Large impact features on middle-sized icy satellites

Abstract

All of the large impact features of the middle-sized icy satellites of Saturn and Uranus that were clearly observed by the Voyager spacecraft are described. New image mosaics and stereo-and-photoclinometrically-derived digital elevation models are presented. Landforms related to large impact features, such as secondary craters and possible antipodal effects are examined and evaluated. Of the large impacts, Odysseus on Tethys appears to have had the most profound effect on its "target" satellite of any of the impact features we examined. Our modeling suggests that the Odysseus impact may have caused the prompt formation of Ithaca Chasma, a belt of tectonic troughs that roughly follow a great circle normal to the center of Odysseus, although other hypotheses remain viable. We identify probable secondary cratering from Tirawa on Rhea. We attribute a number of converging coalescing crater chains on Rhea to a putative, possibly relatively fresh, ∼ 350 km-diameter impact feature. We examine the antipodes of Odysseus, the putative ∼ 350 km-diameter Rhean impact feature, and Tirawa, and conclude that evidence from Voyager data for damage from seismic focusing is equivocal, although our modeling results indicate that such damage may have occurred. We propose a number of observations and tests for Cassini that offer the opportunity to differentiate among the various explanations and speculations reviewed and evaluated in this study.

Thermal constraints on the early history of the H-chondrite parent body reconsidered

“…However, even larger impacts have been observed to leave their target bodies intact (e.g., Moore et al, 2004). The largest crater on Vesta, for instance, is estimated to have had a transient diameter of $300 km (Asphaug, 1997), about 60% of the Vesta diameter (530 km).…”

Subsurface failure in spherical bodies: A formation scenario for linear troughs on Vesta’s surface

“…Impact-induced failure within a spherical target contrasts with failure in a planar target due to curvature of the surface that focuses shock waves toward the center with incipient (if not total) failure at the farside (e.g., Rinehart, 1960;Gault and Wedekind, 1969). This phenomenon is important even for planetary bodies such as the Moon and Mercury (Schultz and Gault, 1975;Hughes et al, 1977;Schultz and Crawford, 2011), and Saturnian satellites Moore et al, 2004).…”

The large crater on the small Asteroid (2867) Steins

“…The size of such a crater will be a function of several key properties of the body, including its composition and structure. Previous work has looked at impacts on mid-sized icy satellites (diameter 400 -1600 km) for example (Moore et al, 2004), and impacts on smaller rocky bodies (with diameters of order 10 -500 km, e.g. see Thomas 1999).…”