¹A.Raponi et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.02.001]
INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, Rome I-00133, Italy
Copyright Elsevier

Occator Crater on dwarf planet Ceres hosts the so-called faculae, several areas with material 5 to 10 times the albedo of the average Ceres surface: Cerealia Facula, the brightest and largest, and several smaller faculae, Vinalia Faculae, located on the crater floor. The mineralogy of the whole crater is analyzed in this work. Spectral analysis is performed from data of the VIR instrument on board the Dawn spacecraft. We analyse spectral parameters of all main absorption bands, photometry, and continuum slope. Because most of the absorption features are located in a spectral range affected by thermal emission, we developed a procedure for thermal removal. Moreover, quantitative modeling of the measured spectra is performed with a radiative transfer model in order to retrieve abundance and grain size of the identified minerals. Unlike the average Ceres surface that contains a dark component, Mg–Ca-carbonate, Mg-phyllosilicates, and NH4-phyllosilicates, the faculae contain mainly Na-carbonate, Al-phyllosilicates, and NH4-chloride. The present work establishes unambiguously the presence of NH4-chloride thanks to the high-spatial resolution data. Vinalia and Cerealia Faculae show significant differences in the concentrations of these minerals, which have been analyzed. Moreover, heterogeneities are also found within Cerealia Facula that might reflect different deposition events of bright material. An interesting contrast in grain size is found between the center (10–60 µm) and the crater floor/peripheral part of the faculae (100–130 µm), pointing to different cooling time of the grains, respectively faster and slower, and thus to different times of emplacement. This implies the faculae formation is more recent than the crater impact event, consistent with other observations reported in this special issue. For some ejecta, we derived larger concentrations of minerals producing the absorption bands, and smaller grains with respect to the surrounding terrain. This may be related to heterogeneities in the material pre-existent to the impact event.

^1,2Quinn R. Shollenberger, ²Lars E. Borg, ¹Jan Render, ¹Samuel Ebert, ¹Addi Bischoff, ³Sara S. Russell, ¹Gregory A. Brennecka
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.02.006]
¹Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, Münster 48149 Germany
²Nuclear & Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue L-231, Livermore, CA 94550 USA
³Department of Earth Sciences, Natural History Museum, Cromwell Road, Kensington, London SW7 5BD, UK
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials in the Solar System and numerous previous studies have revealed nucleosynthetic anomalies relative to terrestrial rock standards in many isotopic systems. However, most of the isotopic data from CAIs has been limited to the Allende meteorite and a handful of other CV3 chondrites. To better constrain the isotopic composition of the CAI-forming region, we report the first Sr, Mo, Ba, Nd, and Sm isotopic compositions of two CAIs hosted in the CK3 desert meteorites NWA 4964 and NWA 6254 along with two CAIs from the CV3 desert meteorites NWA 6619 and NWA 6991. After consideration of neutron capture processes and the effects of hot-desert weathering, the Sr, Mo, Ba, Nd, and Sm stable isotopic compositions of the samples show clearly resolvable nucleosynthetic anomalies that are in agreement with previous results from Allende and other CV meteorites. The extent of neutron capture, as manifested by shifts in the observed ¹⁴⁹Sm-¹⁵⁰Sm isotopic composition of the CAIs is used to estimate the neutron fluence experienced by some of these samples and ranges from 8.40×10¹³ to 2.11×10¹⁵ n/cm². Overall, regardless of CAI type or host meteorite, CAIs from CV and CK chondrites have similar nucleosynthetic anomalies within analytical uncertainty. We suggest the region that CV and CK CAIs formed was largely uniform with respect to Sr, Mo, Ba, Nd, and Sm isotopes when CAIs condensed and that CAIs hosted in CV and CK meteorites are derived from the same isotopic reservoir.