Analysis of the large-scale throughs on Vesta and correlation to a model of giant impact into a differentiated asteroid

Abstract

We evaluate the morphology of large-scale linear structural features observed on the surface Vesta by the Dawn spacecraft [1] to determine what processes caused them to form and what implications this has on the history of Vesta as a planetary body. The dimensions and shape of these features suggest that they are fault-bounded graben similar in size and morphology to those observed on terrestrial planets, as opposed to the fractures and grooves found on smaller asteroids [2]. Their vertical displacement versus length relationship is evaluated to describe and interpret the evolution of the component faults. Linear structures have been identified in concentric orientation around impact craters on several smaller asteroids (e.g. Ida [3], Eros [4], Lutetia [5]), with the formation of these structures tied to the impact event [3, 4]. Although the similar orientation of the Vesta troughs relative to the Rheasilvia and Veneneia basins implies that impact may have been responsible for triggering their formation [1], we suggest that their morphology implies that some other component must also have been involved in their development. It has been established that Vesta is a differentiated body with a core [6]. Preliminary CTH hydrocode [7] models of a 530 km sphere composed of a basalt analog with a 220 km iron core [6] show that the impact of a 50 km object results in different patterns of tensile stress and pressure compared to impact into an undifferentiated sphere of the same material and diameter. While these first-order models have yet to fully mimic the observations we’ve made on Vesta, they do demonstrate that the density contrast in Vesta’s differentiated interior affects the stresses resulting from the Rheasilvia and Veneneia impacts. It is this impedance mismatch that we suggest is responsible for the development of Vesta’s planetary-style troughs. We acknowledge the Dawn Instrument, Operations, and Science Teams and the Dawn at Vesta Participating Science Program.