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Giroud-Proeschel, Elisabeth

University of British Columbia

Hollows are steep-walled, shallow, rimless depressions on the surface of Mercury. Commonly associated with bright deposits possibly related to volatile loss, these features are usually found in clusters within craters and their surrounding ejecta, as well as in areas of low reflectance material (LRM), and in association with pyroclastic deposits. Within individual craters, hollow location depends on crater type (simple, complex). At complex craters, hollows occur on proximal ejecta blankets and on the crater walls, floors and central structures. At simple craters, hollows form bands at the tops of crater walls and can extend into the proximal ejecta. Processes through which hollows form on Mercury’s surface, however, are not known, and the volatile phases involved in hollow formation are still speculated on. A better understanding of how hollows form would inform on the volatile budget and internal composition of Mercury, as well as on processes modifying the regolith. In this thesis, I further characterize relationships among the locations of hollows on crater walls, floors, central structures, proximal ejecta and superposed craters and the degradation class of host craters using MESSENGER MDIS image data. I also provide a complete catalogue of superposed craters D > 5 km with hollows within these host craters. My goal is to provide new observational constraints for processes governing the formation, evolution and timing of hollows inside impact craters, as well as on the origin of hollow-forming volatiles within the crust. From this work, I find that the bulk of hollows within an impact crater likely form following the initial impact event, and that subsequent impact cratering drives the formation of following generations of hollows within more degraded craters. Not all superposed craters excavate hollows, however, therefore while the cratering process is an important driver of hollow formation, it is not sufficient by itself. Finally, hollows occurring at superposed craters of all diameters shows that hollow-forming volatiles are present at a range of depths within the crust, including near the surface. I find that surface chemistry or the presence of LRM, which is often excavated at impact craters, do not control the formation of hollows.

Text

2024-05-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88391

Geophysics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/