Morphology and scaling of ejecta deposits on icy satellites

Schenk, P.; Ridolfi, Francis J.

doi:10.1029/2001gl013512

Cited by 26 publications

(16 citation statements)

References 10 publications

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“…None of the large impact features we will discuss in this section were imaged by Voyager at sufficient resolution to unequivocally discern their proximal ejecta blanket facies. However, Schenk and Ridolfi (2002) identify probable ejecta deposits of smaller craters on Dione and Rhea with similar rim-scaled dimensions as ejecta deposits on Ganymede and Callisto. Secondaries were also observed at the 80-km crater Yu-ti on Rhea, which was imaged at 1 km pixel −1 and optimum solar incidence angle for landform recognition.…”

Section: Ejecta and Secondariesmentioning

confidence: 85%

Large impact features on middle-sized icy satellites

Moore

Schenk

Bruesch

et al. 2004

Icarus

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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.

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Section: Ejecta and Secondariesmentioning

confidence: 85%

Large impact features on middle-sized icy satellites

Moore

Schenk

Bruesch

et al. 2004

Icarus

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“…The boundary of one of these structures may correspond to the edge of the continuous ejecta, so the initial diameter of the unrelaxed crater could be as much as a factor of ∼2–3 smaller [ Passey and Shoemaker , 1982; Jones et al , 2003; cf. Schenk and Ridolfi , 2002; Schenk et al , 2004]. To relax a crater of that size so significantly would also indicate heat flows in excess of 10 mW m −2 .…”

Section: Discussionmentioning

confidence: 99%

Elastoviscoplastic relaxation of impact crater topography with application to Ganymede and Callisto

Dombard

McKinnon²

2006

J. Geophys. Res.

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[1] We use an elastoviscoplastic rheological model to study the long-term relaxation of impact crater topography on Ganymede and Callisto. We employ a complete set of rheological parameters for ductile creep in ice I h and implement a new, shallower initial shape model. Under high heat flow conditions, stresses are relieved in deeper, less viscous material, and the remainder concentrates as flexural (bending) stresses in a viscously stiffer near-surface layer. Essentially, a mechanical lithosphere forms that focuses stresses but with uplifts and stress levels that are always greater than those obtained for a purely viscous half space. We discuss how classic elastic flexure and purely viscous relaxation are special cases of this more generalized rheological model. Stress concentration in the flexing (i.e., bending) layer can exceed the plastic yield strength of ice for high enough heat flows, weakening the layer somewhat and increasing the total amount of relaxation. These plastic strains tend to be limited to small magnitudes (<0.5%) in a shallow region on the crater floor; such features may be observable in available imagery. The grain size sensitivity of the dominant creep mechanism in ice represents a new input parameter in crater relaxation studies on icy satellites (along with the elastic and plastic moduli, although to a lesser extent). Nevertheless, we find that for reasonable input parameters our simulations reproduce the continuum of relaxation states seen on Ganymede and Callisto. A combination of higher surface temperatures ($120-130 K) and larger grain sizes (>1 mm) permits both retention and relaxation of topography at the lower and higher ends, respectively, of the anticipated heat flow range. Consideration of relaxed craters in Marius Regio and of the palimpsests and penepalimpsests suggests ancient heat flows in excess of 10 mW m À2 , consistent with other estimates.

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“…On Mercury and Mars, it is about 11 and 7 km in diameter, correspondingly, and 2-4 km in diameter on Earth (depending on whether the crater forms in sedimentary or crystalline rocks). On icy satellites, the transition depends on the low-temperature ice strength and the presence or absence of a sub-ice liquid mantle (Moore et al, 2001;Schenk, 2002;Schenk and Ridolfi, 2002;Schenk et al, 2004). Hartmann and Wood (1971) described a broadening of central peaks into ring of peaks, for which they coined the term peak ring.…”

Section: Impact Craters: Morphologymentioning

confidence: 95%