Nitrogen isotopic compositions in three Antarctic and two non-Antarctic eucrites

Nitrogen isotopic compositions were determined with stepped combustion method for three Antarctic eucrites (Allan Hills-76005,Yamato (Y)-792510 and -82066) and two non-Antarctic eucrites (Juvinas and Camel Donga). The abundances of indigenous nitrogen in these eucrites are from 0.05 to 1.3ppm, much lower than that in ordinary chondrites. The less abundance of nitrogen for eucrites is due to thermal events on the parent body. Isotopic ratios of the trapped nitrogen are also considered. Contribution of terrestrial nitrogen (δ^N from 0‰ to +20‰) and cosmogenic nitrogen (δ^N>+100‰) is significant in the case of eucrites at low temperature (1000℃) fractions, respectively. Hence, nitrogen released at medium temperature fractions is considered. The observed minimum δ^N values released in medium temperature fractions of Y-792510 and Camel Donga are -54‰ and -18‰, respectively. The low δ^N values cannot be explained by contribution of the terrestrial and cosmogenic components. This is strong evidence for existence of trapped components in eucrites which have ^N/^N ratios different from the atmospheric value. Since there may be some contribution of terrestrial or cosmogenic nitrogen even at medium temperature fractions, the minimum values observed in the present work should be considered as upper limits for the trapped components

Isotopic composition of nitrogen in the PCA 91002 R group chondrite

Nitrogen isotopic composition of an R-group chondrite PCA 91002 was measured. A delta ^N value as low as -60 permil was found in some combustion steps. Since this is a gas-rich meteorite, interpretation of the result is not straightforward, but with the aid of results on an H_2O_2-treated sample, we conclude that isotopically light nitrogen is indigenous to the meteorite

Magnetic Characteristics of Some Yamato Meteorites─Magnetic Classification of Stone Meteorites─

13 Yamato stone meteorites have been magnetically examined. They are one enstatite chondrite (E), 6 olivine-bronzite chondrites (H), 2 olivine-hypersthene chondrites (L), one carbonaceous chondrite (C) and 3 achondrites (aC). The intrinsic magnetic parameters of these stone meteorites obtained from their magnetic hysteresis curves and thermomagnetic curves, together with those of other 7 known chondritic meteorites, are specifically examined in terms of the compositional and petrographical classification of stone meteorites. The saturation magnetization (I_s) and major magnetic transition temperature (Θ_c) in the cooling process can be taken as the representative magnetic parameters in the proposed magnetic classification of stone meteorites. In the I_s versus Θ_c diagram, those examined stone meteorites, 25 in total, are separated into groups ; namely, I_s (E) > I_s (H) > I_s (L) > I_s (aC), Θ_c (H and L) < Θ_c (E and aC) &sime; 770℃, I_s (C) &sime; I_s (L) but Θ_c (C) < 600℃ < Θ_c (L). Although the boundary between the L-group and the H-group is not sharp enough in the I_s-Θ_c diagram, the L-group chondrites contain a distinctly larger amount of plessite phase which can be magnetically identified

Heavy nitrogen in the Yamato-74191 and the heterogeneity of the primitive solar nebula

A systematic search for presolar grains in ordinary chondrites was made by measuring isotopes of nitrogen. Only one chondrite (Yamato-74191) out of 20 ordinary chondrites showed the presence of very heavy nitrogen of probably presolar origin. The heavy nitrogen is not particularly concentrated in either magnetic nor non-magnetic fractions. The HF/HCl residue is enriched in nitrogen but the heavy nitrogen seems to have been lost by acid treatments. The carrier of the heavy nitrogen has not been identified. The release patterns of excess ^N are similar to those of primordial Ar. Chondrites more primitive than the Y-74191 do not contain the heavy nitrogen, suggesting heterogeneous distribution of the carrier of the heavy nitrogen. Together with evidence for the heterogeneous distribution of presolar SiC in meteorites, it is concluded that exotic materials were not well mixed in the primitive solar nebula

Sticking probabilities of fractal aggregates

An attempt was made to experimentally estimate the sticking probabilities of fractal aggregates of fine particles. The experiment was done using MgO fine particles floating in air under normal gravity. The growth in size of the aggregates was monitored by scattered He-Ne laser light. Our preliminary result suggests that the sticking probability decreases with increase in aggregate size. There are, however, still many uncertainties in the method of determining the sticking probabilities. Since this study is still at a developing stage, in this article we provide a general description of the experimental set-up, without giving details of various aspects of the problem

Magnetic Properties of Yamato-73-04 and Yamato-73-07 Meteorites

Two Yamato meteorites collected in 1973 in Antarcica, Yamato-73-04 and Yamato-73-07, may be identified to an olivine-bronzite chondrite and a hypersthene achondrite respectively from their petrographic and chemical compositions. Magnetic analyses indicate that native irons in Yamato-73-04 chondrite comprise 2.6wt% of 7wt% Ni kamacite and 4.3wt% of 13wt% Ni kamacite, and that Yamato-73-07 achondrite contains 0.24wt% of Fe^0 with small amounts of Ni and Co and less than 0.02wt% of 60wt% Ni taenite or Fe_Cr_xO_4. The natural remanent magnetization, NRM, of Yamato-73-07 achondrite can be distinctly separated into the original NRM of the undisturbed interior of 6.3×10^ emu/gm in intensity and the secondary NRM of the surface skin fusion crust of about 0.5mm in thickness. The secondary NRM is attributable to the thermoremanent magnetization acquired in a magnetic field of 0.44 Oe-probably the geomagnetic field

Nitrogen isotopic compositions of some solar-gas-rich chondrites

Isotopically heavy nitrogen was detected in three solar-gas-rich (Weston (H4), ALHA77278 (LL3.7) and Yamato-82133 (H3)) and one solar-gas-poor (LEW86018 (L3.1)) chondrites. Together with a previously studied solar-gas-rich chondrite, all solar-gas-rich chondrites that we examined have isotopically heavy nitrogen. Thus, we suggest that the solar nitrogen is isotopically heavy. The abundance of the heavy nitrogen is, however, not proportional to that of the solar Ne, suggesting complex processing on the surfaces of the parent bodies

Metallographic and Magentic Properties of a Yamato Iron Meteorite─Yamato-75-105

A Yamato iron meteroite, Yamato-75-105, examined chemically, metallographically and magnetically, has revealed that the major elements of the metal base of this iron meteorite are 5.65% Ni, 1.0% P, and 0.52% Co, in addition to Fe occupying the most parts. From the chemical composition and the microstructure, this iron meteorite can be classified as a reheated hexahedrite, i. e. a Ni-poor ataxite. An "ablation zone" about 2mm in thickness on the flat surface indicates an extensive reheating on entry into the earth\u27s atmosphere although traces of the original single-crystal features remain. Within the matrix of kamacite (95% Fe and 5% Ni) composition, Fe-Ni phosphide (schribersite ; 75% Fe, 10% Ni and 15% P) grains are enveloped by high-P kamacite of α-phase (91% Fe, 7% Ni and 2% P). These structures suggest that this meteorite specimen was reheated to above 1000℃. The acicular grain structure of the kamacite matrix indicates a rapid cooling rate after the reheating. Both metallographic and magnetic analyses have consistently revealed the above-mentioned conclusion

An attempt to reproduce petrographic features of mesosiderites

The Tenth Symposium on Polar Science/Poster presentations: [OA] Antarctic meteorites, Wed. 4 Dec. / Entrance Hall (1st floor), National Institute of Polar Researc