T152 The Geology of Asteroid 4 Vesta as Seen by Dawn: Results from One Year in Orbit

Tuesday, 6 November 2012
8:00 AM - 12:00 PM
213D

THE GEOLOGY OF THE VESTALIA TERRA REGION OF ASTEROID VESTA: AN INTEGRATED MAPPING STUDY

Paper number: T152-11
Program: Technical Sessions
Time: 10:45 AM – 11:00 AM

Authors

Abstract

Geologic mapping based on data acquired by the Dawn spacecraft was utilized as a tool to understand the geologic relationships in the Av-9 Numisia quadrangle of the asteroid Vesta. This quadrangle is dominated by Vestalia Terra (VT), a distinct region that is topographically high, bound by steep scarps and albedo-bright. The large number of craters with “colorful” ejecta and bright and/or dark layers displayed in their walls implies that VT is compositionally diverse. Although the VT surface is of intermediate age [1], stratigraphic relationships with the features that form the boundary scarps (ex. Rheasilvia, Saturnalia Fossa, Ferralia basin, degraded basin to north) suggest that the plateau itself may be one of the oldest features on Vesta.

A positive Bouguer gravity anomaly corresponding to VT has been identified [2], suggesting that the materials comprising the plateau have a higher density than the surrounding terrain. This is consistent with VT not displaying any of the numerous wide and flat-floored troughs evident in the other equatorial regions of Vesta [3]. However, there are three long pit crater chains that are roughly aligned with the equatorial troughs. The merged pits show signs of collapse but distinct fault faces can also be observed. A strong correlation between pit crater chains and fault-bounded graben has been observed on other planetary bodies [4]. We suggest that while the equatorial fracturing event may not have been strong enough to completely fracture the dense VT plateau, subsurface fracturing did occur.

The topography of Av-9 reveals the presence of an elongate hill aligned with one of the VT pit crater chains. FC and VIR data show material of a distinct composition which appears to be moving downslope on the northern flank of the hill. Other downslope features include a linear arrangement of elongate pits that may represent a collapsed lava tube. Teia crater impacts the northern face of the hill and its ejecta is albedo-bright and “colorful”, with a distinct “glassy” texture. We suggest that the subsurface fracturing postulated above may have served as a conduit for the VT-unique material to move toward the surface as a dike.

[1] Marchi et al. 2012, Science 336, 690-693 [2] Raymond et al. 2012, ACM abs. #6456 [3] Buczkowski et al. 2012, GRL, submitted [4] Wyrick et al. 2004, JGR doi:10.1029/2004JE 002240