Browsing by Author "Russell, C."

Dawn FC color images of Vesta reveal unprecedented lithologic detail shown by examples of nonlinear color ratios, which were derived using cluster analysis.

We processed Dawn Framing Camera color filter images to produce global spectral mosaics of 1 Ceres. The mosaics allow analyses of compositional variations of the cerean surface. Moreover, we can derive statements about Ceres' surface absolute reflectivity using photometrically corrected FC data. During EPSC, we will show examples including global mosaics from Survey orbit images.

We report about the most recent results of our olivine mapping of the vestan surface based on Dawn Framing Camera Data.

The Dawn Framing Camera (FC) [1] has imaged the entire visible surface of Vesta from three different orbits at spatial resolutions of ~250 m/pixel, ~60 m/pixel, and ~20 m/pixel. The FC is equipped with one clear and seven color filters, cover-ing the wavelength range between 0.44 and 1.0 µm [1]. Vesta is geologically the most diverse differentiated basaltic asteroid that survived the collisional history of the Solar System [2]. Most of the howardite-eucrite-diogenite meteorites (HEDs) and the Vestoids are be-lieved to be samples from Vesta [3], [4]. Several mod-els, based on the petrogenesis of HEDs [5], [6], favor the evolution of Vesta through a magma ocean. How-ever, the variance of incompatible trace elements among diogenites also supports the serial magmatism model [7], [8]. The recent finding of olivine-rich expo-sures in Bellicia and Arruntia craters in the Northern Hemisphere [9], led to many ambiguities, as well as complexities in understanding the geological evolution of Vesta. Here we present our analyses and observa-tions of two olivine-rich exposures. Spectra of HEDs, olivine-orthopyroxene mixtures, olivines, and high Ca-pyroxenes (HCPs) were acquired from RELAB, HOSERLab and USGS. The olivine diagnostic FC parameters we have developed are: Band Tilt (BT) = (R 0.92µm / R 0.96µm) Mid Ratio (MR) = (R 0.75µm / R 0.83µm) / (R 0.83µm / R 0.92µm) Mid Curvature (MC) = (R 0.75µm + R 0.92µm) / R 0.83µm where R(λ) is the reflectance in the corresponding filter.

The historic journey of the Dawn spacecraft in 2011-2012 was a turning point in understanding asteroid (4) Vesta. The surface composition and lithology were analysed and mapped in earlier studies using Dawn imageries [1], [2]. We introduce here a 3-dimensional spectral approach to analyze and map the surface composition using Dawn Framing Camera (FC) color data. Various laboratory spectra of available HEDs and their mixtures, including new spectra measured in this work, were used. Band parameters were reviewed and modified wherever necessary to make the best use of the data. We particularly focused on carbonaceous-chondrite-bearing and olivine-bearing lithologies. An attempt has been made to distinguish glass/impact-melt lithologies.

We present the results of an extensive mapping effort of the Vestan surface by using Dawn Framing Camera (FC) data. The identified lithologies are of HED, carbonaceous chondritic and peridotitic nature and include specific sites as, for example, the Marcia crater.