The remarkable surface homogeneity of the Dawn mission target (1) Ceres |
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Authors: | Benoît Carry Pierre Vernazza Christophe Dumas William J. Merline Olivier Mousis Philippe Rousselot Emmanuël Jehin Jean Manfroid Marcello Fulchignoni Jean-Marc Zucconi |
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Affiliation: | 1. European Space Astronomy Centre, ESA, P.O. Box 78, 28691 Villanueva de la Cañada, Madrid, Spain;2. LESIA, Observatoire de Paris Meudon – CNRS, 5 place Jules Janssen, 92195 Meudon Cedex, France;3. European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile;4. European Southern Observatory, K. Schwarzschild-Str. 2, 85748 Garching, Germany;5. Laboratoire dAstrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille, France;6. Research and Scientific Support Department, ESA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands;7. Southwest Research Institute, 1050 Walnut St. # 300, Boulder, CO 80302, USA;8. Université de Franche Comté – CNRS, Institut UTINAM, 41 bis av. de l’Observatoire, F-25010 Besançon Cedex, France;9. Institut d’Astrophysique et de Géophysique, Université de Liège, B-4000 Liège, Belgium |
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Abstract: | Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron spectroscopy. While Ceres’ visible and near-infrared disk-integrated spectra have been well characterized, little has been done about quantifying spectral variations over the surface. Any spectral variation would give us insights on the geographical variation of the composition and/or the surface age. The only work so far was that of Rivkin and Volquardsen ([2010], Icarus 206, 327) who reported rotationally-resolved spectroscopic (disk-integrated) observations in the 2.2–4.0 μm range; their observations showed evidence for a relatively uniform surface.Here, we report disk-resolved observations of Ceres with SINFONI (ESO VLT) in the 1.17–1.32 μm and 1.45–2.35 μm wavelength ranges. The observations were made under excellent seeing conditions (0.6″), allowing us to reach a spatial resolution of ~75 km on Ceres’ surface. We do not find any spectral variation above a 3% level, suggesting a homogeneous surface at our spatial resolution. Slight variations (about 2%) of the spectral slope are detected, geographically correlated with the albedo markings reported from the analysis of the HST and Keck disk-resolved images of Ceres (Li et al. [2006], Icarus 182, 143; Carry et al. [2008], Astron. Astrophys. 478, 235). Given the lack of constraints on the surface composition of Ceres, however, we cannot assert the causes of these variations. |
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