Day: April 10, 2017

Meteoritic minerals and their origins

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1,2Alan E. Rubin, 3Chi Ma
Chemie der Erde – Geochemistry (in Press) Link to Article [http://doi.org/10.1016/j.chemer.2017.01.005]
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
2Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA
3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Copyright Elsevier

About 435 mineral species have been identified in meteorites including native elements, metals and metallic alloys, carbides, nitrides and oxynitrides, phosphides, silicides, sulfides and hydroxysulfides, tellurides, arsenides and sulfarsenides, halides, oxides, hydroxides, carbonates, sulfates, molybdates, tungstates, phosphates and silico phosphates, oxalates, and silicates from all six structural groups. The minerals in meteorites can be categorized as having formed by a myriad of processes that are not all mutually distinct: (1) condensation in gaseous envelopes around evolved stars (presolar grains), (2) condensation in the solar nebula, (3) crystallization in CAI and AOI melts, (4) crystallization in chondrule melts, (5) exsolution during the cooling of CAIs, (6) exsolution during the cooling of chondrules and opaque assemblages, (7) annealing of amorphous material, (8) thermal metamorphism and exsolution, (9) aqueous alteration, hydrothermal alteration and metasomatism, (10) shock metamorphism, (11) condensation within impact plumes, (12) crystallization from melts in differentiated or partially differentiated bodies, (13) condensation from late-stage vapors in differentiated bodies, (14) exsolution, inversion and subsolidus redox effects within cooling igneous materials, (15) solar heating near perihelion, (16) atmospheric passage, and (17) terrestrial weathering.

 

Evidence for OH or H2O on the surface of 433 Eros and 1036 Ganymed

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1Andrew S. Rivkin, 2Ellen S. Howell, 3Joshua P. Emery, 4Jessica Sunshine
Icarus (in Press) Link to Article [http://doi.org/10.1016/j.icarus.2017.04.006]
1Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Rd, Laurel MD, 20723 USA 443-778-2811
2University of Arizona, Lunar and Planetary Laboratory
3University of Tennessee
4University of Maryland
Copyright Elsevier

Water and hydroxyl, once thought to be found only in the primitive airless bodies that formed beyond roughly 2.5-3 AU, have recently been detected on the Moon and Vesta, which both have surfaces dominated by evolved, non-primitive compositions. In both these cases, the water/OH is thought to be exogenic, either brought in via impacts with comets or hydrated asteroids or created via solar wind interactions with silicates in the regolith or both. Such exogenic processes should also be occurring on other airless body surfaces. To test this hypothesis, we used the NASA Infrared Telescope Facility (IRTF) to measure reflectance spectra (2.0 to 4.1 μm) of two large near-Earth asteroids (NEAs) with compositions generally interpreted as anhydrous: 433 Eros and 1036 Ganymed. OH is detected on both of these bodies in the form of absorption features near 3 μm. The spectra contain a component of thermal emission at longer wavelengths, from which we estimate thermal of 167±98 J m−2s−1/2K−1 for Eros (consistent with previous estimates) and 214±80 J m−2s−1/2K−1 for Ganymed, the first reported measurement of thermal inertia for this object. These observations demonstrate that processes responsible for water/OH creation on large airless bodies also act on much smaller bodies.