Layerings in the nucleus of comet 67P/Churyumov-Gerasimenko

Birko-Katarina Ruzicka
Dissertation, Georg-August-Universität Göttingen, 2019

The Rosetta mission to delivered images of comet 67P’s nucleus at unprecedented resolution which indicate the presence of a global layering system. By merging techniques of structural geology, statistical image processing, and solar system science, this thesis aims to contribute to the understanding of the formation of the layerings, and consequently the formation of cometary nuclei as a whole. I describe the two distinctive approaches I used to study the layerings’ orientation on both lobes of comet 67P’s nucleus. First, I mapped layering-related linear features on a 3D shape model of the nucleus, onto which I projected high-res OSIRIS images. I selected only lineaments of substantial curvature, and used a plane-fitting algorithm to find the normals to the layering planes represented by these lineaments. I used the normals to confirm previous authors’ results, including that the layering systems on the comet’s two lobes are geometrically independent from each other. My results rule out the proposal that 67P’s lobes represent collisional fragments of a much larger, layered body. Second, I developed a Fourier-based image analysis algorithm to detect lineament structures at pixel-precision. I analysed the layering-related, sub-parallel linear features exposed on the Hathor cliff on the comet’s Small Lobe. I found my algorithm to be a broadly applicable, powerful tool for automating the detection of layerings in images where conventional edge-detection algorithms are not effective. When correctly configured to the target conditions, I found the algorithm to have a higher signal-to-noise detection sensitivity than a human, while also reducing over-interpretation due to bias. In summary, I studied the layerings in the nucleus of comet 67P using several unconventional approaches and constrained their lateral extent, curvature, and to a degree also their thickness. Ultimately, I nominated two mechanisms that could have formed these layerings in cometary nuclei.