Cambianica, Pamela (2019) Morphological and compositional analysis of boulder distributions on comet 67P/Churyumov-Gerasimenko. [Ph.D. thesis]
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Abstract (italian or english)
The European Space Agency's Rosetta mission consisted of the orbiter spacecraft Rosetta and the lander Philae. Launched in 2004, the space probe reached the comet 67P/Churyumov-Gerasimenko after a journey lasted more than ten years. The objectives of the mission were to map the comet, to study its composition, to investigate the chemical and thermal properties, and to monitor the activity during its journey in the inner Solar System. Rosetta was the first mission to rendezvous with a comet, and to deploy a lander on a comet's surface. From a wider prospective, the Rosetta mission allowed to investigate the origin of comets, and to define the implication for the origin of the Solar System. We used OSIRIS Narrow Angle Camera with a spatial scale smaller than 2 m=pixel to analyze the surface of comet 67P. The surface reveals a variety of terrains and geological features, suggesting to be a very active and complex environment. In the first part of the thesis, a detailed quantitative analysis of isolated boulder fields is provided. We used different techniques to supply a method for analyzing the morphology of the boulders, which represent one of the ubiquitous and most important geological features on the comet. In the second part, a method to measure the seasonal evolution of Hapi's deposit is described, providing an upper limit for Hapi's water ice fraction. Measuring the evolution of the heights of some boulders, we fixed the pristine 67P ice content, and we compared the results with the Inter-Stellar Medium and CI-Chondrites. Finally, we investigated the macroscopic thermomechanical behavior of a 40 meter boulder located on the Imhotep region by modeling its response to diurnal thermal forcing. Preliminary results reveal that stresses occur in the boulder's exteriors due to the sudden variation in temperature during sunset and sunrise. We explored whether the simulated stress is enough to propagate preexisting cracks, discussing the implications for rock breakdown.
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