¹Jean-Philippe Combe et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.12.039]
¹Bear Fight Institute, 22 Fiddler’s Road, P.O. Box 667, Winthrop, WA 98862, USA
Copyright Elsevier

We studied the surface composition of Ceres within the limits of the Ezinu quadrangle in the ranges 180 – 270°E and 21 – 66°N by analyzing data from Dawn’s visible and near-infrared data from the Visible and InfraRed mapping spectrometer and from multispectral images from the Framing Camera. Our analysis includes the distribution of hydroxylated minerals, ammoniated phyllosilicates, carbonates, the search for organic materials and the characterization of physical properties of the regolith. The surface of this quadrangle is largely homogenous, except for small, high-albedo carbonate-rich areas, and one zone on dark, lobate materials on the floor of Occator, which constitute the main topics of investigation. 1) Carbonate-rich surface compositions are associated with H2O ice rich crust. Weaker absorption bands of hydroxylated and ammoniated minerals over the carbonate-rich areas can be explained by higher abundances of carbonates at the topmost surface. 2) Dark, smooth lobate materials at the foot of Occator’s northeastern wall possibly reveal fresh slumping of phyllosilicate-rich materials with fine grain size, or local enrichment in carbon-rich materials such as tholins. 3) The deeper absorption band depth of OH and NH4, on the rim of several impact craters, is one observation that is consistent with a stratification of the phyllosilicate abundance that has been inferred previously from global investigations.

^1,2M.Devogèle et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.12.026]
¹Université de Liège, Space sciences, Technologies and Astrophysics Research (STAR) Institute, Allée du 6 Août 19c, Sart Tilman, 4000 Liège, Belgium
²Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange UMR7293, Nice, France
Copyright Elsevier

Asteroids can be classified into several groups based on their spectral reflectance. Among these groups, the one belonging to the L-class in the taxonomic classification based on visible and near-infrared spectra exhibit several peculiar properties. First, their near-infrared spectrum is characterized by a strong absorption band interpreted as the diagnostic of a high content of the FeO bearing spinel mineral. This mineral is one of the main constituents of Calcium-Aluminum-rich Inclusions (CAI) the oldest mineral compounds found in the solar system. In polarimetry, they possess an uncommonly large value of the inversion angle incompatible with all known asteroid belonging to other taxonomical classes. Asteroids found to possess such a high inversion angle are commonly called Barbarians based on the first asteroid on which this property was first identified, (234) Barbara. In this paper we present the results of an extensive campaign of polarimetric and spectroscopic observations of L-class objects. We have derived phase-polarization curves for a sample of 7 Barbarians, finding a variety of inversion angles ranging between 25 and 30°. Spectral reflectance data exhibit variations in terms of spectral slope and absorption features in the near-infrared. We analyzed these data using a Hapke model to obtain some inferences about the relative abundance of CAI and other mineral compounds. By combining spectroscopic and polarimetric results, we find evidence that the polarimetric inversion angle is directly correlated with the presence of CAI, and the peculiar polarimetric properties of Barbarians are primarily a consequence of their anomalous composition.

¹J.J. Bellucci, ^1,2A.A. Nemchin, ¹M.J. Whitehouse, ¹J.F. Snape, ²P. Bland, ²G.K. Benedix, ³J. Roszjar
Earth and Planetary Science Letters 485, 79-87 Link to Article [https://doi.org/10.1016/j.epsl.2017.12.039]
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05, Stockholm, Sweden
²Department of Applied Geology, Curtin University, Perth, WA 6845, Australia
³Department of Mineralogy and Petrography, Natural History Museum Vienna, Burgring 7, 1010, Vienna, Austria
Copyright Elsevier

The initial Pb compositions of one enriched shergottite, one intermediate shergottite, two depleted shergottites, and Nakhla have been measured by Secondary Ion Mass Spectrometry (SIMS). These values, in addition to data from previous studies using an identical analytical method performed on three enriched shergottites, ALH 84001, and Chassigny, are used to construct a unified and internally consistent model for the differentiation history of the Martian mantle and crystallization ages for Martian meteorites. The differentiation history of the shergottites and Nakhla/Chassigny are fundamentally different, which is in agreement with short-lived radiogenic isotope systematics. The initial Pb compositions of Nakhla/Chassigny are best explained by the late addition of a Pb-enriched component with a primitive, non-radiogenic composition. In contrast, the Pb isotopic compositions of the shergottite group indicate a relatively simple evolutionary history of the Martian mantle that can be modeled based on recent results from the Sm–Nd system. The shergottites have been linked to a single mantle differentiation event at 4504 Ma. Thus, the shergottite Pb isotopic model here reflects a two-stage history 1) pre-silicate differentiation (4504 Ma) and 2) post-silicate differentiation to the age of eruption (as determined by concordant radiogenic isochron ages). The μ-values (²³⁸U/²⁰⁴Pb) obtained for these two different stages of Pb growth are μ₁ of 1.8 and a range of μ₂ from 1.4–4.7, respectively. The μ₁-value of 1.8 is in broad agreement with enstatite and ordinary chondrites and that proposed for proto Earth, suggesting this is the initial μ-value for inner Solar System bodies. When plotted against other source radiogenic isotopic variables (Sr_i, γ¹⁸⁷Os, ε¹⁴³Nd, and ε¹⁷⁶Hf), the second stage mantle evolution range in observed mantle μ  -values display excellent linear correlations (r²>0.85) and represent a spectrum of Martian mantle mixing-end members (depleted, intermediate, enriched).