^1,2Thomas B. Leith, ¹Nicholas A. Moskovitz, ³Rhiannon G. Mayne, ⁴Francesca E. DeMeo, ⁵Driss Takir, ^1,4Brian J. Burt, ⁴Richard P. Binzel, ⁴Dimitra Pefkou
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.05.007]
¹Lowell Observatory, Flagstaff, AZ, 86001, USA
²Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, USA
³Monnig Meteorite Collection, Texas Christian University, Fort Worth, TX, 76129, USA
⁴Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
⁵Astrogeology Science Center, United States Geological Survey, Flagstaff, AZ, 86001, USA
Copyright Elsevier

We present near-infrared (0.78-2.45 μm) reflectance spectra for nine middle and outer main belt (a > 2.5 AU) basaltic asteroids. Three of these objects are spectrally distinct from all classifications in the Bus-DeMeo system and could represent spectral end members in the existing taxonomy or be representatives of a new spectral type. The remainder of the sample are classified as V- or R-type. All of these asteroids are dynamically detached from the Vesta collisional family, but are too small to be intact differentiated parent bodies, implying that they originated from differentiated planetesimals which have since been destroyed or ejected from the solar system. The 1- and 2-μm band centers of all objects, determined using the Modified Gaussian Model (MGM), were compared to those of 47 Vestoids and fifteen HED meteorites of known composition. The HEDs enabled us to determine formulas relating Band 1 and Band 2 centers to pyroxene ferrosilite (Fs) compositions. Using these formulas we present the most comprehensive compositional analysis to date of middle and outer belt basaltic asteroids. We also conduct a careful error analysis of the MGM-derived band centers for implementation in future analyses. The six outer belt V- and R-type asteroids show more dispersion in parameter space than the Vestoids, reflecting greater compositional diversity than Vesta and its associated bodies. The objects analyzed have Fs numbers which are, on average, between five and ten molar percent lower than those of the Vestoids; however, identification and compositional analysis of additional outer belt basaltic asteroids would help to confirm or refute this result. Given the gradient in oxidation state which existed within the solar nebula, these results tentatively suggest that these objects formed at either a different time or location than 4 Vesta.

¹Maria Eugenia Varela, ²Ernst Zinner
Geochmica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2017.03.038]
¹ICATE-CONICET, Av. España 1512 Sur, San Juan, Argentina
²Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

The process/es involved in chondrule formation cover a wide range of mechanisms whose nature is still unknown. Our attention is focused on solar nebula processes mainly in untangling the origin of the initial liquid droplets that turn into chondrules. To do this, we start deciphering the processes under which the chondritic constituents of glass-rich, PO and POP chondrules from the Unequilibrated Ordinary Chondrite (UOC) Tieschitz L/H3.6 could have been formed. One constituent is the initial refractory liquid. This chilled liquid, presented as primary glass inclusions in olivine or as glass mesostasis, has trace element abundances with unfractionated patterns and lacks the chemical signature that is expected from a geochemical (liquid-crystal) fractionation. The unfractionated crystal-liquid distribution coefficients observed in the glass-rich, PO and POP chondrules indicate that formation of these objects was not dominated by an igneous process. In addition, the good correlation of elements with different geochemical and cosmochemical properties (e.g., Yb and La-Ce) that spread around the primordial ratio, indicate that a cosmochemical (condensation) instead of a geochemical process may have been involved in the origin of this refractory liquid. We end up discussing a secondary process: the alkali-Ca exchange reaction that could have taken place within a cooling nebula at sub-solidus temperatures. The extent to which these solid/gas exchange reactions took place will determine the final composition of the chondrules.