latitudes. Results. While the generalized version of any map projection does not exactly share the properties of the original, such as preservation of area or shape, it behaves very similar. In particular, the generalized version of the quincuncial projection behaves very well over most of the surface area and shares the tessellation properties with its original. Conclusions. The quincuncial adaptive closed Kohonen (QuACK) map and the concept of generalized longitudes and latitudes provide means for global maps of arbitrarily irregular shapes.

Preparation of reduced graphene oxide coated flaky carbonyl iron composites and their excellent microwave absorption properties

A absorber with frequency dispersion behavior was prepared by complete surface coating of reduced graphene oxide on flaky carbonyl iron.