¹Takaaki Noguchi, ²Noriaki Ohashi, ²Shinichi Tsujimoto, ²Takuya Mitsunari, ³John P. Bradley, ⁴Tomoki Nakamura,
⁵Shoichi Toh, ⁶Thomas Stephan, ⁷Naoyoshi Iwata, ⁸Naoya Imae
¹Faculty of Arts and Science, Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan
²College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito 310-8512, Japan
³University of Hawaii at Manoa, Hawaii Institute of Geophysics and Planetology, Honolulu, HI 96822, USA
⁴Department of Earth Science, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan
⁵Department of Applied Physics, Fukuoka University, 8-19-1 Nanakuma, Fukuoka 814-0180, Japan
⁶Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
⁷Department of Earth and Environmental Sciences, Yamagata University, 1-4-12 Kojirakawa-machi, Yamagata 990-8560, Japan
⁸National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan

Chondritic porous interplanetary dust particles (CP IDPs) collected in the stratosphere are regarded as possibly being cometary dust, and are therefore the most primitive solar system material that is currently available for analysis in laboratories. In this paper we report the discovery of more than 40 chondritic porous micrometeorites (CP MMs) in the surface snow and blue ice of Antarctica, which are indistinguishable from CP IDPs. The CP MMs are botryoidal aggregates, composed mainly of sub-micrometer-sized constituents. They contain two components that characterize them as CP IDPs: enstatite whiskers and GEMS (glass with embedded metal and sulfides). Enstatite whiskers appear as <2-μm-long acicular objects that are attached on, or protrude from the surface, and when included in the interior of the CP MMs are composed of a unit-cell scale mixture of clino- and ortho-enstatite, and elongated along the [100] direction. GEMS appear as 100–500 nm spheroidal objects containing <50 nm Fe–Ni metal and Fe sulfide. The CP MMs also contain low-iron–manganese-enriched (LIME) and low-iron–chromium-enriched (LICE) ferromagnesian silicates, kosmochlor (NaCrSi2O6)-rich high-Ca pyroxene, roedderite (K, Na)2Mg5Si12O30, and carbonaceous nanoglobules. These components have previously been discovered in primitive solar system materials such as the CP IDPs, matrices of primitive chondrites, phyllosilicate-rich MMs, ultracarbonaceous MMs, and cometary particles recovered from the 81P/Wild 2 comet. The most outstanding feature of these CP MMs is the presence of kosmochlor-rich high-Ca pyroxene and roedderite, which suggest that they have building blocks in common with CP IDPs and cometary dust particles and therefore suggest a possible cometary origin of both CP MMs and CP IDPs. It is therefore considered that CP MMs are CP IDPs that have fallen to Earth and have survived the terrestrial environment.

Reference
Noguchia T, Ohashi N, Tsujimoto S, Mitsunari T, Bradley JP, Nakamura T, Toh S, Stephan T, Iwata N, Imae N (2014) Cometary dust in Antarctic ice and snow: Past and present chondritic porous micrometeorites preserved on the Earth’s surface. Earth and Planetary Science Letters 410,l 1-11
Link to Article [doi:10.1016/j.epsl.2014.11.012]

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