Spectral Diversity of Ceres' Surface as Measured by VIR
Abstract:The Dawn spacecraft has been acquiring data of dwarf planet Ceres since January 2015(1). In particular, the VIS-IR spectrometer VIR (2) acquired data during approach to Ceres and the first two mapping orbits and it will continue its measurements during the last two mapping orbits(3).
Ceres’ average spectrum is characterized by a prominent absorption band at 2.7 micron and weaker bands in the 3.0-4.0 micron region while the visible and near-IR ranges lack prominent bands. This spectrum is well represented by a mixture of ammoniated phyllosilicates and other clays, Mg-carbonates, and dark material, like magnetite(4).
VIR is observing spectral variability all across the surface of Ceres particularly evident in changes of the shape of the spectra in the range from 0.5 to 4.0 micron. The spectral diversity was already evident in the 11Km/px spectral images from the approach phase(5). The spectral slope in the visual spectral range in addition to the center and depth of the detected absorption bands in the IR range have been computed and mapped. The maps presented here are based on data from Survey orbit acquired in June 2015 with 1.1Km/px of nominal resolution and are the most spatially resolved global view of the surface by VIR. They have been used to study the distribution of the spectral heterogeneities on the surface. The parameters mapped so far, in particular the spectral slope in the VIS range, has a distribution which appears to be associated with impact craters and local events on the surface rather than global processes. The analysis of higher spatial resolution spectra that will be acquired in later phases of the Dawn encounter is needed to confirm this correlation and to provide an interpretation on its role on the evolution of Ceres’ surface.
1)Russell,C.T. et al. Dawn arrives at Ceres: results of Survey orbits,2015,EPSC. 2)De Sanctis,M.C. et al., The VIR Spectrometer,2011,Space Sci. Rev. 3)Ammannito E. et al., Spectral diversity of Ceres surface as measured by VIR,2015,EPSC. 4)De Sanctis,M.C. et al. Ammoniated phyllosilicates on dwarf planet Ceres reveal an outer solar system origin, Nature submitted,2015. 5)Zambon F. et al., Color variations on Ceres derived by Dawn/VIR: Implications for the surface composition,2015,EPSC