Antipodal terrains created by the Rheasilvia basin forming impact on asteroid 4 Vesta

Abstract

The Rheasilvia impact on asteroid 4 Vesta may have been sufficiently large to create disrupted terrains at the impact antipode. This paper investigates the amount of deformation expected at the Rheasilvia antipode using numerical models of sufficient resolution to directly observe terrain modification and material displacements following the arrival of impact stresses. We find that the magnitude and mode of deformation expected at the impact antipode is strongly dependent on both the sound speed and porosity of Vesta's mantle, as well as the strength of the Vestan core. In the case of low mantle porosities and high core strengths, we predict the existence of a topographic high (a peak) caused by the collection of spalled and uplifted material at the antipode. Observations by NASA's Dawn spacecraft cannot provide definite evidence that large amounts of deformation occurred at the Rheasilvia antipode, largely due to the presence of younger large impact craters in the region. However, a deficiency of small craters near the antipodal point suggests that some degree of deformation did occur.

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

“…In this second location, the topography is partly the result of the fresh crater Torquata and of a ridge of unit Sfc. The crater Torquata is also located close to the Veneneia antipode (65°N/350°E), where antipodal uplift could be expected (e.g., Bowling et al, 2013;Blewett et al, submitted for publication). The ejecta of the Varronilla basin would need to be unevenly distributed to create an elevated area only near 47°N/62°E and near Torquata.…”

“…The NE-SW ridge that truncates the Postumia basin could have formed by a large-scale fault. North of the fault, part of the Postumia basin may have been lifted up by antipodal effects of the Veneneia or Rheasilvia impacts (e.g., Blewett et al, submitted for publication; Bowling et al, 2013). In-depth analyses and a discussion of the tectonic features that characterize unit Sft are presented by Scully et al (2014).…”

“…Additional lineations could have formed due to impact shock waves (e.g., Bowling et al, 2013;Jutzi et al, 2013a) or shear stresses following the Rheasilvia-forming event (Scully et al, this issue). Alternatively, and at least for some of the lineations linked to an ejecta ray system, the origin is due to impact scouring across the surface (Scully et al, …”

The chronostratigraphy of protoplanet Vesta

“…In addition, Dawn compositional data were compared with the large body of petrologic, geochemical, and geochronologic studies of HED meteorites (e.g., Keil, 2002;McSween et al, 2011, and references therein), which have been demonstrated to have come from Vesta or its associated vestoid family (McSween et al, 2013a). Mathematical computer modeling of large impact events (e.g., Jutzi and Asphaug, 2011;Bowling et al, 2013) has also aided in interpretation of Dawn data.…”

“…Our goal was to identify key geologic events recorded on the surface of Vesta, as recognized through mapping and other studies (e.g., Buczkowski et al, 2012;Bowling et al, 2013), and from them synthesize a timestratigraphic scheme and geologic time scale.…”