Impact features on Europa: rheological and thermal states of the icy crust.

The depth of the brittle-ductile transition has been estimated under each g raben rounding two ancient impact basins on Europa, Callanish and Tyre. Sur face thermal gradients have been computed and are respectively equal to 4.3 +/- 0.4 and 2.4 +/- 0.25 K.km(-1). These results differ strongly from prev ious works obtained on other Europa's features. This can be explained by th e variation of both the icy grain size and the chemical composition of the crust, but also by the variation of the local deformation rate, a 2001 Acad emie des sciences / Editions scientifiques et medicales Elsevier SAS.