| アブストラクト |
Impact craters on icy satellites display a wide range of morphologies, some of which have no counterpart on rocky bodies. Numerical simulation studies have struggled to reproduce the diversity of features, such as central pits and transitions in crater depth with increasing diameter, observed on the icy satellites around Jupiter. The transitions in crater depth (at diameters of about 26 and 150 km on Ganymede and Callisto) have been interpreted as reflecting subsurface structure. I will present models of the formation of craters with diameters between 400 m and about 200 km on Ganymede using different subsurface temperature profiles. The calculations include recent improvements in the model equation of state for H2O and quasi-static strength parameters for ice. The shock-induced formation of dense high-pressure polymorphs (ices VI and VII) creates a gap in the crater excavation flow, which I call discontinuous excavation. For craters larger than about 20 km, discontinuous excavation concentrates a hot plug of material (>270 K and mostly on the melting curve) in the center of the crater floor. The size and occurrence of the hot plug are in good agreement with the observed characteristics of central pit craters, suggesting that a genetic link exists between them. I will present depth vs. diameter curves for different internal temperature profiles and discuss the implications for subsurface structure.
Reading:
Modeling the morphological diversity of impact craters on icy satellites by L. E. Senft and S. T. Stewart, Icarus, in revision, 2009. |
