Reconstructing the layerings on comet 67P/Churyumov-Gerasimenko

Funding institution: Max Planck Institute for Solar System Research, Göttingen

In collaboration with: Dr. Hermann Böhnhardt, Prof. Dr. Andreas Pack, Prof. Dr. Ulrich Christensen, Dr. Matthias Schröter, Dr. Luca Penasa (University of Padua, Italy), Emile Remetean (CNES, France), Benoît Dolives (Magellium, France)

Research framework: PhD thesis at the University of Göttingen (2016-2020)

During the past decades, spacecraft missions to cometary nuclei revealed that their surfaces are complex and diverse. Most recently, the ’Rosetta’ mission to comet 67P/Churyumov-Gerasimenko (’comet 67P’) delivered spectacular images of its nucleus at unprecedented resolution, showing smooth plains, flat terraces, steep cliffs, circular pits, and indications of global layerings. In the years since Rosetta arrived at the comet, it has been a matter of intense study how and when those apparent layerings were formed in the cometary nucleus. By merging techniques of structural geology, statistical image processing, and solar system science, I aimed to contribute to the understanding of the formation of the layerings, and consequently the formation of the nuclei as a whole.

I used two distinctive approaches to study the layerings’ orientation on both lobes of comet 67P’s nucleus. In the first approach, I mapped layering-related linear features on the nucleus surface, meaning the edge-lines of morphological terraces as well as the traces of internal strata where they intersect with the surface along hill slopes. I mapped these lineaments on a three-dimensional shape model of the nucleus, onto which I projected high-resolution images for clearer spatial orientation. This method locally improved the spatial resolution by more than an order of magnitude. By mapping only lineaments of substantial curvature, I was then able to fit planes through the nodes that make up the lineaments. I compared those planes’ normal vectors to normals determined by other authors in similar or identical locations, albeit using different methods. In this way, I confirmed their 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. (Ruzicka et al., 2018)

In the second approach, I developed a Fourier-based image analysis algorithm to detect lineament structures at pixel-precision. I used this algorithm to analyse the Hathor cliff on the Small Lobe of comet 67P, where layering-related, sub-parallel linear features are freshly exposed. I found it 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, the algorithm has a higher signal-to-noise detection sensitivity than a human researcher and also reduces over-interpretation due to human biases. (Ruzicka et al., 2021)


Comet 67P/C.-G. as seen by Rosetta on 22 Aug. 2014. Image width ca. 7 km (ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0)
Mapping coordinate-points (blue dots) along layering-related linear features on a 3D rendering of the comet's surface (first approach). (© Birko Ruzicka, do not copy without permission)
The Hathor cliff on comet 67P, area studied in the second approach is marked in red. (© Birko Ruzicka, do not copy without permission)

Mapping Earth’s depositional hiatuses

Funding institution: Ludwig-Maximilians-Universität München

In collaboration with: Prof. Dr. Anke Friedrich, Prof. Dr. Hans Peter Bunge, Roland Neofitu, Vladimir Shipilin

Research framework: Interdisciplinary research project at the departments for Geology and Geophysics (2015-2016)

In this ongoing project, we are mapping and interpolating the surfaces of ‘missing time’ on geological maps of several spatial scales. The project is described in detail in Friedrich et al. (2018).


Hiatus duration below deposits of Miocene age on the geological map of Europe (© Birko Ruzicka, do not copy without permission)

Terrestrial impact craters as markers for erosion

Funding institution: Ludwig-Maximilians-Universität München

In collaboration with: Prof. Dr. Anke Friedrich

Research framework: Masters thesis (2015)

Erosion rates are difficult to quantify over long timescales with current methods, but meteorite impact craters can be used to constrain them.

The morphology of fresh impact craters is well understood. If a crater’s current morphology differs from the initial state, we can use this to quantify the modification that happened to the crater, and therefore to the crustal region it is embedded in. I compiled an extensive database of quantitative and qualitative parameters of impact structures on Earth, and analyzed the terrestrial impact inventory with regard to spatial distribution, age, and shape of the structures. In contrast to the almost entirely circular population of craters on other planets, more than a third of the impact structures on Earth are not circular, which suggests that they could be used as markers for tectonic strain. However, I discovered that erosion introduces too much uncertainty into crater morphology to reasonably quantify tectonic deformation via remote sensing. On the case of the Sudbury structure I demonstrated that an elliptical crater’s strain cannot simply be derived from its surface expression.

However, as most exposed impact structures are eroded to some degree, they can be used to constrain average erosion rates at their location. Based on the expected geometry of fresh impact craters, I derived a formula to approximate the eroded volumes at sufficiently preserved “simple” craters. Finally, I constrained minimum and maximum erosion rates for eroded craters based on the fact that at least the initial rim height has been eroded, but the structures are still visible so no more than a certain amount can be missing. Particularly this last method yielded intriguing results, giving maximum average erosion rates of less than 10 m/Ma for 15 impact structures excavated into the Superior Craton, the Baltic Shield, and the North Australian Craton.


(Cropped figure) Circles signify the known impact structures, fill-color corresponds to the average erosion rate at the structure. The basemap shows the tectonic ages of the continental crust, darker = older. (© Birko Ruzicka, do not copy without permission)
As Earth is a tectonically active planet, the fraction of non-circular impact structures within its impact inventory increases with time. (© Birko Ruzicka, do not copy without permission)

Dating of an alluvial fan (i.e. indirect dating of an earthquake)

Funding institution: Ludwig-Maximilians-Universität München

In collaboration with: Prof. Dr. Anke Friedrich, Prof. Dr. em. Fred M. Phillips, Dr. Shasta Marrero

Research framework: Bachelor thesis (2013)

Alluvial fans in tectonically active regions, such as the Basin and Range Province, USA, are good recorders of paleo-earthquakes and past climate conditions. We determined the age of an alluvial fan in the Schell Creek Range through 36Cl cosmogenic nuclide dating. The concentration of 36Cl in the samples indicates an approximate age of 129 ka. The method entails a rather large uncertainty, as a number of factors influence the concentration of 36Cl in the material and thus the calculated age. Those factors are: Geomagnetic field strength, erosion, shielding, weathering, geometry change, elevation changes, inheritance and the density of the material all influence the calculated age.

In my thesis, I discuss each of these factors’ significance on the resulting age in a sensitivity analysis. For this, I varied different input factors and assessed the effect on the results. The exposure age was determined using the older program CHLOE as well as the new CRONUScalc Matlab code. As expected, the results from CRONUScalc were much more accurate and dependable. The analysis returned that the system is not very sensitive to the water content or the bulk density of the samples.  We gained a closer understanding of the factors determining the accuracy of cosmogenic nuclide dating of alluvial fans, as well as the remaining limitations of the method.


Location of the sampling site in the Basin and Range Province, USA. (© Birko Ruzicka, do not copy without permission)
Sensitivity analysis: Effect of varying the parameters of density and erosion rate. (© Birko Ruzicka, do not copy without permission)