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要旨

In this study we investigated the previously observed young resurfacing absolute model ages at the floor of Occator crater on dwarf planet Ceres on the basis of Dawn data. These young resurfacing absolute model ages have been interpreted to represent the deposition of cryovolcanic material >10 Myr after the formation of Occator crater. In our study we investigated whether these resurfacing events are caused by deposition of cryovolcanic material, or if seismic shaking related to the formation or reactivation of prominent fracture systems at the floor of Occator crater might be responsible for the resurfacing. We chose 22 different count areas with differing distances to the fractures and determined absolute model ages of these areas by performing crater size-frequency distribution measurements. Most of our measurements show the formation age of Occator crater (∼21 Ma) as background age, but also different sets of resurfacing ages, varying from 3.7 Ma to 9.2 Ma. A trend towards younger absolute model ages with decreasing distance to fractures is not supported by our data. Thus, we conclude that seismic shaking might not be responsible for the young resurfacing events spread all over the floor of Occator crater. Moreover, our investigations show that target property effects and differing image resolutions do not affect our measurements significantly. Consequently, deposition of young cryovolcanic material seems to be the most plausible geologic process being responsible for the observed young resurfacing ages.