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Asteroid 4 Vesta is currently observed by NASA's Dawn orbiter. The Dawn Team is conducting mineralogical mapping of the surface in the form of 15 quadrangle maps, and here we report results from the mapping of the two adjacent quadrangles Marcia (Av-8) and Numisia (Av-9). The mapping is based on a Framing Camera (FC) color band ratio and Visible and InfraRed (VIR) hyperspectral images. Av-8 Marcia Quadrangle covers 144˚-216˚E longitude while Av-9 Numisia extends from 216˚-288˚E longitude; both quadrangles are located in the equatorial region from ±21˚ latitude. Av-8 Marcia is dominated by a cratered regions, which is a low-albedo ejecta field containing craters Marcia, (68 km by 58 km), Calpurnia (54 km by 52 km), and Minucia (26 km by 23 km). A hill with a dark-rayed crater, named Aricia Tholus, is also nearby (size about 42.5 km and 28 km). Av-9 Numisia is dominated by Vestalia Terra, a distinct region of Vesta. Many of the impact craters in Av-9 have both bright and dark layers in their walls and also distinct ejecta lobes. The largest feature in Av-9 is the 33 km diameter Numisia crater which is centrally located at 7°S, 247°E. The other significant feature is the 15 km diameter Cornelia crater. Cornelia, smaller than Numisia is apparently more interesting has it shows a greater color diversity and an extensive ray system. In particular FC color data show an inner dark albedo region surrounded by an extended light colored ray system, this is also shown in the VIR images. Both FC color ratio images and VIR images show compositional variations within the Marcia quadrangle (De Sanctis et al., LPSC2012). The band depth distribution is uneven in this region and associated with the geological structures present in the quadrangles. On average the dominant terrains are the so called ET ( Equatorial Terrains) characterized by intermediate band depths, but associated with Marcia we see also terrains with very deep band depth similar to the ST (Southern Terrains) and deep band depth as the MLT (Mid Latitude Terrains). The low albedo ejecta field, derived from the Marcia and Calpurnia craters (located in Av-9), mantles underlying older terrains and is associated with the CET (Copious ejecta Terrains): the band depth are very shallow. VIR data show strong 1 µm and 2 µm absorptions exposed within the walls and floor of impact crater Marcia, suggesting excavation of pyroxene-rich material and/or variations in particle sizes. FC color ratio images, as well as VIR color ratio (Red:750/430 nm; Green :750/920 nm; Blue:430/750 nm) show color differences in Marcia and Calpurnia. The color and spectral data show the difference between the eastern side of the Marcia and Calpurnia ejecta field from its western side. Moreover it appears an unusual diffuse deposit surrounding an unnamed crater on the western side of the quadrangle. Further study is underway to investigate the significance of these color variations. The authors gratefully acknowledge the support of the Dawn Instrument, Operations, and Science Teams. This work is supported by an Italian Space Agency (ASI) grant and by NASA through the Dawn project and a Dawn at Vesta Participating Scientist grant.

Asteroid 4 Vesta is currently under investigation by NASA's Dawn orbiter. The Dawn Science Team is conducting mineralogical mapping of Vesta's surface in the form of 15 quadrangle maps, and here we report results from the mapping of Floronia quadrangle Av-5. The maps are based on the data acquired by the Visible and Infrared Mapping Spectrometer (VIR-MS) and the Framing Camera (FC) (De Sanctis et al., this meeting). This abstract is focused on the analysis of band ratios, as well as the depth and position of the 2-µm absorption band of pyroxenes, but additional information will be presented. Absorption band depth is sensitive to abundance, texture and multiple scattering effects. Absorption band position is controlled by composition, shorter wavelength positions indicate less Calcium (and more Magnesium) in pyroxenes. The inferred composition is compared with that of Howardite, Eucite and Diogenite meteorites (HEDs). Diogenites are Mg-rich with large orthopyroxene crystals suggesting formation in depth; Eucrites are Ca-poor pyroxene, with smaller crystals. Av-5 Floronia Quadrangle is located between ~20-66˚N and 270˚-360˚E. It covers a portion of the heavily-cratered northern hemisphere of Vesta, and part of it is in permanent night, until August 2012. Long shadows make the visualization of albedo variations difficult, because of limited effectiveness of photometric corrections. Most of the variations of the band depth at 2 µm are partly affected by illumination geometry in this area. Only regional tendencies are meaningful at this time of the analysis. The 2-µm absorption band depth seems to be deeper towards the south of the quadrangle, in particular to the south of Floronia crater. It is not possible to interpret the value of the band depth in the floor the craters because of the absence of direct sunlight. However, the illuminated rims seem to have a deeper 2-µm absorption band, as does the ejecta from an unnamed crater located further south, within quadrangle Av-10 (Tosi et al., 2010, this meeting). The absorption band seems slightly shifted towards shorter wavelengths in the neighborhood of the same crater, which may indicate a more diogenitic composition, consistent with materials of the deeper crust. Relationships between craters, ejecta and composition will be investigated further. The authors acknowledge the support of the Dawn Science, Instrument and Operations Teams. This work was supported by the NASA Dawn Project under contract from UCLA and by the NASA Dawn at Vesta Participating Scientist program.

Vesta has been hammered by large impacts, including two large (400-500 km) basins at the South Pole, the largest basins in proportion to target radius so far seen in the solar system. Here we examine the global effects of impacts at planetary scales.

Unusual deposits of “Dark Material” (DM) on Vesta’s surface were recently discovered by the Dawn Mission [1,2]. A focused study of these deposits is underway within the Dawn team and the three preceeding presentations in this session [3,4,5] treat different aspects (geological, morphological and compositional) of the Dawn observations analysis. This report is a synthesis of these findings, presents some further analysis and interprets them in terms of origin( s) and processes.

NASA’s Dawn spacecraft began orbiting the inner main belt asteroid 4 Vesta on July 16, 2011, and will characterize the geology, elemental and mineralogical composition, topography, and internal structure of Vesta before departing for asteroid 1 Ceres in late 2012. As part of the Dawn data analysis, the science team is constructing geological mapping of the surface, in the form of 15 quadrangle maps. This abstract reports preliminary results from mapping of quadrangle Av-3, named for Caparronia crater.

Before Dawn arrived at 4 Vesta only very low spatial resolution (~50 km) albedo and color maps were available from HST data. Also ground-based color and spectroscopic data were utilized as a first attempt to map Vesta’s mineralogical diversity [1-4]. The VIR spectrometer [5] onboard Dawn has ac-quired hyperspectral data while the FC camera [6] ob-tained multi-color data of the Vestan surface at very high spatial resolutions, allowing us to map complex geologic, morphologic units and features. We here re-port about the results obtained from a preliminary global mineralogical map of Vesta, based on data from the Survey orbit. This map is part of an iterative map-ping effort; the map is refined with each improvement in resolution.

NASA’s Dawn spacecraft entered orbit of the inner main belt asteroid 4 Vesta on July 16, 2011, and is spending one year in orbit to characterize the geology, chemical and mineralogical composition, topography, shape, and internal structure of Vesta before departing to asteroid 1 Ceres in late 2012. As part of the Dawn data analysis the Science Team is conducting geological mapping of the surface, in the form of 15 quadrangle maps. This abstract reports results from the mapping of quadrangle Av-8, named Marcia. Data: The base for mapping this quadrangle is a monochrome Framing Camera (FC) mosaic produced from the High Altitude Mapping Orbit (HAMO) data with a spatial resolution of ~70 m/pixel. This base is supplemented by a Digital Terrain Model (DTM) derived from Survey orbit stereo image data with a lateral spacing of 450 m/pixel (10 pixels per degree) and a vertical accuracy of ~30 meters. Also used to support the mapping are FC color ratio images from the Survey orbit with a spatial resolution of ~250 m/pixel, slope and contour maps derived from the DTM, and Visible and InfraRed (VIR) hyperspectral images from the Survey and HAMO orbits with spatial resolutions of 700 and 200 m/pixel, respectively.