¹F. Tosi et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Quadrangle Av-10 ‘Oppia’ is one of five quadrangles that cover the equatorial region of asteroid (4) Vesta. This quadrangle is notable for the broad, spectrally distinct ejecta that extend south of the Oppia crater. These ejecta exhibit the steepest (‘reddest’) visible spectral slope observed across the asteroid and have distinct color properties as seen in multispectral composite images. Compared to previous works that focused on the composition and nature of unusual (‘orange’) ejecta found on Vesta, here we take into account a broader area that includes several features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR). Our analysis shows that the older northern and northeastern part of Av-10 is dominated by howardite-like material, while the younger southwestern part, including Oppia and its ejecta blanket, has a markedly eucritic mineralogy. The association of the mineralogical information with the geologic and topographic contexts allows for the establishment of relationships between the age of the main formations observed in this quadrangle and their composition. A major point of interest in the Oppia quadrangle is the spectral signature of hydrous material seen at the local scale. This material can be mapped by using high-resolution VIR data, combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Hydrated mineral phases studied previously on Vesta generally correlate with low-albedo material delivered by carbonaceous asteroids. However, our analysis shows that the strongest OH signature in Av-10 is found in a unit west of Oppia, previously mapped as ‘light mantle material’ and showing moderate reflectance and a red visible slope. With the available data we cannot yet assess the presence of water in this material. However, we offer a possible explanation for its origin.

Reference
Tosi F et al. (2015) Mineralogical analysis of the Oppia quadrangle of asteroid (4) Vesta: Evidence for occurrence of moderate-reflectance hydrated Minerals. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.018]

Copyright Elsevier

¹M.C. De Sanctis et al. (>10*)
¹INAF, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, 00133 Roma, Italy
We currently do not have a copyright agreement with this publisher and cannot display the abstract here

The equatorial Marcia quadrangle region is characterized by the large, relatively young impact craters Marcia and Calpurnia and their surrounding dark ejecta field, a hill with a dark-rayed crater named Aricia Tholus, and an unusual diffuse material surrounding the impact crater Octavia. The spectral analysis indicates that while this region is relatively uniform in the pyroxene band centers, it instead shows large differences in pyroxene band depths and reflectance. A large variation of reflectance is seen in the quadrangle: bright and dark materials are present as diffuse material, and as concentrated spots and outcrops. Moreover, OH signature is pervasive in the quadrangle, with a few exceptions. The region, especially the Marcia ejecta field, is characterized by spectra showing the 2 μm band shifted at long wavelenghts. This is commonly associated with eucritic material, believed to have crystallized as lava on Vesta’s surface or within relatively shallow-level dikes and plutons, thus suggesting that this region is a remnant of the old Vestan basaltic crust. However, other characteristics of the spectra do not fully fit the eucritic composition, indicating an alternative explanation for the band center distribution, including the presence of carbonaceous chondritic material mixed with the native Vestan pyroxene.
The detailed mineralogical analysis of the Marcia quadrangle indicates that this quadrangle is the result of the mixture of the Vestan “endogenic” minerals with the “exogenic” carbonaceous chondrites. The stratigraphic units around Marcia clearly show the bright, uncontaminated material interlaced and mixed with the dark material that contains a strong OH signature. Only few small areas can be considered as representative of the old Vestan original material.

Reference
De Sanctis MC et al. (2015) Eucritic crust remnants and the effect of in-falling hydrous carbonaceous chondrites characterizing the composition of Vesta’s Marcia Region. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.014]

Copyright Elsevier