¹Lucy F. Lim, ^1,2Richard D. Starr, ^1,3Larry G. Evans, ¹Ann M. Parsons, ⁴Michael E. Zolensky, and ⁵William V. Boynton
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12786]

¹NASA Goddard Space Flight Center, Code 691, Greenbelt, Maryland 20771, USA
²Catholic University of America, Washington, District of Columbia 20064, USA
³Computer Sciences Corporation, Lanham-Seabrook, Maryland 20706, USA
⁴ARES, NASA Johnson Space Center, Houston, Texas 77058, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
Published by arrangement with John Wiley & Sons

To evaluate the feasibility of measuring differences in bulk composition among carbonaceous meteorite parent bodies from an asteroid or comet orbiter, we present the results of a performance simulation of an orbital gamma-ray spectroscopy (GRS) experiment in a Dawn-like orbit around spherical model asteroids with a range of carbonaceous compositions. The orbital altitude was held equal to the asteroid radius for 4.5 months. Both the asteroid gamma-ray spectrum and the spacecraft background flux were calculated using the MCNPX Monte-Carlo code. GRS is sensitive to depths below the optical surface (to ≈20–50 cm depth depending on material density). This technique can therefore measure underlying compositions beneath a sulfur-depleted (e.g., Nittler et al. 2001) or desiccated surface layer. We find that 3σ uncertainties of under 1 wt% are achievable for H, C, O, Si, S, Fe, and Cl for five carbonaceous meteorite compositions using the heritage Mars Odyssey GRS design in a spacecraft-deck-mounted configuration at the Odyssey end-of-mission energy resolution, FWHM = 5.7 keV at 1332 keV. The calculated compositional uncertainties are smaller than the compositional differences between carbonaceous chondrite subclasses.

¹Boris Reznik, ¹Agnes Kontny, ²Jörg Fritz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12787]

¹Division of Structural Geology and Tectonophysics, Institute of Applied Geosciences, Karlsruhe Institute of Technology,Karlsruhe, Germany
²Saalbau Weltraum Projekt, Heppenheim, Germany
Published by arrangement with John Wiley & Sons

This study demonstrates a relationship between changes of magnetic susceptibility and microstructure developing in minerals of a magnetite-bearing ore, experimentally shocked to pressures of 5, 10, 20, and 30 GPa. Shock-induced effects on magnetic properties were quantified by bulk magnetic susceptibility measurements while shock-induced microstructures were studied by high-resolution scanning electron microscopy. Microstructural changes were compared between magnetite, quartz, amphibole, and biotite grains. In the 5 GPa sample, a sharp drop of magnetic susceptibility correlates with distinct fragmentation as well as with formation of shear bands and twins in magnetite. At 10 GPa, shear bands and twins in magnetite are accompanied by droplet-shaped nanograins. In this shock pressure regime, quartz and amphibole still show intensive grain fragmentation. Twins in quartz and foam-shaped, highly porous amphibole are formed at 20 and 30 GPa. The formation of porous minerals suggests that shock heating of these mineral grains resulted in localized temperature spikes. The identified shock-induced features in magnetite strongly advise that variations in the bulk magnetic susceptibility result from cooperative grain fragmentation, plastic deformation and/or localized amorphization, and probably postshock annealing. In particular, the increasing shock heating at high pressures is assumed to be responsible for a partial defect annealing which we suggest to be responsible for the almost constant values of magnetic susceptibility above 10 GPa.