The mineralogy of cometary dust

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Abstract

Cometary dust is a heterogeneous mixture of unequilibrated olivine and pyroxenes, amorphous silicates, Fe-Ni sulfides, and minor amounts of oxides and other minerals. While forsterite Mg2SiO4 and enstatite MgSiO3 are the most common silicate minerals, both the olivine and pyroxenes also show a wide range in Mg/Fe in at least some comets. Carbon in the dust is enriched relative to CI chondrites; a significant fraction of the carbon is in the form of organic refractory material. The return of the particulate sample from ecliptic comet 81P/Wild 2 has opened up a new window for revealing the dust mineralogy at a level of detail not previously possible. The most interesting result from the Wild 2 sample to date is the discovery of refractory calcium aluminum-rich inclusions (CAI) similar to those found in primitive meteorites; chondrule fragments are also present. Comets formed in the outer parts of the solar nebula where temperatures remained low enough so that interstellar grains could have survived. The small glassy silicates in comets may indeed be interstellar grains. The CAI and the widespread, abundant crystalline silicates must have condensed in the hot inner solar nebula; their presence in comets is evidence for strong radial mixing in the solar nebula. The preponderance of Mg-rich silicates has a natural explanation in the condensation sequence; they are the first to condense in a hot gas and only react with iron at lower temperatures. This review discusses the mineralogy of cometary dust determined from infrared spectroscopy, in situ Halley measurements, IDPs, and the captured particles from comet Wild 2. © 2010 Springer Berlin Heidelberg.

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Hanner, M. S., & Zolensky, M. E. (2010). The mineralogy of cometary dust. Lecture Notes in Physics, 815, 203–232. https://doi.org/10.1007/978-3-642-13259-9_4

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