¹Patrick Michel, ²Martin Jutzi, ³Derek C. Richardson, ⁴Cyrena A. Goodrich, ⁴William K. Hartmann, ⁴David P. O’Brien
¹Laboratoire Lagrange, Université de Nice-Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS 34229, 06304 Nice, Cedex 4, France
²Physics Institute, Space Research and Planetary Sciences Center for Space and Habitability, University of Bern, Switzerland
³Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁴Planetary Science Institute, 1700 E. Ft. Lowell, Tucson, AZ 85719, USA

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Reference
Michel P, Jutzi M, Richardson DC, Goodrich CA, Hartmann WK, O’Brien DP (2014) Selective sampling during catastrophic disruption: Mapping the location of reaccumulated fragments in the original parent Body. Planetary and Space Science (in Presss)
Link to Article [DOI: 10.1016/j.pss.2014.08.005]

¹Paul S. Hardersen, ²Vishnu Reddy, ³Rachel Roberts, ⁴Amy Mainzer
¹University of North Dakota, Department of Space Studies, 4149 University Avenue, Stop 9008, 530 Clifford Hall, Grand Forks, North Dakota, USA 58202-9008
²Planetary Science Institute, 1700 E. Fort Lowell Road, Suite 106, Tucson, Arizona, USA 85719
³University of North Dakota, Department of Space Studies, 4149 University Avenue, Stop 9008, 521 Clifford Hall, Grand Forks, North Dakota, USA 58202-9008
⁴Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California, USA 91109

Vestoids are generally considered to be fragments from Asteroid (4) Vesta that were ejected by past collisions that document Vesta’s collisional history. Dynamical Vestoids are defined by their spatial proximity with Vesta (). Taxonomic Vestoids are defined as V-type asteroids that have a photometric, visible-wavelength spectral, or other observational relationship with Vesta (). We define ‘genetic Vestoids’ as V-type asteroids that are probable fragments ejected from (4) Vesta based on the supporting combination of dynamical, near-infrared (NIR) spectral, and taxonomic evidence. NIR reflectance spectroscopy is one of the primary ground-based techniques to constrain an asteroid’s major surface mineralogy (). Despite the reasonable likelihood that many dynamical and taxonomic Vestoids likely originate from Vesta, ambiguity exists concerning the fraction of these populations that are from Vesta as compared to the fraction of asteroids that might not be related to Vesta.
Currently, one of the most robust techniques to identify the genetic Vestoid population is through NIR reflectance spectroscopy from ∼0.7-2.5 μm. The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite-Eucrite-Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the overall current abundance of basaltic material in the main asteroid belt ().
This work reports high-quality NIR spectra, and their respective interpretations, for eight Vp-type asteroids, as defined by , that were observed at the NASA Infrared Telescope Facility on January 14, 2013 UT. They include: (3867) Shiretoko, (5235) Jean-Loup, (5560) Amytis, (6331) 1992 FZ1, (6976) Kanatsu, (17469) 1991 BT, (29796) 1999 CW77, and (30872) 1992 EM17. All eight asteroids exhibit the broad ∼0.9- and ∼1.9-μm mineral absorption features indicative of pyroxene on each asteroid’s surface. Data reduction and analysis via multiple techniques produced consistent results for the derived spectral absorption band centers and average pyroxene surface chemistries for all eight asteroids (). (3867) Shiretoko is most consistent with the eucrite meteorites while the remaining seven asteroids are most consistent with the howardite meteorites. The existing evidence suggests that all eight of these Vp-type asteroids are genetic Vestoids that probably originated from Vesta’s surface.

Reference
Hardersen PS, Reddy V, Roberts R, Mainzer A (2014) More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.020]

Copyright Elsevier

^1,2Sheridan E. Ackissa, ³J.J. Wray
¹School of Mathematics, Georgia Institute of Technology, Atlanta, GA 30332
²Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723
³School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332

Hydrated sulfate minerals record the history of water and habitable environments on Mars, yet prior studies of them have neglected a vast region surrounding the planet’s south pole. Some of the few sulfates reported there are localized to putative ancient volcanoes that may have erupted under an ice sheet, possibly forming sulfates via hydrothermal alteration. Alternatively, sulfates may have formed more recently from sunlight causing minor melting of polar ices and the weathering of embedded dust particles, a process thought to explain the sulfates found near Mars’s north pole. To test these hypotheses, we searched for southern high-latitude sulfates using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO), focusing on regions that include putative volcanoes or geologically similar landforms. In 217 targeted images, we used spectral parameters to identify regions of interest from which we extracted spectra. The spectra were then visually compared to laboratory spectra to identify possible hydrated mineral constituents. In this paper, we present spectra from 16 of the images and statistics derived from the full set of 217, along with spectra from one mapping tile. We find that hydrated sulfates are found throughout the southern high latitudes suggesting a ubiquitous process for hydrated mineral formation and/or the relocation of hydrated minerals due to a long history of impacts, aeolian transport, weathering and periglacial processes.

Reference
Ackissa SE, Wray JJ (2014) Occurrences of possible hydrated sulfates in the southern high latitudes of Mars. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.016]

Copyright Elsevier

¹Ottaviano Ruesch et al. (>10)*
¹Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, Germany
*Find the extensive, full author and affiliation list on the publishers Website

The magmatism characterizing the early history of the asteroid Vesta has long been investigated with the mafic and ultramafic meteorites howardite, eucrite and diogenite (HED). The lack of geologic context for the meteorites, however, has limited its understanding. Here we use the visible to near-IR (VIR/Dawn) orbital observations of Vesta’s surface to detect relative enrichments in olivine and to study the associated geologic features. Because the near-IR signature of olivine on Vesta’s surface is subtle relative to the widespread pyroxene absorption bands, a method was developed to distinguish olivine enrichments from admixture of pyroxenes with high Fe2+/M1, dark material, and potential Fe-bearing glass. Relative enrichment of olivine (<~50-60 vol%) is found in 2–5 km wide, morphologically fresh areas. Our global survey reveals a dozen of these areas clustering in the eastern hemisphere of Vesta. The hemispherical coincidence with a widespread, low enrichment in diogenite-like pyroxene suggests the presence of a distinct compositional terrain. On the central mound of the Rheasilvia impact basin, no olivine enrichment was found, suggesting the absence of an olivine-dominated mantle above the basin’s excavation depth or, alternatively, a low amount of olivine homogeneously mixed with diogenite-like pyroxenes. Rare olivine-enriched areas in close proximity to diogenite-like pyroxene are found as part of material ejected by the Rheasilvia impact. Such co-occurrence is reminiscent of local, ultramafic lithologies within the crust. The possible formation of such lithologies on Vesta is supported by some HED meteorites dominated by olivine and orthopyroxene.

Reference
Ruesch et al. (2014) Detections and geologic context of local enrichments in olivine on Vesta with VIR/Dawn data. Journal of Geophysical Research: Planets (in Press)
Link to Article [10.1002/2014JE004625]

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