Paper No. 8
Presentation Time: 10:45 AM


BUCZKOWSKI, Debra1, WYRICK, Danielle Y.2, YINGST, R. Aileen3, WILLIAMS, David A.4, NATHUES, Andreas5, DESANCTIS, M.C.6, PREUSKER, Frank7 and ROATSCH, Thomas7, (1)Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, (2)Department of Space Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, (3)Planetary Science Institute, 1700 E. Fort Lowell Rd., Suite 106, Tucson, AZ 85719, (4)School of Earth & Space Exploration, Arizona State University, Box 871404, Tempe, AZ 85287, (5)Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, Goettingen, 37077, Germany, (6)Istituto di Astrofisica Spaziale e Fisica Cosmica, Area Ricerca - Roma 2 Tor Vergata, Via Fosso del Cavaliere, 100, Rome, 00133, Italy, (7)German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstr. 2, Berlin, 12489, Germany,

The Av-9 Numisia quadrangle is located in the equatorial region of Vesta, extending from ±22° latitude and from 216º - 288º E longitude (Claudia sytem). Clear filter (monochrome) Framing Camera (FC) Low-Altitude Mapping Orbit (LAMO) images (spatial resolution ~20-25 m/p) were mosaicked to make the quadrangle base. Topography of Av-9 is observed in a colororized Digital Terrain Model derived from Survey orbit FC data. Variations in surface composition are revealed by Visible & Infrared Spectrometer (VIR) hyperspectral images from Survey (700 m/p) and Low-Altitude Mapping Orbit (HAMO) (200 m/p) and FC color ratio images (250 m/p) from Survey orbit.

The Av-9 Numisia quadrangle on Vesta is dominated by Vestalia Terra (VT), a high albedo, topographically high region bound by steep scarps. FC color ratio images using standard Clementine ratios [Red (750/430 nm); Green (750/920 nm); Blue (430/750 nm)] show compositional variations within VT. Further evaluation with VIR identified deposits of OH and diogentite against a primarily howarditic background. Crater counts of southern VT suggest an age similar to the other cratered highlands on Vesta. However, the plateau is cut on all sides by ancient basins and superposition principles thus indicate that the plateau is significantly older than the crater counting would suggest.

While the other equatorial quadrangles on Vesta display numerous wide and flat-floored troughs, Av-9 does not. There are, however, three large pit crater chains: Robigalia and Albalonga Catena, and an unnamed feature. Component merged pits show signs of collapse but distinct fault faces can also be observed. This suggests subsurface faulting of VT.

A feature unique to Av-9 is the “dark ribbon”, a roughly linear unit of albedo-dark material crossing VT from the northwest to the southeast. The ribbon is cut by Numisia crater, whose wall stratigraphy thus exposes the depth of the dark ribbon material. It has been suggested that the dark ribbon is ejecta from Drusilla crater, but the ribbon extends more than 7 crater radii from Drusilla, an OH-bearing crater. It has been hypothesized that the great extent of the dark ribbon is due to a combination of basal glide (ejecta “floating” over impact-released gases) and channelized flow (ejecta entrained within a linear topographic low on top of the VT plateau).