Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p21b1597b&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P21B-1597
Physics
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering
Scientific paper
Images returned from the Voyager mission have allowed the analysis of crater morphology on the icy satellites and the construction of both diameter and depth-related scaling laws. Higher resolution Galileo data has since been used to update the diameter-related scaling trends, and also crater depths on the basis of shadow measurements. Our work adds to this wealth of data with new depth and slope information extracted from digital elevation models (DEMs) created from Galileo Solid State Imager (SSI) images, with the use of the stereo scene-recognition algorithm developed by Schenk et al. (2004), and from photoclinometry incorporating the combined lunar-Lambert photometric function as defined by McEwen et al. (1991). We profiled ~80 craters, ranging from 4 km to 100 km in diameter. Once each DEM of a crater was obtained, spurious patterns or shape distortions created by radiation noise or data compression artifacts were removed through the use of standard image noise filters, and manually by visual inspection of the DEM and original image(s). Terrain type was noted during profile collection so that any differences in crater trends on bright and dark terrains could be documented. Up to 16 cross-sectional profiles were taken across each crater so that the natural variation of crater dimensions with azimuth could be included in the measurement error. This already incorporates a systematic error on depth measurements of ~ 5%, an improvement from Voyager depth uncertainties of 10-30%. The crater diameter, depth, wall slope, rim height, central uplift height, diameter and slope, and central pit depth, diameter and slope were measured from each profile. Our measurements of feature diameters and of crater depth are consistent with already published results based on measurement from images and shadow lengths. We will present example topographic profiles and scaling trends, specifically highlighting the new depth and slope information for different crater types on Ganymede. For example: the central peak slopes recorded in our work range from ~ 15° to ~ 2°, increasing as crater diameters increases. In central pit craters, pit slope shows no obvious trend with crater diameter, however, pit slopes do increase linearly with crater depth, crater wall slope and rim height from ~ 2° to ~ 14°. Acknowledgements: This work was funded by Imperial College and by grant #NNX08BA96G from NASA’s Outer Planets Research Program.
Bray Veronica J.
Collins Gary S.
McEwen Alfred S.
Melosh Henry Jay
Morgan Joanna V.
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