Lunar and Planetary Institute
3600 Bay Area Boulevard
Houston, TX 77058
Grabens on Io: Evidence for extensional tectonics
Io may well be the most geologically active body in the solar system. A variety of volcanic features have been identified, including a few fissure eruptions, but tectonism is generally assumed to be limited to compression driven mountain formation. A wide range of structural features can also be identified including scarps, lineaments, faults, and circular depressions (pits and patera rims). Narrow curvilinear graben (elongated, relatively depressed crustal unit or block that is bounded by faults on its sides) are also scattered across Io’s volcanic plains. These features are dwarfed by the more prominent neighboring volcanoes and mountains, and have been largely ignored in the literature. Although they are likely to be extensional in origin, their relationship to local or global stress fields is unknown. We have mapped the locations, length and width of graben on Io using all available Voyager and Galileo images with a resolution better than 5 km. We compare the locations of graben with existing volcanic centers, paterae and mountain data to determine the degree of correlation between these geologic features and major topographic variations (basins/swells) in our global topographic map of Io.
Geologic Mapping of Vesta: I am currently mapping The AV-11 Pinaria Quadrangle of Asteroid 4Vesta. NASA’s Dawn spacecraft entered orbit of the inner main belt asteroid “4Vesta” in July 2011, and is spending one year in orbit to characterize its geology, elemental and mineralogical composition, topography, shape, and internal structure.
Investigation of Secondary Craters in the Saturnian System
At present, surface ages of bodies in the outer solar system are determined only from crater densities (a method dependent on an understanding of the projectile populations responsible for impact craters in these planetary systems). To derive accurate ages using impact craters, the impact source must be determined. Impact craters can be primary, secondary or sesquinary. Primary craters are made by direct impact of comets or asteroids. Secondary craters are produced by impact of ejecta thrown some distance away by a primary impact on that same body. Secondary craters are more heavily influenced by surface mechanical properties than their larger counter parts. Our objective is to better understand the contribution of (dispersed) secondary craters to the small crater population, and thereby ultimately that of small comets to the projectile flux on large icy satellites. In this study we investigate the origin of secondary craters in the larger context. We measure the diameter of obvious secondary craters (determined by irregular crater shape and small size) created by Inktomi (a 48 km diameter crater on Rhea). While focusing on Rhea, we also investigate secondary crater size/frequency/distribution/formation and secondary crater chain formation on icy satellites throughout the Jupiter and Saturn systems.