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Paper: The Early Micrometeorites Accretion Scenario and the Origin of Earth's
Volume: 213, Bioastronomy '99: A New Era in Bioastronomy
Page: 263
Authors: Maurette, Michel; Gounelle, M.; Duprat, J.; Engrand, C.; Matrajt, G.
Abstract: Unmelted large micrometeorites with sizes of about 50-500 microns were recovered from the Antarctica and Greenland ice sheets. Their capture in such ``space collectors'' made of very clean ices, where they got both shielded from most terrestrial contaminants and preserved by deep freeze, allowed for the first time the investigation of their carbon chemistry. Mass flux measurements in both ice sheets indicate that micrometeorites in this size range represent by far the dominant extraterrestrial material that survive upon impact with the Earth. Mineralogical, chemical and isotopic compositions show that they are mainly related to the relatively rare group of the CM-type hydrous-carbonaceous chondrites (< 2% of the meteorite falls) and not to the most abundant meteorites (1). But marked differences between these two classes of objects indicate that the parent bodies of micrometeorites represent a new population of solar system objects, strongly depleted in both differentiated objects and chondrules, and which probably originated in the outer solar system. This conclusion is further supported by a recent comparison between the silicate mineralogy of micrometeorites and that of the coma of the Hale-Bopp comet (2), both showing pyroxene to olivine ratios at least 10 times larger than those measured in carbonaceous chondrites (with the exception of the CR chondrites).
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