^1,2Melissa A. Morris, ³Laurence A. J. Garvie, ²L. Paul Knauth
¹State University of New York, Cortland, NY 13045, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
³Center for Meteorite Studies, Arizona State University, Tempe, AZ 85287, USA

Many aspects of planet formation are controlled by the amount of gas remaining in the natal protoplanetary disks (PPDs). Infrared observations show that PPDs undergo a transition stage at several megayears, during which gas densities are reduced. Our Solar System would have experienced such a stage. However, there is currently no data that provides insight into this crucial time in our PPD’s evolution. We show that the Isheyevo meteorite contains the first definitive evidence for a transition disk stage in our Solar System. Isheyevo belongs to a class of metal-rich meteorites whose components have been dated at almost 5 Myr after formation of Ca, Al-rich inclusions, and exhibits unique sedimentary layers that imply formation through gentle sedimentation. We show that such layering can occur via the gentle sweep-up of material found in the impact plume resulting from the collision of two planetesimals. Such sweep-up requires gas densities consistent with observed transition disks (10−12–10−11 g cm−3). As such, Isheyevo presents the first evidence of our own transition disk and provides new constraints on the evolution of our solar nebula.

Reference
Morris MA, Garvie LAJ, Knauth LP (2015) New Insight into the Solar System’s Transition Disk Phase Provided by the Metal-rich Carbonaceous Chondrite Isheyevo. Astrophysical Journal 801 L22.
Link to Article [doi:10.1088/2041-8205/801/2/L22]

¹Daniel Ozdín et al. (>10)*
¹Department of Mineralogy and Petrology, Faculty of Natural Sciences, Comenius University, Bratislava, Slovak Republic
*Find the extensive, full author and affiliation list on the publishers website

The Košice meteorite was observed to fall on 28 February 2010 at 23:25 UT near the city of Košice in eastern Slovakia and its mineralogy, petrology, and geochemistry are described. The characteristic features of the meteorite fragments are fan-like, mosaic, lamellar, and granular chondrules, which were up to 1.2 mm in diameter. The fusion crust has a black-gray color with a thickness up to 0.6 mm. The matrix of the meteorite is formed mainly by forsterite (Fo80.6); diopside; enstatite (Fs16.7); albite; troilite; Fe-Ni metals such as iron and taenite; and some augite, chlorapatite, merrillite, chromite, and tetrataenite. Plagioclase-like glass was also identified. Relative uniform chemical composition of basic silicates, partially brecciated textures, as well as skeletal taenite crystals into troilite veinlets suggest monomict breccia formed at conditions of rapid cooling. The Košice meteorite is classified as ordinary chondrite of the H5 type which has been slightly weathered, and only short veinlets of Fe hydroxides are present. The textural relationships indicate an S3 degree of shock metamorphism and W0 weathering grade. Some fragments of the meteorite Košice are formed by monomict breccia of the petrological type H5. On the basis of REE content, we suggest the Košice chondrite is probably from the same parent body as H5 chondrite Morávka from Czech Republic. Electron-microprobe analysis (EMPA) with focused and defocused electron beam, whole-rock analysis (WRA), inductively coupled plasma mass and optical emission spectroscopy (ICP MS, ICP OES), and calibration-free laser induced breakdown spectroscopy (CF-LIBS) were used to characterize the Košice fragments. The results provide further evidence that whole-rock analysis gives the most accurate analyses, but this method is completely destructive. Two other proposed methods are partially destructive (EMPA) or nondestructive (CF-LIBS), but only major and minor elements can be evaluated due to the significantly lower sample consumption.

Reference
Ozdín D et al. (2015) Mineralogy, petrography, geochemistry, and classification of the Košice Meteorite. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12405]

Published by arrangement with John Wiley&Sons